Mitochondria-cytoskeleton associations in mammalian cytokinesis

The genetics of preimplantation embryonic arrest: the role of aneuploidies

PURPOSE OF THE REVIEW

Aneuploidy is a major cause of embryonic arrest. While meiotic aneuploidies, especially maternal, are a well-documented cause of embryo and fetal arrest, increasing evidence highlights the crucial role played by mitotic aneuploidies. This review explores the molecular and cellular pathways underlying these abnormalities, focusing on abnormal cleavage, chromatin cohesion, spindle stability, maternal effect genes, and mitochondria.

RECENT FINDINGS

Approximately half of human embryos cease development in vitro or shortly after transfer to the uterus. Genetic investigation of these embryos has highlighted that 90% of these exhibit aneuploidies. Surprisingly, most of these arise from errors during the early mitotic divisions of preimplantation embryos. These findings strongly correlate with disruptions of early cleavage possibly due to faulty spindle assembly or mitochondrial dysfunction during the in-vitro development. Moreover, maternal effects, such as faulty meiotic recombination and variants in maternal effect genes involved in the subcortical maternal complex, may further predispose the embryo to high rates of chromosomal imbalance.

SUMMARY

Meiotic and mitotic aneuploidies play a significant role in embryo arrest, yet their molecular and cellular origin are not well understood. Investigating these pathways may lead to interventions that could be developed to improve success rates with IVF or even fertility rates in general.

Galectin-8 drives ERK-dependent mitochondrial fragmentation, perinuclear relocation and mitophagy, with metabolic adaptations for cell proliferation

Mitochondria adapt to the cell proliferative demands induced by growth factors through dynamic changes in morphology, distribution, and metabolic activity. Galectin-8 (Gal-8), a carbohydrate-binding protein that promotes cell proliferation by transactivating the EGFR-ERK signaling pathway, is overexpressed in several cancers. However, its impact on mitochondrial dynamics during cell proliferation remains unknown. Using MDCK and RPTEC kidney epithelial cells, we demonstrate that Gal-8 induces mitochondrial fragmentation and perinuclear redistribution. Additionally, mitochondria adopt donut-shaped morphologies, and live-cell imaging with two Keima-based reporters demonstrates Gal-8-induced mitophagy. ERK signaling inhibition abrogates all these Gal-8-induced mitochondrial changes and cell proliferation. Studies with established mutant versions of Gal-8 and CHO cells reveal that mitochondrial changes and proliferative response require interactions between the N-terminal carbohydrate recognition domain of Gal-8 and α-2,3-sialylated N-glycans at the cell surface. DRP1, a key regulator of mitochondrial fission, becomes phosphorylated in MDCK cells or overexpressed in RPTEC cells in an ERK-dependent manner, mediating mitochondrial fragmentation and perinuclear redistribution. Bafilomycin A abrogates Gal-8-induced cell proliferation, suggesting that mitophagy serves as an adaptation to cell proliferation demands. Functional analysis under Gal-8 stimulation shows that mitochondria maintain an active electron transport chain, partially uncoupled from ATP synthesis, and an increased membrane potential, indicative of healthy mitochondria. Meanwhile, the cells exhibit increased extracellular acidification rate and lactate production via aerobic glycolysis, a hallmark of an active proliferative state. Our findings integrate mitochondrial dynamics with metabolic adaptations during Gal-8-induced cell proliferation, with potential implications for physiology, disease, and therapeutic strategies.

Mitotic spindle membranes

The mitotic spindle, which uses microtubules (MTs) and MT-based motor proteins to separate sister chromosomes prior to cell division, contains abundant membranes, organelles, and protein assemblies derived from the familiar interphase intracellular membrane network. In this essay, mainly with reference to selected animal and fungal cells, I summarize current ideas about the reciprocal functional relationship between these mitotic spindle-associated membranes and the spindle MT cytoskeleton, in which; 1) spindle membranes control the composition, Ca++ ion concentration and mechanical performance of the spindle MT cytoskeleton; and conversely 2) the spindle MT cytoskeleton contributes to membrane/organelle partitioning and inheritance during cell division and serves as a reservoir of membranes, organelles, and vesicles for delivery to the interphase cytoplasm, plasma membrane, and cleavage furrow.

From Cell Architecture to Mitochondrial Signaling: Role of Intermediate Filaments in Health, Aging, and Disease

The coordination of cytoskeletal proteins shapes cell architectures and functions. Age-related changes in cellular mechanical properties have been linked to decreased cellular and tissue dysfunction. Studies have also found a relationship between mitochondrial function and the cytoskeleton. Cytoskeleton inhibitors impact mitochondrial quality and function, including motility and morphology, membrane potential, and respiration. The regulatory properties of the cytoskeleton on mitochondrial functions are involved in the pathogenesis of several diseases. Disassembly of the axon's cytoskeleton and the release of neurofilament fragments have been documented during neurodegeneration. However, these changes can also be related to mitochondrial impairments, spanning from reduced mitochondrial quality to altered bioenergetics. Herein, we discuss recent research highlighting some of the pathophysiological roles of cytoskeleton disassembly in aging, neurodegeneration, and neuromuscular diseases, with a focus on studies that explored the relationship between intermediate filaments and mitochondrial signaling as relevant contributors to cellular health and disease.

