Ensembles of human myosin-19 bound to calmodulin and regulatory light chain RLC12B drive multimicron transport

Beyond static snapshots: Mitochondria in action

Mitochondria are dynamic organelles essential for cellular homeostasis, undergoing continuous fission and fusion processes that regulate their morphology, distribution, and function. Disruptions in these dynamics are linked to numerous diseases, including neurodegenerative disorders and cancer. Understanding these processes is vital for developing therapeutic strategies aimed at mitigating mitochondrial dysfunction. This review provides an overview of recent perspectives on mitochondrial dynamics, focusing on the need for live video microscopy imaging in order to fully understand mitochondrial phenotypes and pathology. Advanced imaging tools, such as machine learning-based segmentation and label-free microscopy approaches, have the potential to transform our ability to study mitochondrial dynamics in live cells.

Myosin-1C differentially displaces tropomyosin isoforms altering their inhibition of motility

Force generation and motility by actomyosin in nonmuscle cells are spatially regulated by ∼40 tropomyosin (Tpm) isoforms. The means by which Tpms are targeted to specific cellular regions and the mechanisms that result in differential activity of myosin paralogs are unknown. We show that Tpm3.1 and Tpm1.7 inhibit Myosin-IC (Myo1C), with Tpm1.7 more effectively reducing the number of gliding filaments than Tpm3.1. Strikingly, cosedimentation and fluorescence microscopy assays revealed that Tpm3.1 is displaced from actin by Myo1C and not by myosin-II. In contrast, Tpm1.7 is only weakly displaced by Myo1C. Unlike other characterized myosins, Myo1C motility is inhibited by Tpm when the Tpm-actin filament is activated by myosin-II. These results point to a mechanism for the exclusion of myosin-I paralogs from cellular Tpm-decorated actin filaments that are activated by other myosins. Additionally, our results suggest a potential mechanism for myosin-induced Tpm sorting in cells.

Mitochondrially-associated actin waves maintain organelle homeostasis and equitable inheritance

First identified in dividing cells as revolving clusters of actin filaments, these are now understood as mitochondrially-associated actin waves that are active throughout the cell cycle. These waves are formed from the polymerization of actin onto a subset of mitochondria. Within minutes, this F-actin depolymerizes while newly formed actin filaments assemble onto neighboring mitochondria. In interphase, actin waves locally fragment the mitochondrial network, enhancing mitochondrial content mixing to maintain organelle homeostasis. In dividing cells actin waves spatially mix mitochondria in the mother cell to ensure equitable partitioning of these organelles between daughter cells. Progress has been made in understanding the consequences of actin cycling as well as the underlying molecular mechanisms, but many questions remain, and here we review these elements. Also, we draw parallels between mitochondrially-associated actin cycling and cortical actin waves. These dynamic systems highlight the remarkable plasticity of the actin cytoskeleton.

Bisphenol S impairs mitochondrial function by targeting Myo19/oxidative phosphorylation pathway contributing to axonal and dendritic injury

Exposure to bisphenol S (BPS) is known to adversely affect neuronal development. As pivotal components of neuronal polarization, axons and dendrites are indispensable structures within neurons, crucial for the maintenance of nervous system function. Here, we investigated the impact of BPS exposure on axonal and dendritic development both in vivo and in vitro. Our results revealed that exposure to BPS during pregnancy and lactation led to a reduction in the complexity, density, and length of axons and dendrites in the prefrontal cortex (PFC) of offspring. Employing RNA sequencing technology to elucidate the underlying mechanisms of axonal and dendritic damage induced by BPS, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis highlighted a significant alteration in the oxidative phosphorylation (OXPHOS) pathway, essential for mitochondrial function. Subsequent experiments demonstrate BPS-induced impairment in mitochondrial function, including damaged morphology, decreased adenosine triphosphate (ATP) and superoxide dismutase (SOD) levels, and increased reactive oxygen species and malondialdehyde (MDA). These alterations coincided with the downregulated expression of OXPHOS pathway-related genes (ATP6V1B1, ATP5K, NDUFC1, NDUFC2, NDUFA3, COX6B1) and Myosin 19 (Myo19). Notably, Myo19 overexpression restored the BPS-induced mitochondrial dysfunction by alleviating the inhibition of OXPHOS pathway. Consequently, this amelioration was associated with a reduction in BPS-induced axonal and dendritic injury observed in cultured neurons of the PFC.

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.

Mitochondrial transport in neurons and evidence for its involvement in acute neurological disorders

Ensuring mitochondrial quality is essential for maintaining neuronal homeostasis, and mitochondrial transport plays a vital role in mitochondrial quality control. In this review, we first provide an overview of neuronal mitochondrial transport, followed by a detailed description of the various motors and adaptors associated with the anterograde and retrograde transport of mitochondria. Subsequently, we review the modest evidence involving mitochondrial transport mechanisms that has surfaced in acute neurological disorders, including traumatic brain injury, spinal cord injury, spontaneous intracerebral hemorrhage, and ischemic stroke. An in-depth study of this area will help deepen our understanding of the mechanisms underlying the development of various acute neurological disorders and ultimately improve therapeutic options.