Mitochondria hold diverse and pivotal roles in fundamental processes that govern cell survival, differentiation, and death, in addition to organismal growth, maintenance, and aging. The mitochondrial protein import system is a major contributor to mitochondrial biogenesis and lies at the crossroads between mitochondrial and cellular homeostasis. Recent findings highlight the mitochondrial protein import system as a signaling hub, receiving inputs from other cellular compartments and adjusting its function accordingly. Impairment of protein import, in (...) a physiological, or disease context, elicits adaptive responses inside and outside mitochondria. In this review, we discuss recent developments, relevant to the mechanisms of mitochondrial protein import regulation, with a particular focus on quality control, proteostatic and metabolic cellular responses, triggered upon impairment of mitochondrial protein import. (shrink)

Mitochondrial function is key for maintaining cellular health, while mitochondrial failure is associated with various pathologies, including inherited metabolic disorders and age‐related diseases. In order to maintain mitochondrial quality, several pathways of mitochondrial quality control have evolved. These systems monitor mitochondrial integrity through antioxidants, DNA repair systems, and chaperones and proteases involved in the mitochondrial unfolded protein response. Additional regulation of mitochondrial function involves dynamic exchange of components through mitochondrial (...) fusion and fission. Sustained stress induces a selective autophagy – termed mitophagy – and ultimately leads to apoptosis. Together, these systems form a network that acts on the molecular, organellar, and cellular level. In this review, we highlight how these systems are regulated in an integrated context‐ and time‐dependent network of mitochondrial quality control that is implicated in healthy aging. (shrink)

The endoplasmic reticulum (ER) organelle is the key intracellular site of both protein and lipid biosynthesis. ER dysfunction, termed ER stress, can result in protein accretion within the ER and cell death; a pathophysiological process contributing to a range of metabolic diseases and cancers. ER stress leads to the activation of a protective signalling cascade termed the Unfolded Protein Response (UPR). However, chronic UPR activation can ultimately result in cellular apoptosis. Emerging evidence suggests that cells (...) undergoing ER stress and UPR activation can release extracellular signals that can propagate UPR activation to target tissues in a cell non‐autonomous signalling mechanism. Separately, studies have determined that the UPR plays a key regulatory role in the biosynthesis of bioactive signalling lipids including sphingolipids and ceramides. Here we weigh the evidence to combine these concepts and propose that during ER stress, UPR activation drives the biosynthesis of ceramide lipids, which are exported and function as cell non‐autonomous signals to propagate UPR activation in target cells and tissues. (shrink)

Recently, several studies have demonstrated that tetracyclines, the antibiotics most intensively used in livestock and that are also widely applied in biomedical research, interrupt mitochondrial proteostasis and physiology in animals ranging from round worms, fruit flies, and mice to human cell lines. Importantly, plant chloroplasts, like their mitochondria, are also under certain conditions vulnerable to these and other antibiotics that are leached into our environment. Together these endosymbiotic organelles are not only essential for cellular and organismal homeostasis stricto sensu, (...) but also have an important role to play in the sustainability of our ecosystem as they maintain the delicate balance between autotrophs and heterotrophs, which fix and utilize energy, respectively. Therefore, stricter policies on antibiotic usage are absolutely required as their use in research confounds experimental outcomes, and their uncontrolled applications in medicine and agriculture pose a significant threat to a balanced ecosystem and the well‐being of these endosymbionts that are essential to sustain health.Also watch theVideo Abstract. (shrink)

Post‐transcriptional tRNA modifications contribute to the decoding efficiency of tRNAs by supporting codon recognition and tRNA stability. Recent work shows that the molecular and cellular functions of tRNA modifications and tRNA‐modifying‐enzymes are linked to brain development and neurological disorders. Lack of these modifications affects codon recognition and decoding rate, promoting protein aggregation and translational stress response pathways with toxic consequences to the cell. In this review, we discuss the peculiarity of local translation in neurons, suggesting a role for (...) fine‐tuning of translation performed by tRNA modifications. We provide several examples of tRNA modifications involved in physiology and pathology of the nervous system, highlighting their effects on protein translation and discussing underlying mechanisms, like the unfolded protein response (UPR), ribosome quality control (RQC), and no‐go mRNA decay (NGD), which could affect neuronal functions. We aim to deepen the understanding of the roles of tRNA modifications and the coordination of these modifications with the protein translation machinery in the nervous system. (shrink)

Neither the pathogenesis nor the aetiology of Down's syndrome (DS) are clearly understood. Numerous studies have examined whether clinical features of DS are a consequence of specific chromosome 21 segments being triplicated. There is no evidence, however, that individual loci are responsible, or that the oxidative damage in DS could be solely explained by a gene dosage effect. Using astrocytes and neuronal cultures from DS fetuses, a recent paper shows that altered metabolism of the amyloid precursor protein and oxidative (...) stress result from mitochondrial dysfunction.1 These findings are consistent with considerable data implicating the role of the mitochondrial genome in DS pathogenesis and aetiology. BioEssays 24:681–684, 2002. © 2002 Wiley Periodicals, Inc. (shrink)