Antibody-Directing Antibody Conjugates (ADACs) Enabled by Orthogonal Click Chemistry for Targeted Intracellular Delivery

Using orthogonal click chemistries for efficient nanoscale self-assembly, a new antibody-directing antibody conjugate (ADAC) nanogel is generated. In this system, one of the antibodies is displayed on the nanogel surface to specifically recognize cell-surface epitopes while the other antibody is encapsulated inside the nanogel core. The system is programmed to release the latter antibody in its functional form in the cytosolic environment of a specific cell to engage intracellular targets. ADACs offer a potential solution to harness the advantages seen with antibody-drug conjugates (ADCs) to deliver therapeutic cargos to specific tissues, but with the added capability of carrying biologics as the cargo. In this manuscript, this potential is demonstrated through delivery of antibodies against intracellular targets in specific cells. This platform offers new avenues for precise therapeutic interventions and the potential to address previously "undruggable" cellular targets.

Regulation of mitochondrial structure by the actin cytoskeleton

Mitochondria are the powerhouse of the cell and play important roles in multiple cellular processes including cell metabolism, proliferation, and programmed cell death. Mitochondria are double-membrane organelles with the inner membrane folding inward to form cristae. Mitochondria networks undergo dynamic fission and fusion. Deregulation of mitochondrial structure has been linked to perturbed mitochondrial membrane potential and disrupted metabolism, as evidenced in tumorigenesis, neurodegenerative diseases, etc. Actin and its motors-myosins have long been known to generate mechanical forces and participate in short-distance cargo transport. Accumulating knowledge from biochemistry and live cell/electron microscope imaging has demonstrated the role of actin filaments in pre-constricting the mitochondria during fission. Recent studies have suggested the involvement of myosins in cristae maintenance and mitochondria quality control. Here, we review current findings and discuss future directions in the emerging fields of cytoskeletal regulation in cristae formation, mitochondrial dynamics, intracellular transport, and mitocytosis, with focus on the actin cytoskeleton and its motor proteins.

Biogenesis, inheritance, and 3D ultrastructure of the microsporidian mitosome

During the reductive evolution of obligate intracellular parasites called microsporidia, a tiny remnant mitochondrion (mitosome) lost its typical cristae, organellar genome, and most canonical functions. Here, we combine electron tomography, stereology, immunofluorescence microscopy, and bioinformatics to characterise mechanisms of growth, division, and inheritance of this minimal mitochondrion in two microsporidia species (grown within a mammalian RK13 culture-cell host). Mitosomes of Encephalitozoon cuniculi (2-12/cell) and Trachipleistophora hominis (14-18/nucleus) displayed incremental/non-phasic growth and division and were closely associated with an organelle identified as equivalent to the fungal microtubule-organising centre (microsporidian spindle pole body; mSPB). The mitosome-mSPB association was resistant to treatment with microtubule-depolymerising drugs nocodazole and albendazole. Dynamin inhibitors (dynasore and Mdivi-1) arrested mitosome division but not growth, whereas bioinformatics revealed putative dynamins Drp-1 and Vps-1, of which, Vps-1 rescued mitochondrial constriction in dynamin-deficient yeast (Schizosaccharomyces pombe). Thus, microsporidian mitosomes undergo incremental growth and dynamin-mediated division and are maintained through ordered inheritance, likely mediated via binding to the microsporidian centrosome (mSPB).

Xanthene, cyanine, oxazine and BODIPY: the four pillars of the fluorophore empire for super-resolution bioimaging

In the realm of biological research, the invention of super-resolution microscopy (SRM) has enabled the visualization of ultrafine sub-cellular structures and their functions in live cells at the nano-scale level, beyond the diffraction limit, which has opened up a new window for advanced biomedical studies to unravel the complex unknown details of physiological disorders at the sub-cellular level with unprecedented resolution and clarity. However, most of the SRM techniques are highly reliant on the personalized special photophysical features of the fluorophores. In recent times, there has been an unprecedented surge in the development of robust new fluorophore systems with personalized features for various super-resolution imaging techniques. To date, xanthene, cyanine, oxazine and BODIPY cores have been authoritatively utilized as the basic fluorophore units in most of the small-molecule-based organic fluorescent probe designing strategies for SRM owing to their excellent photophysical characteristics and easy synthetic acquiescence. Since the future of next-generation SRM studies will be decided by the availability of advanced fluorescent probes and these four fluorescent building blocks will play an important role in progressive new fluorophore design, there is an urgent need to review the recent advancements in designing fluorophores for different SRM methods based on these fluorescent dye cores. This review article not only includes a comprehensive discussion about the recent developments in designing fluorescent probes for various SRM techniques based on these four important fluorophore building blocks with special emphasis on their effective integration into live cell super-resolution bio-imaging applications but also critically evaluates the background of each of the fluorescent dye cores to highlight their merits and demerits towards developing newer fluorescent probes for SRM.

Vesicle-mediated transport of ALIX and ESCRT-III to the intercellular bridge during cytokinesis

Cellular abscission is the final step of cytokinesis that leads to the physical separation of the two daughter cells. The scaffold protein ALIX and the ESCRT-I protein TSG101 contribute to recruiting ESCRT-III to the midbody, which orchestrates the final membrane scission of the intercellular bridge. Here, we addressed the transport mechanisms of ALIX and ESCRT-III subunit CHMP4B to the midbody. Structured illumination microscopy revealed gradual accumulation of ALIX at the midbody, resulting in the formation of spiral-like structures extending from the midbody to the abscission site, which strongly co-localized with CHMP4B. Live-cell microscopy uncovered that ALIX appeared together with CHMP4B in vesicular structures, whose motility was microtubule-dependent. Depletion of ALIX led to structural alterations of the midbody and delayed recruitment of CHMP4B, resulting in delayed abscission. Likewise, depletion of the kinesin-1 motor KIF5B reduced the motility of ALIX-positive vesicles and delayed midbody recruitment of ALIX, TSG101 and CHMP4B, accompanied by impeded abscission. We propose that ALIX, TSG101 and CHMP4B are associated with endosomal vesicles transported on microtubules by kinesin-1 to the cytokinetic bridge and midbody, thereby contributing to their function in abscission.

Mitocytosis Is Critical for Phthalate-Induced Injury to the Ovarian Granulosa Cell Layer in Quail (Coturnix japonica)

Phthalates are widely used synthetic chemicals that determine endocrine disruption effects on female reproductivity and oviposition. Our study demonstrated that the mitochondrial quality in ovarian granulosa cells (GCs) is associated with a poor prognosis in female reproduction. However, the molecular mechanism of di-(2-ethylhexyl) phthalate (DEHP) exposure on the quail ovarian GC layer is still unknown. To validate the effects of DEHP on the GC layer, 8 days' old 150 female Japanese quail were treated orally with DEHP (250, 500, and 750 mg/kg BW/day) for 45 days to explore the toxic effects of DEHP on the ovarian GC layer. Histopathological assessment and ultrastructure observation found that DEHP decreased the thickness of the GC layer, resulted in mitochondrial damage, and activated mitocytosis. Additionally, the results further suggested that DEHP impacted the secretion of steroid hormones (reduced FSH, E2, and T levels and boosted Prog, PRL, and LH levels) by triggering mitocytosis (enhanced transcription of MYO19 and protein of KIF5B levels), mitochondrial dynamics (increasing mRNA and protein levels of OPA1, DRP1, MFN1, and MFN2), mitophagy (increasing mRNA and protein levels of Parkin, LC3B, and P62), and inducing GC function disorder. In conclusion, our research provided a new idea to explain the mechanism of DEHP toxicity of the ovarian GC layer in quail and presented insights into the role of mitocytosis in DEHP-induced ovarian GC layer injury.

Mitochondria in reproduction

In reproduction, mitochondria produce bioenergy, help to synthesize biomolecules, and support the ovaries, oogenesis, and preimplantation embryos, thereby facilitating healthy live births. However, the regulatory mechanism of mitochondria in oocytes and embryos during oogenesis and embryo development has not been clearly elucidated. The functional activity of mitochondria is crucial for determining the quality of oocytes and embryos; therefore, the underlying mechanism must be better understood. In this review, we summarize the specific role of mitochondria in reproduction in oocytes and embryos. We also briefly discuss the recovery of mitochondrial function in gametes and zygotes. First, we introduce the general characteristics of mitochondria in cells, including their roles in adenosine triphosphate and reactive oxygen species production, calcium homeostasis, and programmed cell death. Second, we present the unique characteristics of mitochondria in female reproduction, covering the bottleneck theory, mitochondrial shape, and mitochondrial metabolic pathways during oogenesis and preimplantation embryo development. Mitochondrial dysfunction is associated with ovarian aging, a diminished ovarian reserve, a poor ovarian response, and several reproduction problems in gametes and zygotes, such as aneuploidy and genetic disorders. Finally, we briefly describe which factors are involved in mitochondrial dysfunction and how mitochondrial function can be recovered in reproduction. We hope to provide a new viewpoint regarding factors that can overcome mitochondrial dysfunction in the field of reproductive medicine.

Doublecortin and JIP3 are neural-specific counteracting regulators of dynein-mediated retrograde trafficking

Mutations in the microtubule (MT)-binding protein doublecortin (DCX) or in the MT-based molecular motor dynein result in lissencephaly. However, a functional link between DCX and dynein has not been defined. Here, we demonstrate that DCX negatively regulates dynein-mediated retrograde transport in neurons from Dcx-/y or Dcx-/y;Dclk1-/- mice by reducing dynein's association with MTs and disrupting the composition of the dynein motor complex. Previous work showed an increased binding of the adaptor protein C-Jun-amino-terminal kinase-interacting protein 3 (JIP3) to dynein in the absence of DCX. Using purified components, we demonstrate that JIP3 forms an active motor complex with dynein and its cofactor dynactin with two dyneins per complex. DCX competes with the binding of the second dynein, resulting in a velocity reduction of the complex. We conclude that DCX negatively regulates dynein-mediated retrograde transport through two critical interactions by regulating dynein binding to MTs and regulating the composition of the dynein motor complex.

Hubbing the Cancer Cell

Oncogenic transformation drives adaptive changes in a growing tumor that affect the cellular organization of cancerous cells, resulting in the loss of specialized cellular functions in the polarized compartmentalization of cells. The resulting altered metabolic and morphological patterns are used clinically as diagnostic markers. This review recapitulates the known functions of actin, microtubules and the γ-tubulin meshwork in orchestrating cell metabolism and functional cellular asymmetry.