The ribosomal polypeptide tunnel exit is the site where a variety of factors interact with newly synthesized proteins to guide them through the early steps of their biogenesis. In mitochondrial ribosomes, this site has been considerably modified in the course of evolution. In contrast to all other translation systems, mitochondrial ribosomes are responsible for the synthesis of only a few hydrophobic membrane proteins that are essential subunits of the mitochondrial respiratory chain. Membrane insertion of these proteins occurs (...) co‐translationally and is connected to a sophisticated assembly process that not only includes the assembly of the different subunits but also the acquisition of redox co‐factors. Here, we describe how mitochondrial translation is organized in the context of respiratory chain assembly and speculate how alteration of the ribosomal tunnel exit might allow the establishment of a subset of specialized ribosomes that individually organize the early steps in the biogenesis of distinct mitochondrially‐encoded proteins. (shrink)

The biological membranes of eukaryotic cells harbor sensitive surveillance systems to establish, sense, and maintain characteristic physicochemical properties that ultimately define organelle identity. They are fundamentally important for membrane homeostasis and play active roles in cellular signaling, protein sorting, and the formation of vesicular carriers. Here, we compare the molecular mechanisms of Mga2 and Ire1, two sensors involved in the regulation of fatty acid desaturation and the response to unfolded proteins and lipid bilayer stress in order to (...) identify their commonalities and specializations. We will speculate on the cellular significance of membrane property sensors in other organelles and discuss their putative mechanisms. Based on these findings, we propose membrane property sensors as an emerging class of proteins with wide implications for organelle communication and function. (shrink)

Many innate immune response proteins recognize foreign nucleic acids from invading pathogens to initiate antiviral signaling. These proteins mostly rely on structural characteristics of the nucleic acids rather than their specific sequences to distinguish self and nonself. One feature utilized by RNA sensors is the extended stretch of double‐stranded RNA (dsRNA) base pairs. However, the criteria for recognizing nonself dsRNAs are rather lenient, and hairpin structure of self‐RNAs can also trigger an immune response. Consequently, aberrant activation of RNA (...) sensors has been reported in numerous human diseases. Yet, in most cases, the activating antigens remain unknown. Recent studies have developed sequencing techniques tailored to specifically capture dsRNAs and identified that various noncoding elements in the nuclear and the mitochondrial genome can generate dsRNAs. Here, the identity of endogenous dsRNAs, their recognition by dsRNA sensors, and their implications in the pathogenesis of human diseases ranging from inflammatory to degenerative are presented. (shrink)

Mitochondria are increasingly being recognized as information hubs that sense cellular changes and transmit messages to other cellular components, such as the nucleus, the endoplasmic reticulum (ER), the Golgi apparatus, and lysosomes. Nonetheless, the interaction between mitochondria and the nucleus is of special interest because they both host part of the cellular genome. Thus, the communication between genome‐bearing organelles would likely include gene expression regulation. Multiple nuclear‐encoded proteins have been known to regulate mitochondrial gene expression. On the contrary, no (...) mitochondrial‐encoded factors are known to actively regulate nuclear gene expression. MOTS‐c (mitochondrial open reading frame of the 12S ribosomal RNA type‐c) is a recently identified peptide encoded within the mitochondrial 12S ribosomal RNA gene that has metabolic functions. Notably, MOTS‐c can translocate to the nucleus upon metabolic stress (e.g., glucose restriction and oxidative stress) and directly regulate adaptive nuclear gene expression to promote cellular homeostasis. It is hypothesized that cellular fitness requires the coevolved mitonuclear genomes to coordinate adaptive responses using gene‐encoded factors that cross‐regulate the opposite genome. This suggests that cellular gene expression requires the bipartite split genomes to operate as a unified system, rather than the nucleus being the sole master regulator. (shrink)

Dietary methionine restriction (MR) is associated with a spectrum of health‐promoting benefits. Being conducive to prevention of chronic diseases and extension of life span, MR can activate integrated responses at metabolic, transcriptional, and physiological levels. However, how the mitochondria of MR influence metabolic phenotypes remains elusive. Here, we provide a summary of cellular functions of methionine metabolism and an overview of the current understanding of effector mechanisms of MR, with a focus on the aspect of mitochondria‐mediated responses. We propose that (...) mitochondria can sense and respond to MR through a modulatory role of lipoylation, a mitochondrial protein modification sensitized by MR. (shrink)

Progressive supranuclear palsy is a movement disorder with prominent tau neuropathology. Brain diseases with abnormal tau deposits are called tauopathies, the most common of which is Alzheimer's disease. Environmental causes of tauopathies include repetitive head trauma associated with some sports. To identify common genetic variation contributing to risk for tauopathies, we carried out a genome-wide association study of 1,114 individuals with PSP and 3,247 controls followed by a second stage in which we genotyped 1,051 cases and 3,560 controls for the (...) stage 1 SNPs that yielded P ≤ 10-3. We found significant previously unidentified signals associated with PSP risk at STX6, EIF2AK3 and MOBP. We confirmed two independent variants in MAPT affecting risk for PSP, one of which influences MAPT brain expression. The genes implicated encode proteins for vesicle-membrane fusion at the Golgi-endosomal interface, for the endoplasmic reticulum unfolded protein response and for a myelin structural component. © 2011 Nature America, Inc. All rights reserved. (shrink)