How cytoskeletal proteins regulate mitochondrial energetics in cell physiology and diseases

Mitochondria are ubiquitous organelles that play a pivotal role in the supply of energy through the production of adenosine triphosphate in all eukaryotic cells. The importance of mitochondria in cells is demonstrated in the poor survival outcomes observed in patients with defects in mitochondrial gene or RNA expression. Studies have identified that mitochondria are influenced by the cell's cytoskeletal environment. This is evident in pathological conditions such as cardiomyopathy where the cytoskeleton is in disarray and leads to alterations in mitochondrial oxygen consumption and electron transport. In cancer, reorganization of the actin cytoskeleton is critical for trans-differentiation of epithelial-like cells into motile mesenchymal-like cells that promotes cancer progression. The cytoskeleton is critical to the shape and elongation of neurons, facilitating communication during development and nerve signalling. Although it is recognized that cytoskeletal proteins physically tether mitochondria, it is not well understood how cytoskeletal proteins alter mitochondrial function. Since end-stage disease frequently involves poor energy production, understanding the role of the cytoskeleton in the progression of chronic pathology may enable the development of therapeutics to improve energy production and consumption and slow disease progression.

This article is part of the theme issue ‘The cardiomyocyte: new revelations on the interplay between architecture and function in growth, health, and disease’.

Dominantly acting KIF5B variants with pleiotropic cellular consequences cause variable clinical phenotypes

Kinesins are motor proteins involved in microtubule (MT)-mediated intracellular transport. They contribute to key cellular processes, including intracellular trafficking, organelle dynamics and cell division. Pathogenic variants in kinesin-encoding genes underlie several human diseases characterized by an extremely variable clinical phenotype, ranging from isolated neurodevelopmental/neurodegenerative disorders to syndromic phenotypes belonging to a family of conditions collectively termed as 'ciliopathies.' Among kinesins, kinesin-1 is the most abundant MT motor for transport of cargoes towards the plus end of MTs. Three kinesin-1 heavy chain isoforms exist in mammals. Different from KIF5A and KIF5C, which are specifically expressed in neurons and established to cause neurological diseases when mutated, KIF5B is an ubiquitous protein. Three de novo missense KIF5B variants were recently described in four subjects with a syndromic skeletal disorder characterized by kyphomelic dysplasia, hypotonia and DD/ID. Here, we report three dominantly acting KIF5B variants (p.Asn255del, p.Leu498Pro and p.Leu537Pro) resulting in a clinically wide phenotypic spectrum, ranging from dilated cardiomyopathy with adult-onset ophthalmoplegia and progressive skeletal myopathy to a neurodevelopmental condition characterized by severe hypotonia with or without seizures. In vitro and in vivo analyses provide evidence that the identified disease-associated KIF5B variants disrupt lysosomal, autophagosome and mitochondrial organization, and impact cilium biogenesis. All variants, and one of the previously reported missense changes, were shown to affect multiple developmental processes in zebrafish. These findings document pleiotropic consequences of aberrant KIF5B function on development and cell homeostasis, and expand the phenotypic spectrum resulting from altered kinesin-mediated processes.

Le transport mitochondrial

La reprogrammation métabolique est l’un des marqueurs de la carcinogenèse. Au cœur de cette reprogrammation se trouvent les mitochondries qui produisent l’énergie sous forme de molécules d’ATP. La régulation spatio-temporelle de la production d’ATP, indispensable pour fournir l’énergie au bon endroit et au bon moment, est assurée par le transport intracellulaire des mitochondries. Les complexes Miro/TRAK présents à la surface des mitochondries se lient aux protéines motrices de la cellule (dynéine, kinésine, myosine) pour transporter les mitochondries le long du cytosquelette. Ces acteurs du transport mitochondrial sont souvent dérégulés dans le cancer. Nous présentons dans cette revue les mécanismes par lesquels le transport mitochondrial contribue à la migration, à la division cellulaire et à la réponse au stress des cellules cancéreuses. Décrypter ces mécanismes pourrait ouvrir la voie à de nouvelles approches thérapeutiques en oncologie.

Mitochondria Lead the Way: Mitochondrial Dynamics and Function in Cellular Movements in Development and Disease

The dynamics, distribution and activity of subcellular organelles are integral to regulating cell shape changes during various physiological processes such as epithelial cell formation, cell migration and morphogenesis. Mitochondria are famously known as the powerhouse of the cell and play an important role in buffering calcium, releasing reactive oxygen species and key metabolites for various activities in a eukaryotic cell. Mitochondrial dynamics and morphology changes regulate these functions and their regulation is, in turn, crucial for various morphogenetic processes. In this review, we evaluate recent literature which highlights the role of mitochondrial morphology and activity during cell shape changes in epithelial cell formation, cell division, cell migration and tissue morphogenesis during organism development and in disease. In general, we find that mitochondrial shape is regulated for their distribution or translocation to the sites of active cell shape dynamics or morphogenesis. Often, key metabolites released locally and molecules buffered by mitochondria play crucial roles in regulating signaling pathways that motivate changes in cell shape, mitochondrial shape and mitochondrial activity. We conclude that mechanistic analysis of interactions between mitochondrial morphology, activity, signaling pathways and cell shape changes across the various cell and animal-based model systems holds the key to deciphering the common principles for this interaction.