Uncoupling proteins (UCPs) regulate mitochondrial function, and thus cellular metabolism. Angiotensin‐converting enzyme (ACE) is the central component of endocrine and local tissue renin–angiotensin systems (RAS), which also regulate diverse aspects of whole‐body metabolism and mitochondrial function (partly through altering mitochondrial UCP expression). We show that ACE expression also appears to be regulated by mitochondrial UCPs. In genetic analysis of two unrelated populations (healthy young UK men and Scandinavian diabetic patients) serum ACE (sACE) activity was significantly higher (...) amongst UCP3‐55C (rather than T) and UCP2 I (rather than D) allele carriers. RNA interference against UCP2 in human umbilical vein endothelial cells reduced UCP2 mRNA sixfold (P < 0·01) whilst increasing ACE expression within a physiological range (<1·8‐fold at 48 h; P < 0·01). Our findings suggest novel hypotheses. Firstly, cellular feedback regulation may occur between UCPs and ACE. Secondly, cellular UCP regulation of sACE suggests a novel means of crosstalk between (and mutual regulation of) cellular and endocrine metabolism. This might partly explain the reduced risk of developing diabetes and metabolic syndrome with RAS antagonists and offer insight into the origins of cardiovascular disease in which UCPs and ACE both play a role. (shrink)

Adipose tissue plays an important role in mammalian energy equilibrium not only as a lipid‐dissipating, i.e. energy‐storing, tissue (white adipose tissue), but also as an energy‐dissipating one (brown adipose tissue). Brown adipocytes have the ability of facultative heat production due to a unique mitochondrial protein, the uncoupling protein (UCP). Differentiation of white and (to a lesser extent) brown adipocytes has been studied in different cell culture systems, which has led to the identification of external inducers, second messenger (...) pathways and transcription factors involved in adipocyte differentiation. Functional differentiation of white adipocytes implies adipose conversion, whereas in brown adipocytes it insinuates additionally the development of a thermogenic function. This review discusses recent advances in the elucidation of the pathways responsible for, and the molecular bases of, adipose conversion on the one hand and development of the thermogenic properties of brown adipocytes on the other. (shrink)

The discovery of the concrete basis for genes, and especially the clarification of mechanisms regulating gene expressions (in particular those that bear on the stepwise processing of hereditary information from the sequences of DNA nucleotides to the proteins) was to give flesh to the concept of a genetic program, for these regulations introduce relationships of order between the various elements of information contained in the genes. These order relations are then revealed during the time-dependent expression of the genetic program. They (...) can lead, in the case of a given program, to a plethora of particular outcomes, because the number of possible combinations rapidly becomes enormous. Since the discoveries of Jacob and Monod, it is clear that the genes specifying the regulatory functions will be responsible for phenotypic variability, especially for the apparently ideal adaptation of a living organism to its environment, and more generally for all the genotype-bound manifestations as they unfold in time. -/- Thus we are led to consider three particular characteristics that allow for the representation of living beings: a program, which summarizes the hereditary constraints and is, in fact, the abstract notion underlying the definition of all individuals in a given class (species); an initial state of the system that represents the context in which the program must express itself at the time of the individual's birth; and a particular outcome of each program, which coincides with individual development. The set of all outcomes constitutes the genetic envelope and allows the essential characteristics of the program to be obtained by induction. Theoretically, a structured set equivalent to the aforementioned one could be reconstructed by providing the program, the initial state, and the totality of the events of the external environment, producing any interaction whatever with the individual. -/- As a consequence, the observation of a phenotype does not tell in any straightforward way, what is the direct consequence of the expression of a particular gene, or of a specific feature of the environment. A phenocopy is a particular example of a phenotype that is the result of a gene expression mimicking a particular gene-directed phenotype, without however corresponding to a pparticular mutation of a known gene. (shrink)

Since their discovery over two decades ago, the molecular and cellular functions of the NIPSNAP family of proteins (NIPSNAPs) have remained elusive until recently. NIPSNAPs interact with a variety of mitochondrial and cytoplasmic proteins. They have been implicated in multiple cellular processes and associated with different physiologic and pathologic conditions, including pain transmission, Parkinson's disease, and cancer. Recent evidence demonstrated a direct role for NIPSNAP1 and NIPSNAP2 proteins in regulation of mitophagy, a process that is critical for cellular health (...) and maintenance. Importantly, NIPSNAPs contain a 110 amino acid domain that is evolutionary conserved from mammals to bacteria. However, the molecular function of the conserved NIPSNAP domain and its potential role in mitophagy have not been explored. It stands to reason that the highly conserved NIPSNAP domain interacts with a substrate that is ubiquitously present across all species and can perhaps act as a sensor for mitochondrial health. (shrink)

The pore‐forming BCL‐2 family proteins are effectors of mitochondrial poration in apoptosis initiation. Two atypical effectors—BOK and truncated BID (tBID)—join the canonical effectors BAK and BAX. Gene knockout revealed developmental phenotypes in the absence the effectors, supporting their roles in vivo. During apoptosis effectors are activated and change shape from dormant monomers to dynamic oligomers that associate with and permeabilize mitochondria. BID is activated by proteolysis, BOK accumulates on inhibition of its degradation by the E3 ligase gp78, while BAK (...) and BAX undergo direct activation by BH3‐only initiators, autoactivation, and crossactivation. Except tBID, effector oligomers on the mitochondria appear as arcs and rings in super‐resolution microscopy images. The BH3‐in‐groove dimers of BAK and BAX, the tBID monomers, and uncharacterized BOK species are the putative building blocks of apoptotic pores. Effectors interact with lipids and bilayers but the mechanism of membrane poration remains elusive. I discuss effector‐mediated mitochondrial poration. (shrink)

Protein translocation across biological membranes is of fundamental importance for the biogenesis of organelles and in protein secretion. We will give an overview of the recent achievements in the understanding of protein translocation across mitochondrial membranes(1‐5). In particular we will focus on recently identified components of the mitochondrial import apparatus.

Germ cells are cross-roads of development and evolution. They define the origin of every new generation and, at the same time, represent the biological end-product of any mature organism. Germ cells are endowed with the following capacities: to store a self-descriptive program, to accumulate a protein-synthesizing machinery, and to incorporate enough nourishment to sustain embryonic development. To accomplish this goal, germ cells do not simply unfold a pre-determined program or realize a sole instructive role. On the contrary, due to (...) the complexity of their cytoarchitecture and the nature of the soma-to-germ interactions, they are heavily involved in processes of sign recognition and meaningful tissue exploration. At each stage of their inward migration, germ plasma membranes act as semiotic interfaces allowing cells to interact with the surrounding extracellular milieu and experience the compatibility of selected developmental sequences. The question of which signaling pathways are activated at each developmental stage does not result from a strictly predetermined program instructing germ cell stemness. Rather, each developmental sequence is an open-ended semiotic relationship explored and gradually defined during evolution by the context-dependency of specific cell-to-cell interactions. In this way, any structural and functional novelty that has emerged in the course of germ cell interactions may be interpreted as an exaptation fixed in the species genome in response to specific environmental constraints. (shrink)

Affective disorders arise in stressful situations from aberrant sensory information integration that affects energetic nutrient (i.e., glucose) utilization to the cognitive centers of the brain. Because energy flow is mediated by molecular signals and receptors that evolved before the first complex brains, the phylogenetically oldest signaling systems are essential in the etiology of affective disorders. The corticotropin‐releasing factor (CRF) peptide subfamily is a phylogenetically old metazoan peptide family and is pivotal for regulating organismal energy response associated with stress. Highly (...) conserved, both the CRF peptide family and its receptors possess a structural relationship to the teneurins, and their receptors, latrophilins, respectively. The CRF homologous region of teneurin is defined as the “teneurin C‐terminal associated peptide” (TCAP) and antagonizes CRF action, regulates mitochondrial energy production, and is anxiolytic in vivo. Here, it is postulated that TCAP represents an ancient peptide that mediates intercellular information transfer of stressful and noxious events by regulating energy utilization among neurons. (shrink)

E4BP4, a mammalian basic leucine zipper (bZIP) transcription factor, was first identified through its ability to bind and repress viral promoter sequences. Subsequently, E4BP4 and homologues in other species have been implicated in a diverse range of processes including commitment to cell survival versus apoptosis, the anti‐inflammatory response and, most recently, in the mammalian circadian oscillatory mechanism. In some of these cases at least, E4BP4 appears to act antagonistically with members of the related PAR family of transcription factors with (...) which it shares DNA‐binding specificity. This diversity of function is mirrored by the regulatory pathways impinging on E4BP4, which include regulation by ras via the lymphokine IL‐3 in murine B‐cells, by thyroid hormone during Xenopus tail resorption, by glucocorticoids in murine fibroblasts and by calcium in rat smooth muscle cells. This article will cover the unfolding role/s of and regulation of E4BP4, E4BP4‐like proteins and PAR factors in species as diverse as mouse and C. elegans. BioEssays 24:1023–1029, 2002. © 2002 Wiley‐Periodicals, Inc. (shrink)

At extreme altitude (>5,000 – 5,500 m), sustained hypoxia threatens human function and survival, and is associated with marked involuntary weight loss (cachexia). This seems to be a coordinated response: appetite and protein synthesis are suppressed, and muscle catabolism promoted. We hypothesise that, rather than simply being pathophysiological dysregulation, this cachexia is protective. Ketone bodies, synthesised during relative starvation, protect tissues such as the brain from reduced oxygen availability by mechanisms including the reduced generation of reactive oxygen species, (...) improved mitochondrial efficiency and activation of the ATP‐sensitive potassium (KATP) channel. Amino acids released from skeletal muscle also protect cells from hypoxia, and may interact synergistically with ketones to offer added protection. We thus propose that weight loss in hypoxia is an adaptive response: the amino acids and ketone bodies made available act not only as metabolic substrates, but as metabolic modulators, protecting cells from the hypoxic challenge.Also watch the Video Abstract. (shrink)

Ribosome biogenesis includes the making and processing of ribosomal RNAs, the biosynthesis of ribosomal proteins from their mRNAs in the cytosol and their transport to the nucleolus to assemble pre‐ribosomal particles. Several stresses including cellular senescence reduce nucleolar rRNA synthesis and maturation increasing the availability of ribosome‐free ribosomal proteins. Several ribosomal proteins can activate the p53 tumor suppressor pathway but cells without p53 can still arrest their proliferation in response to an imbalance between ribosomal proteins and mature rRNA production. (...) Recent results on senescence‐associated ribogenesis defects (SARD) show that the ribosomal protein S14 (RPS14 or uS11) can act as a CDK4/6 inhibitor linking ribosome biogenesis defects to the main engine of cell cycle progression. This work offers new insights into the regulation of the cell cycle and suggests novel avenues to design anticancer drugs. (shrink)

Auxin is a key regulator of plant developmental processes. Its effects on transcription are mediated by the AUXIN RESPONSE FACTOR (ARF) family of transcription factors. ARFs tightly control specific auxin responses necessary for proper plant growth and development. Recent research has revealed that regulated ARF protein accumulation and ARF nucleo‐cytoplasmic partitioning can determine auxin transcriptional outputs. In this review, we explore these recent findings and consider the potential for regulated ARF accumulation in driving auxin responses in plants.