The Multifaceted Regulation of Mitochondrial Dynamics During Mitosis

Mitosis ensures genome integrity by mediating precise segregation of the duplicated genetic material. Segregation of subcellular organelles during mitosis also needs to be tightly coordinated in order to warrant their proper inheritance and cellular homeostasis. The inheritance of mitochondria, a powerhouse of the cell, is tightly regulated in order to meet the high energy demand to fuel the mitotic machinery. Mitochondria are highly dynamic organelles, which undergo events of fission, fusion and transport during different cell cycle stages. Importantly, during mitosis several kinases phosphorylate the key mitochondrial factors and drive fragmentation of mitochondria to allow for their efficient distribution and inheritance to two daughter cells. Recent evidence suggests that mitochondrial fission can also actively contribute to the regulation of mitotic progression. This review aims at summarizing established and emerging concepts about the complex regulatory networks which couple crucial mitotic factors and events to mitochondrial dynamics and which could be implicated in human disease.

A coarse-grained NADH redox model enables inference of subcellular metabolic fluxes from fluorescence lifetime imaging

Mitochondrial metabolism is of central importance to diverse aspects of cell and developmental biology. Defects in mitochondria are associated with many diseases, including cancer, neuropathology, and infertility. Our understanding of mitochondrial metabolism in situ and dysfunction in diseases are limited by the lack of techniques to measure mitochondrial metabolic fluxes with sufficient spatiotemporal resolution. Herein, we developed a new method to infer mitochondrial metabolic fluxes in living cells with subcellular resolution from fluorescence lifetime imaging of NADH. This result is based on the use of a generic coarse-grained NADH redox model. We tested the model in mouse oocytes and human tissue culture cells subject to a wide variety of perturbations by comparing predicted fluxes through the electron transport chain (ETC) to direct measurements of oxygen consumption rate. Interpreting the fluorescence lifetime imaging microscopy measurements of NADH using this model, we discovered a homeostasis of ETC flux in mouse oocytes: perturbations of nutrient supply and energy demand of the cell do not change ETC flux despite significantly impacting NADH metabolic state. Furthermore, we observed a subcellular spatial gradient of ETC flux in mouse oocytes and found that this gradient is primarily a result of a spatially heterogeneous mitochondrial proton leak. We concluded from these observations that ETC flux in mouse oocytes is not controlled by energy demand or supply, but by the intrinsic rates of mitochondrial respiration.

Physical bioenergetics: Energy fluxes, budgets, and constraints in cells

Cells are the basic units of all living matter which harness the flow of energy to drive the processes of life. While the biochemical networks involved in energy transduction are well-characterized, the energetic costs and constraints for specific cellular processes remain largely unknown. In particular, what are the energy budgets of cells? What are the constraints and limits energy flows impose on cellular processes? Do cells operate near these limits, and if so how do energetic constraints impact cellular functions? Physics has provided many tools to study nonequilibrium systems and to define physical limits, but applying these tools to cell biology remains a challenge. Physical bioenergetics, which resides at the interface of nonequilibrium physics, energy metabolism, and cell biology, seeks to understand how much energy cells are using, how they partition this energy between different cellular processes, and the associated energetic constraints. Here we review recent advances and discuss open questions and challenges in physical bioenergetics.

Mitochondrial dynamics, positioning and function mediated by cytoskeletal interactions

The ability of a mitochondrion to undergo fission and fusion, and to be transported and localized within a cell are central not just to proper functioning of mitochondria, but also to that of the cell. The cytoskeletal filaments, namely microtubules, F-actin and intermediate filaments, have emerged as prime movers in these dynamic mitochondrial shape and position transitions. In this review, we explore the complex relationship between the cytoskeleton and the mitochondrion, by delving into: (i) how the cytoskeleton helps shape mitochondria via fission and fusion events, (ii) how the cytoskeleton facilitates the translocation and anchoring of mitochondria with the activity of motor proteins, and (iii) how these changes in form and position of mitochondria translate into functioning of the cell.

Motor proteins at the mitochondria-cytoskeleton interface

Mitochondria are multifunctional organelles that not only produce energy for the cell, but are also important for cell signalling, apoptosis and many biosynthetic pathways. In most cell types, they form highly dynamic networks that are constantly remodelled through fission and fusion events, repositioned by motor-dependent transport and degraded when they become dysfunctional. Motor proteins and their tracks are key regulators of mitochondrial homeostasis, and in this Review, we discuss the diverse functions of the three classes of motor proteins associated with mitochondria - the actin-based myosins, as well as the microtubule-based kinesins and dynein. In addition, Miro and TRAK proteins act as adaptors that link kinesin-1 and dynein, as well as myosin of class XIX (MYO19), to mitochondria and coordinate microtubule- and actin-based motor activities. Here, we highlight the roles of motor proteins and motor-linked track dynamics in the transporting and docking of mitochondria, and emphasize their adaptations in specialized cells. Finally, we discuss how motor-cargo complexes mediate changes in mitochondrial morphology through fission and fusion, and how they modulate the turnover of damaged organelles via quality control pathways, such as mitophagy. Understanding the importance of motor proteins for mitochondrial homeostasis will help to elucidate the molecular basis of a number of human diseases.