Mitochondrial replacement techniques are intended to avoid the transmission of mitochondrial diseases from mother to child. MRT represent a potentially powerful new biomedical technology with ethical, policy, economic and social implications. Among other ethical questions raised are concerns about the possible effects on the identity of children born from MRT, their families, and the providers or donors of mitochondria. It has been suggested that MRT can influence identity directly, through altering the genetic makeup and physical characteristics of the (...) child, or indirectly through changing the child's experience of disease, and by generating novel intrafamilial relationships that shape the sense of self. In this article I consider the plausibility and ethical implications of these proposed identity effects, but I focus instead on a third way in which identity may be affected, through the mediating influence of the wider social world on MRT effects on identity. By taking a narrative approach, and examining the nature and availability of identity narratives, I conclude that while neither direct genetic nor indirect experiential effects can be excluded, social responses to MRT are more likely to have a significant and potentially damaging influence on the generation of MRT children's narratives of identity. This conclusion carries some implications for the collective moral responsibility we hold to ensure that MRT, if implemented, are practised in ethically justifiable ways. (shrink)

Mitochondrial function and biogenesis depend on the transport of a large variety of proteins, ions, and metabolites across the two surrounding membranes. While several specific transporters are present in the inner membrane, transport processes across the outer membrane are less understood. Recent studies reveal that the number of outer membrane channels and their transport mechanisms are more diverse than originally thought. Four protein‐conducting channels promote transport of distinct sets of precursor proteins across and into the outer membrane. The (...) voltage‐dependent anion channel (VDAC) forms the major channel for small hydrophilic molecules. In addition, three channels with yet unknown substrate specificity exist in the outer membrane. In this review, we outline the emerging functional diversity, selectivity, and regulation of mitochondrial outer membrane channels. The presence of several channel‐forming proteins challenges the traditional view that the outer membrane forms an unspecific size‐exclusion filter for the flux of small hydrophilic molecules. (shrink)

Technical, ethical, and social questions of germ-line gene interventions have been widely discussed in the literature. The majority of these discussions focus on planned interventions executed on the nuclear DNA (nDNA). However, human cells also contain another set of genes that is the mitochondrial DNA (mtDNA). As the characteristics of the mtDNA grossly differ from those of nDNA, so do the social, ethical, psychological, and safety considerations of possible interventions on this part of the genetic substance.

Children created through mitochondrial replacement techniques (MRTs) are commonly presented as possessing 50% of their mother’s nuclear DNA, 50% of their father’s nuclear DNA and the mitochondrial DNA of an egg donor. This lab-engineered genetic composition has prompted two questions: Do children who are the product of an MRT procedure have threegeneticparents? And, do MRT egg donors have parental responsibilities for the children created? In this paper, I address the second question and in doing so I also address (...) the first one. First, I present a brief account of mitochondrial diseases and MRTs. Second, I examine how MRTs affect the numerical identity of eggs and zygotes. Third, I investigate two genetic accounts of parenthood and MRT egg donation. Fourth, I explore three causal accounts of parenthood and MRT egg donation. My conclusion is that, under the appropriate circumstances, MRT egg donors are parentally responsible for the children created under genetic accounts of parenthood and under causal accounts of parenthood. (shrink)

Germ-line therapy has long been regarded with great caution both by scientists and by ethicists. Even those who do not reject germ-line therapy in principle have tended to reject it in practice as carrying unacceptable risks in our current state of knowledge. For this reason, a recent paper by Rubenstein, Thomasma, Shon, and Zinaman is unusual in putting forward a serious proposal for the use of germ-line therapy in the foreseeable future.

Mitochondrial replacement therapy (MRT), also called nuclear genome transfer and mitochondrial donation, is a new technique that can be used to prevent the transmission of mitochondrial DNA diseases. Apart from the United Kingdom, the first country to approve MRT in 2015, Australia became the second country with a clear regulatory path for the clinical applications of this technique in 2021. The rapidly evolving clinical landscape of MRT makes the elaboration and evaluation of the responsible use of this (...) technology a pressing matter. As jurisdictions with less strict or non-existent reproductive laws are continuing to use MRT in the clinical context, the need to address the underlying ethical issues surrounding MRT’s clinical translation is fundamental. (shrink)

Multisubunit protein complexes are essential for cellular function. Genetic analysis of essential processes requires special tools, among which temperature‐sensitive (Ts) mutants have historically been crucial. Many researchers assume that the effect of temperature on such mutants is to drive their proteolytic destruction. In fact, degradation‐mediated elimination of mutant proteins likely explains only a fraction of the phenotypes associated with Ts mutants. Here I discuss insights gained from analysis of Ts mutants in oligomeric proteins, with particular focus on the study (...) of septins, GTP‐binding subunits of cytoskeletal filaments whose structures and functions are the subject of current investigation in my and many other labs. I argue that the kinds of unbiased forward genetic approaches that generate Ts mutants provide information that is largely inaccessible to modern reverse genetic methodologies, and will continue to drive our understanding of higher‐order assembly by septins and other oligomeric proteins.Also watch the Video Abstract. (shrink)

Much research has focused on the effects of pathogenic mitochondrial mutations on health. Notwithstanding, the mechanisms regulating the link between these mutations and their effects remain elusive in several cases. Here, we propose that certain mitochondrial mutations may disrupt function of a set of mitochondrial‐transcribed small RNAs, perturbing communication between mitochondria and nucleus, leading to disease. Our hypothesis synthesises two lines of supporting evidence. First, several mitochondrial mutations cannot be directly linked to effects on energy production (...) or protein synthesis. Second, emerging studies have described the existence of small RNAs encoded by the mitochondria and proposed their involvement in RNA interference. We present a roadmap to testing this hypothesis. (shrink)

A recent paper by Nisoli et al.1 provides the first evidence that elevated levels of nitric oxide (NO) stimulate mitochondrial biogenesis in a number of cell lines via a soluble guanylate‐cyclase‐dependent signaling pathway that activates PGC1α (peroxisome proliferator‐activated receptor γ coactivator‐1α), a master regulator of mitochondrial content. These results raise intriguing possibilities for a role of NO in modulating mitochondrial content in response to physiological stimuli such as exercise or cold exposure. However, whether this signaling cascade (...) represents a widespread mechanism by which mammalian tissues regulate mitochondrial content, and how it might integrate with other pathways that control PGC1α expression, remain unclear. BioEssays 25:538–541, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Fold‐switching proteins, which remodel their secondary and tertiary structures in response to cellular stimuli, suggest a new view of protein fold space. For decades, experimental evidence has indicated that protein fold space is discrete: dissimilar folds are encoded by dissimilar amino acid sequences. Challenging this assumption, fold‐switching proteins interconnect discrete groups of dissimilar protein folds, making protein fold space fluid. Three recent observations support the concept of fluid fold space: (1) some amino acid sequences interconvert (...) between folds with distinct secondary structures, (2) some naturally occurring sequences have switched folds by stepwise mutation, and (3) fold switching is evolutionarily selected and likely confers advantage. These observations indicate that minor amino acid sequence modifications can transform protein structure and function. Consequently, proteomic structural and functional diversity may be expanded by alternative splicing, small nucleotide polymorphisms, post‐translational modifications, and modified translation rates. (shrink)

Mitochondrial genomes represent relict bacterial genomes derived from a progenitor α‐proteobacterium that gave rise to all mitochondria through an ancient endosymbiosis. Evolution has massively reduced these genomes, yet despite relative simplicity their organization and expression has developed considerable novelty throughout eukaryotic evolution. Few organisms have reengineered their mitochondrial genomes as thoroughly as the protist lineage of dinoflagellates. Recent work reveals dinoflagellate mitochondrial genomes as likely the most gene‐impoverished of any free‐living eukaryote, encoding only two to three proteins. (...) The organization and expression of these genomes, however, is far from the simplicity their gene content would suggest. Gene duplication, fragmentation, and scrambling have resulted in an inflated and complex genome organization. Extensive RNA editing then recodes gene transcripts, and trans‐splicing is required to assemble full‐length transcripts for at least one fragmented gene. Even after these processes, messenger RNAs (mRNAs) lack canonical start codons and most transcripts have abandoned stop codons altogether. (shrink)

The process of protein folding in the cell is now known to depend on the action of other proteins. These proteins include molecular chaperones, Which interact non‐covalently with proteins as they fold and improve the final yields of active protein in the cell. The precise mechanism by which molecular chaperones act is obscure. Experiments reported recently(1) show that for one molecular chaperone (Cpn60, typified by the E. coli protein GroEL), the folding reaction is driven by cycles of (...) binding and release of the co‐chaperone Cpn10 (known as GroES in E. coli). These alternate with binding and release of the unfolded protein substrate. These cycles come about because of the opposite effects of Cpn10 and unfolded protein on the Cpn60 complex: the former stabilises the ADP‐bound state of Cpn60, whereas the latter stimulates ADP‐ATP exchange. This model proposes that the substrate protein goes through multiple cycles of binding and release, and is released into the cavity of the Cpn60 complex where it can undergo folding without interacting with other nearby folding intermediates. This is consistent with the ability of Cpn60 proteins to enhance folding by blocking pathways to aggregation. (shrink)

Regulators of G protein signaling (RGS) proteins provide timely termination of G protein‐coupled receptor (GPCR) responses. Serving as a central control point in GPCR signaling cascades, RGS proteins are promising targets for drug development. In this review, we discuss the involvement of RGS proteins in the pathophysiology of the gastrointestinal inflammation and their potential to become a target for anti‐inflammatory drugs. Specifically, we evaluate the emerging evidence for modulation of selected receptor families: opioid, cannabinoid and serotonin by RGS (...) proteins. We discuss how the regulation of RGS protein level and activity may modulate immunological pathways involved in the development of intestinal inflammation. Finally, we propose that RGS proteins may serve as a prognostic factor for survival rate in colorectal cancer. The ideas introduced in this review set a novel conceptual framework for the utilization of RGS proteins in the treatment of gastrointestinal inflammation, a growing major concern worldwide. (shrink)