Cyanine mitochondrial dye with slightly selective cytotoxicity against A549 cancerous cells

Delocalized lipophilic cations (DLCs) are known as mitochondria-addressed molecules. Mitochondria targeting may provide opportunities for tumor detection. DLCs may have antioxidant or anticancer properties. In this study, we focused on the toxicity and localization of 2-[(E)-2-(5-fluoro-2-methyl-1H-indol-3-yl)ethenyl]-1,6-dimethylpyridin-1-ium iodide (62E2), which has recently been found as a novel cytotoxic fluorescent compound. The excitation maximum of 62E2 is 452 ± 10 nm and its emission maximum is 579 ± 10 nm. It is accumulated in the cells and stains mitochondria in nanomolar concentrations. 62E2 is cytotoxic and mitotoxic in low micromolar concentrations, and it demonstrates some selectivity of cytotoxicity against A549 cancer cells. The closest analog of 62E2 is F16, which is the fluorescent mitotoxic agent that has been described earlier as a potential anticancer agent. We hope that 62E2 described here is useful in expanding the diversity of cyanine fluorescent mitochondrial dyes and the analysis of their structure-activity relationships.

Wnt5a regulates Ameloblastoma Cell Migration by modulating Mitochondrial and Cytoskeletal Dynamics

Objective: Abnormal expression of Wnt5a has been detected in various tumors, including ameloblastoma (AB). Yet, there is no specific mechanistic evidence for the functional role of Wnt5a in AB. In this study, we aimed to conduct a mechanistic examination of the importance of Wnt5a in AB development. Methods: The expressions of Wnt5a and Coro1A were examined by Western blot and immunohistochemistry both in AB tissues and AM-1 cells. The number and size of mitochondria were detected by electronic transmission microscope and confocal microscope. Gain-of-function and loss-of-function assays were used to explore the biological roles of Wnt5a and Coro1A in organelle dynamics changes and cell migration. Cell migration was detected by wound healing and transwell assay. Results: We found that in AM-1 cells, up-regulation of Wnt5a led to enhanced mitochondrial energy production and altered calcium homeostasis, with elevated calcium levels directly leading to altered mitochondrial dynamics and interactions between the cytoskeleton and the mitochondria. When Wnt5a or its downstream cytoskeleton-associated protein Coro1A was knocked down, the migration capacity of AM-1 cells was markedly impaired. Conclusion: Together, these results suggest that Wnt5a plays mitochondria and cytoskeleton specific roles in regulating the development of human AB, with its down-regulation leading to impaired tumor development, thus highlighting Wnt5a or Coro1A as potentially viable therapeutic targets for the treatment of AB.

Mitochondrial Inheritance in Phytopathogenic Fungi-Everything Is Known, or Is It?

Mitochondria are important organelles in eukaryotes that provide energy for cellular processes. Their function is highly conserved and depends on the expression of nuclear encoded genes and genes encoded in the organellar genome. Mitochondrial DNA replication is independent of the replication control of nuclear DNA and as such, mitochondria may behave as selfish elements, so they need to be controlled, maintained and reliably inherited to progeny. Phytopathogenic fungi meet with special environmental challenges within the plant host that might depend on and influence mitochondrial functions and services. We find that this topic is basically unexplored in the literature, so this review largely depends on work published in other systems. In trying to answer elemental questions on mitochondrial functioning, we aim to introduce the aspect of mitochondrial functions and services to the study of plant-microbe-interactions and stimulate phytopathologists to consider research on this important organelle in their future projects.

Light Microscopy of Mitochondria at the Nanoscale

Mitochondria are essential for eukaryotic life. These double-membrane organelles often form highly dynamic tubular networks interacting with many cellular structures. Their highly convoluted contiguous inner membrane compartmentalizes the organelle, which is crucial for mitochondrial function. Since the diameter of the mitochondrial tubules is generally close to the diffraction limit of light microscopy, it is often challenging, if not impossible, to visualize submitochondrial structures or protein distributions using conventional light microscopy. This renders super-resolution microscopy particularly valuable, and attractive, for studying mitochondria. Super-resolution microscopy encompasses a diverse set of approaches that extend resolution, as well as nanoscopy techniques that can even overcome the diffraction limit. In this review, we provide an overview of recent studies using super-resolution microscopy to investigate mitochondria, discuss the strengths and opportunities of the various methods in addressing specific questions in mitochondrial biology, and highlight potential future developments.

Mitochondria in early development: linking the microenvironment, metabolism and the epigenome

Mitochondria, originally of bacterial origin, are highly dynamic organelles that have evolved a symbiotic relationship within eukaryotic cells. Mitochondria undergo dynamic, stage-specific restructuring and redistribution during oocyte maturation and preimplantation embryo development, necessary to support key developmental events. Mitochondria also fulfil a wide range of functions beyond ATP synthesis, including the production of intracellular reactive oxygen species and calcium regulation, and are active participants in the regulation of signal transduction pathways. Communication between not only mitochondria and the nucleus, but also with other organelles, is emerging as a critical function which regulates preimplantation development. Significantly, perturbations and deficits in mitochondrial function manifest not only as reduced quality and/or poor oocyte and embryo development but contribute to post-implantation failure, long-term cell function and adult disease. A growing body of evidence indicates that altered availability of metabolic co-factors modulate the activity of epigenetic modifiers, such that oocyte and embryo mitochondrial activity and dynamics have the capacity to establish long-lasting alterations to the epigenetic landscape. It is proposed that preimplantation embryo development may represent a sensitive window during which epigenetic regulation by mitochondria is likely to have significant short- and long-term effects on embryo, and offspring, health. Hence, mitochondrial integrity, communication and metabolism are critical links between the environment, the epigenome and the regulation of embryo development.