MPZL3 is a nuclear‐encoded, mitochondrially localized, immunoglobulin‐like V‐type protein that functions as a key regulator of epithelial cell differentiation, lipid metabolism, ROS production, glycemic control, and energy expenditure. Recently, MPZL3 has surfaced as an important modulator of sebaceous gland function and of hair follicle cycling, an organ transformation process that is also governed by peripheral clock gene activity and PPARγ. Given the phenotype similarities and differences between Mpzl3 and Pparγ knockout mice, we propose that MPZL3 serves as a signaling (...) hub that is regulated by core clock gene products and/or PPARγ to translate signals from these nuclear transcription factors to the mitochondria to modulate circadian and metabolic regulation. Conservation between murine and human MPZL3 suggests that human MPZL3 may have similarly complex functions in health and disease. We summarize current knowledge and discuss future directions to elucidate the full spectrum of MPZL3 functions in mammalian physiology. (shrink)

Recent findings necessitate revision of the traditional view of G protein‐coupled receptor (GPCR) signaling and expand the diversity of mechanisms by which receptor signaling influences cell behavior in general. GPCRs elicit signals at the plasma membrane and are then rapidly removed from the cell surface by endocytosis. Internalization of GPCRs has long been thought to serve as a mechanism to terminate the production of second messengers such as cAMP. However, recent studies show that internalized GPCRs can continue to either (...) stimulate or inhibit cAMP production in a sustained manner. They do so by remaining associated with their cognate G protein subunit and adenylyl cyclase at endosomal compartments. Once internalized, the GPCRs produce cellular responses distinct from those elicited at the cell surface. (shrink)

The SARS‐CoV‐2 virus is responsible for the COVID‐19 pandemic the world experience since 2019. The protein responsible for the first steps of cell invasion, the spike protein, has probably received the most attention in light of its central role during infection. Computational approaches are among the tools employed by the scientific community in the enormous effort to study this new affliction. One of these methods, namely molecular dynamics (MD), has been used to characterize the function of the spike (...) protein at the atomic level and unveil its structural features from a dynamic perspective. In this review, we focus on these main findings, including spike protein flexibility, rare S protein conformational changes, cryptic epitopes, the role of glycans, drug repurposing, and the effect of spike protein variants. (shrink)

Mitochondria contain a molecular genetic system to express the 13 protein components of the electron transport system encoded in the mitochondrial genome (mtDNA). Defects in the function of this system result in some diaseases, many of which are multisystem disorders, prominently involving highly aerobic, postmitotic tissues. These defects can be caused by large‐scale rearrangements of mtDNA, by point mutations, or by nuclear gene mutations resulting in abnormalities in mtDNA. Although any of these mutations would be expected to produce (...) a similar clinical phenotype by compromising oxidative phosphorylation, the surprising and puzzling result is that different clinical phenotypes are generally associated with specific mtDNA mutations. Moreover, the same mutation can produce a distinct clinical phenotype in different individuals or pedigrees. MtDNA rearrangements are also found in aged individuals, but at a subclinical level, suggesting that normal and pathological processes can differ by the effect of genetic or environmental factors on the error rate of mtDNA replication. (shrink)

In the bacterium Escherichia coli, the AraC protein positively and negatively regulates expression of the proteins required for the uptake and catabolism of the sugar L‐arabinose. This essay describes how work from my laboratory on this system spanning more than thirty years has aided our understanding of positive regulation, revealed DNA looping (a mechanism that explains many action‐at‐a‐distance phenomena) and, more recently, has uncovered the mechanism by which arabinose shifts AraC from a state where it prefers to bind to (...) two well‐separated DNA half‐sites and form a DNA loop to a state where it binds to two adjacent half‐sites and activates transcription. This work required learning how to assay, purify, and work with a protein possessing highly uncooperative biochemical properties. Present work is focussed on understanding arabinose‐responsive mechanism in atomic detail and is also directed towards understanding protein structure and function well enough to be able to engineer the allosteric mechanism seen in AraC onto other proteins. BioEssays 25:274–282, 2003. © 2003 Wiley Periodicals, Inc. (shrink)

Hypoxia hampers ATP production and threatens cell survival. Since cellular energetics tightly controls cell responses and fate, ATP levels and dynamics are of utmost importance. An integrated mathematical model of ATP synthesis by the mitochondrial oxidative phosphorylation/electron transfer chain system has been recently published :e36, 2005). This model was validated under static conditions. To evaluate its performance under dynamical situations, we implemented and simulated it . Inner membrane potential and [NADH] were used as indicators of mitochondrial function. Root (...) mean squared error was used to compare simulations and experiments :39155–39165, 2003). Steady-state experimental data were reproduced within 2–6%. Model dynamics were evaluated under: baseline, activation of NADH production, addition of ADP, addition of inorganic phosphate, oxygen exhaustion. In all phases, except the last one, ΔΨ and [NADH] as well as oxygen consumption, were reproduced . Under anoxia, simulated ΔΨ markedly depolarized . In conclusion, the model reproduces dynamic data as long as oxygen is present. Anticipated improvement by the inclusion of ATP consumption and explicit Krebs cycle are under evaluation. (shrink)

The mitochondrion is known as the “powerhouse” of eukaryotic cells since it is the main site of adenosine 5′‐triphosphate (ATP) production. Using a temperature‐sensitive fluorescent probe, it has recently been suggested that the stray free energy, not captured into ATP, is potentially sufficient to sustain mitochondrial temperatures higher than the cellular environment, possibly reaching up to 50 °C. By 50 °C, some DNA and mitochondrial proteins may reach their melting temperatures; how then do these biomolecules maintain their structure (...) and function? Further, the production of reactive oxygen species (ROS) accelerates with temperature, implying higher oxidative stresses in the mitochondrion than generally appreciated. Herein, it is proposed that mitochondrial heat shock proteins (particularly Hsp70), in addition to their roles in protein transport and folding, protect mitochondrial proteins and DNA from thermal and ROS damage. Other thermoprotectant mechanisms are also discussed. (shrink)

The tricarboxylic acid (TCA) or Krebs cycle, which takes place in prokaryotic cells and in the mitochondria of eukaryotic cells, is central to life on Earth and participates in key events such as energy production and anabolic processes. Despite its relevance, it is not perceived as tightly regulated compared to other key metabolisms such as glycolysis/gluconeogenesis. A better understanding of the functioning of the TCA cycle is crucial due to mitochondrial function impairment in several diseases, especially those that occur (...) with neurodegeneration. This article revisits what is known about the regulation of the Krebs cycle and hypothesizes the need for large‐scale, rapid regulation of TCA cycle enzyme activity. Evidence of mitochondrial enzyme activity regulation by activation/deactivation of protein kinases and phosphatases exists in the literature. Apart from indirect regulation via G protein‐coupled receptors (GPCRs) at the cell surface, signaling upon activation of GPCRs in mitochondrial membranes may lead to a direct regulation of the enzymes of the Krebs cycle. Hormonal‐like regulation by posttranscriptional events mediated by activable kinases and phosphatases deserve proper assessment using isolated mitochondria. Also see the video abstract here: https://youtu.be/aBpDSWiMQyI. (shrink)

Mitochondrial homeostasis serves as a cornerstone of cellular function, orchestrating a delicate balance between energy production, redox status, and cellular signaling transduction. This equilibrium involves a myriad of interconnected processes, including mitochondrial dynamics, quality control mechanisms, and biogenesis and degradation. Perturbations in mitochondrial homeostasis have been implicated in a wide range of diseases, including neurodegenerative diseases, metabolic syndromes, and aging‐related disorders. In the past decades, the discovery of numerous mitochondrial proteins and signaling has led to a (...) more complete understanding of the intricate mechanisms underlying mitochondrial homeostasis. Recent studies have revealed that Family with sequence similarity 210 member A (FAM210A) is a novel nuclear‐encoded mitochondrial protein involved in multiple aspects of mitochondrial homeostasis, including mitochondrial quality control, dynamics, cristae remodeling, metabolism, and proteostasis. Here, we review the function and physiological role of FAM210A in cellular and organismal health. This review discusses how FAM210A acts as a regulator on mitochondrial inner membrane to coordinate mitochondrial dynamics and metabolism. (shrink)

Responses to surprising events are dynamic. We argue that initial responses are primarily driven by the unexpectedness of the surprising event and reflect an interrupted and surprised state in which the outcome does not make sense yet. Later responses, after sense-making, are more likely to incorporate the valence of the outcome itself. To identify initial and later responses to surprising stimuli, we conducted two repetition-change studies and coded the general valence of facial expressions using computerised facial coding and specific facial (...) action using the Facial Action Coding System (FACS). Results partly supported our unfolding logic. The computerised coding showed that initial expressions to positive surprises were less positive than later expressions. Moreover, expressions to positive and negative surprises were initially similar, but after some time differentiated depending on the valence of the event. Importantly, these patterns were particularly pronounced in a subset of facially expressive participants, who also showed facial action in the FACS coding. The FACS data showed that the initial phase was characterised by limited facial action, whereas the later increase in positivity seems to be explained by smiling. Conceptual as well as methodological implications are discussed. (shrink)

While Dicer plays an important antiviral role through the RNAi pathway in plants and invertebrates, its contribution to antiviral immunity in vertebrates and more specifically mammals is more controversial. The apparent limited RNAi activity in mammalian cells has been attributed to the reduced long dsRNA processive activity of mammalian Dicer, as well as a functional incompatibility between the RNAi and IFN pathways. Why Dicer has lost this antiviral activity in the profit of the IFN pathway is still unclear. We propose (...) that the primary direct antiviral activity of Dicer has been functionally replaced by other sensors in the IFN pathway, leading to its specialization toward microRNA maturation. As a result, Dicer can regulate the innate immune response and prevent basal activation of the IFN pathway in mammals. Here, we discuss this hypothesis, highlighting how the adaptation of the helicase domain of mammalian Dicer may be key to this process. (shrink)

The Hippo pathway, a cascade of protein kinases that inhibits the oncogenic transcriptional coactivators YAP and TAZ, was discovered in Drosophila as a major determinant of organ size in development. Known modes of regulation involve surface proteins that mediate cell‐cell contact or determine epithelial cell polarity which, in a tissue‐specific manner, use intracellular complexes containing FERM domain and actin‐binding proteins to modulate the kinase activities or directly sequester YAP. Unexpectedly, recent work demonstrates that GPCRs, especially those signaling through Galpha12/13 (...) such as the protease activated receptor PAR1, cause potent YAP dephosphorylation and activation. This response requires active RhoA GTPase and increased assembly of filamentous (F‐)actin. Morever, cell architectures that promote F‐actin assembly per se also activate YAP by kinase‐dependent and independent mechanisms. These findings unveil the ability of GPCRs to activate the YAP oncogene through a newly recognized signaling function of the actin cytoskeleton, likely to be especially important for normal and cancerous stem cells. (shrink)