Association Between Functional Activity of Mitochondria and Actin Cytoskeleton Instability in Oocytes from Advanced Age Mice

Mitochondrial dysfunction is strongly associated with the oocyte quality and aging, wherein the aged oocytes are related to the actin cytoskeleton integrity; however, whether this integrity is associated with mitochondrial dysfunction in oocytes from aged mice remains unclear. In the present study, we investigated the relationship between mitochondrial dysfunction and actin cytoskeleton instability in oocytes from the aged mice. We performed comparable analysis of mitochondrial motility between young, 1.5 μM cytochalasin B (CB)-treated young oocytes, and aged oocytes by confocal live imaging. Moreover, we analyzed the relationships between mitochondrial motility and maturation ratios, including ATP production ratio of the young, CB-treated young, and aged oocytes. Actin cytoskeleton instability in the aged oocytes and CB-treated young oocytes led to a significant decrease in the mitochondrial motility and low ATP productive ratios compared to those in the young group. Our data suggest that the actin cytoskeleton instability is presumably the primary cause for the loss of mitochondrial function in the aged murine oocytes.

Ezrin Orchestrates Signal Transduction in Airway Cells

Ezrin is a critical structural protein that organizes receptor complexes and orchestrates their signal transduction. In this study, we review the ezrin-meditated regulation of critical receptor complexes, including the epidermal growth factor receptor (EGFR), CD44, vascular cell adhesion molecule (VCAM), and the deleted in colorectal cancer (DCC) receptor. We also analyze the ezrin-meditated regulation of critical pathways associated with asthma, such as the RhoA, Rho-associated protein kinase (ROCK), and protein kinase A (cAMP/PKA) pathways. Mounting evidence suggests that ezrin plays a role in controlling airway cell function and potentially contributes to respiratory diseases. Ezrin can participate in asthma pathogenesis by affecting bronchial epithelium repair, T lymphocyte regulation, and the contraction of the airway smooth muscle cells. These studies provide new insights for the design of novel therapeutic strategies for asthma treatment.

GBF1 and Arf1 interact with Miro and regulate mitochondrial positioning within cells

The spatial organization of cells depends on coordination between cytoskeletal systems and intracellular organelles. The Arf1 small G protein and its activator GBF1 are important regulators of Golgi organization, maintaining its morphology and function. Here we show that GBF1 and its substrate Arf1 regulate the spatial organization of mitochondria in a microtubule-dependent manner. Miro is a mitochondrial membrane protein that interacts through adaptors with microtubule motor proteins such as cytoplasmic dynein, the major microtubule minus end directed motor. We demonstrate a physical interaction between GBF1 and Miro, and also between the active GTP-bound form of Arf1 and Miro. Inhibition of GBF1, inhibition of Arf1 activation, or overexpression of Miro, caused a collapse of the mitochondrial network towards the centrosome. The change in mitochondrial morphology upon GBF1 inhibition was due to a two-fold increase in the time engaged in retrograde movement compared to control conditions. Electron tomography revealed that GBF1 inhibition also resulted in larger mitochondria with more complex morphology. Miro silencing or drug inhibition of cytoplasmic dynein activity blocked the GBF1-dependent repositioning of mitochondria. Our results show that blocking GBF1 function promotes dynein- and Miro-dependent retrograde mitochondrial transport along microtubules towards the microtubule-organizing center, where they form an interconnected network.

Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair

Cytokinesis and single-cell wound repair both involve contractile assemblies of filamentous actin (F-actin) and myosin II organized into characteristic ring-like arrays. The assembly of these actomyosin contractile rings (CRs) is specified spatially and temporally by small Rho GTPases, which trigger local actin polymerization and myosin II contractility via a variety of downstream effectors. We now have a much clearer view of the Rho GTPase signaling cascade that leads to the formation of CRs, but some factors involved in CR positioning, assembly, and function remain poorly understood. Recent studies show that this regulation is multifactorial and goes beyond the long-established Ca²⁺ -dependent processes. There is substantial evidence that the Ca²⁺ -independent changes in cell shape, tension, and plasma membrane composition that characterize cytokinesis and single-cell wound repair also regulate CR formation. Elucidating the regulation and mechanistic properties of CRs is important to our understanding of basic cell biology and holds potential for therapeutic applications in human disease. In this review, we present a primer on the factors influencing and regulating CR positioning, assembly, and contraction as they occur in a variety of cytokinetic and single-cell wound repair models. Anat Rec, 301:2051-2066, 2018. © 2018 Wiley Periodicals, Inc.

Mitochondria-Specific Monoclonal Antibodies in Eggs and Embryos of the Ascidian Halocynthia roretzi

Ascidian embryos have become an important model for embryological studies, offering a simple example for mechanisms of cytoplasmic components segregation. It is a well-known example that the asymmetric segregation of mitochondria into muscle lineage cells occurs during ascidian embryogenesis. However, it is still unclear which signaling pathway is involved in this process. To obtain molecular markers for studying mechanisms involved in the asymmetric distribution of mitochondria, we have produced monoclonal antibodies, Mito-1, Mito-2 and Mito-3, that specifically recognize mitochondriarich cytoplasm in cells of the ascidian Halocynthia roretzi embryos. These antibodies stained cytoplasm like reticular structure in epidermis cells, except for nuclei, at the early tailbud stage. Similar pattern was observed in vital staining of mitochondria with DiOC2, a fluorescent probe of mitochondria. Immunostaining with these antibodies showed that mitochondria are evenly distributed in the animal hemisphere blastomeres at cleavage stages, whereas not in the vegetal hemisphere blastomeres. Mitochondria were transferred to the presumptive muscle and nerve cord lineage cells of the marginal zone in the vegetal hemisphere more than to the presumptive mesenchyme, notochord and endoderm lineage of the central zone. Therefore, it is suggested that these antibodies will be useful markers for studying mechanisms involved in the polarized distribution of mitochondria during ascidian embryogenesis.

Cancer is an adaptation that selects in animals against energy dissipation

As cancer usually follows reproduction, it is generally assumed that cancer does not select. Graham has however argued that juvenile cancer, which precedes reproduction, could during evolution have implemented a "cancer selection" that resulted in novel traits that suppress this juvenile cancer; an example is protection against UV sunlight-induced cancer, required for the emergence of terrestrial animals from the sea. We modify the cancer selection mechanism to the posited "cancer adaptation" mechanism, in which juvenile mortality is enhanced through the diminished care received by juveniles from their (grand) parents when these suffer from cancer in old age. Moreover, it is posited that the cancer adaptation selects against germline "dissipative genes", genes that result in enhanced free energy dissipation. Cancer's progression is interpreted as a cascade at increasing scale of repeated amplification of energy dissipation, a cascade involving heat shock, the Warburg effect, the cytokine IL-6, tumours, and hypermetabolism. Disturbance of any physiological process must enhance energy dissipation if the animal remains functioning normally, what explains multicausality, why "everything gives you cancer". The hypothesis thus comprises two newly invoked partial processes-diminished (grand) parental care and dissipation amplification-and results in a "selection against enhanced energy dissipation" which gives during evolution the benefit of energy conservation. Due to this benefit, cancer would essentially be an adaptation, and not a genetic disease, as assumed in the "somatic mutation theory". Cancer by somatic mutations is only a side process. The cancer adaptation hypothesis is substantiated by (1) cancer's extancy, (2) the failure of the somatic mutation theory, (3) cancer's initiation by a high temperature, (4) the interpretation of cancer's progression as a thermal process, and (5) the interpretation of tumours as organs that implement thermogenesis. The hypothesis could in principle be verified by monitoring in a population over several generations (1) the presence of dissipative genes, (2) the incidence of cancer, and (3) the beneficial effect of dissipative gene removal by cancer on starvation/famine survival.

Deletion of RhoA in Progesterone Receptor-Expressing Cells Leads to Luteal Insufficiency and Infertility in Female Mice

Ras homolog gene family, member A (RhoA) is widely expressed throughout the female reproductive system. To assess its role in progesterone receptor-expressing cells, we generated RhoA conditional knockout mice RhoAd/d (RhoAf/f-Pgr-Cre+/-). RhoAd/d female mice had comparable mating activity, serum luteinizing hormone, prolactin, and estradiol levels and ovulation with control but were infertile with progesterone insufficiency, indicating impaired steroidogenesis in RhoAd/d corpus luteum (CL). RhoA was highly expressed in wild-type luteal cells and conditionally deleted in RhoAd/d CL. Gestation day 3.5 (D3.5) RhoAd/d ovaries had reduced numbers of CL, less defined corpus luteal cord formation, and disorganized CL collagen IV staining. RhoAd/d CL had lipid droplet and free cholesterol accumulation, indicating the availability of cholesterol for steroidogenesis, but disorganized β-actin and vimentin staining, indicating disrupted cytoskeleton integrity. Cytoskeleton is important for cytoplasmic cholesterol movement to mitochondria and for regulating mitochondria. Dramatically reduced expression of mitochondrial markers heat shock protein 60 (HSP60), voltage-dependent anion channel, and StAR was detected in RhoAd/d CL. StAR carries out the rate-limiting step of steroidogenesis. StAR messenger RNA expression was reduced in RU486-treated D3.5 wild-type CL and tended to be induced in progesterone-treated D3.5 RhoAd/d CL, with parallel changes of HSP60 expression. These data demonstrated the in vivo function of RhoA in CL luteal cell cytoskeleton integrity, cholesterol transport, StAR expression, and progesterone synthesis, and a positive feedback on StAR expression in CL by progesterone signaling. These findings provide insights into mechanisms of progesterone insufficiency.

Phosphorylation-Induced Motor Shedding Is Required at Mitosis for Proper Distribution and Passive Inheritance of Mitochondria

While interphase mitochondria associate with microtubules, mitotic mitochondria dissociate from spindle microtubules and localize in the cell periphery. Here, we show that this redistribution is not mediated by mitochondrial active transport or tethering to the cytoskeleton. Instead, kinesin and dynein, which link mitochondria to microtubules, are shed from the mitochondrial surface. Shedding is driven by phosphorylation of mitochondrial and cytoplasmic targets by CDK1 and Aurora A. Forced recruitment of motor proteins to mitotic mitochondria to override this shedding prevents their proper symmetrical distribution and disrupts the balanced inheritance of mitochondria to daughter cells. Moreover, when mitochondria with bound dynein bind to the mitotic spindle, they arrest cell-cycle progression and produce binucleate cells. Thus, our results show that the regulated release of motor proteins from the mitochondrial surface is a critical mitotic event.