A Nesprin-4/kinesin-1 cargo model for nuclear positioning in cochlear outer hair cells

The KASH protein UNC-83 differentially regulates kinesin-1 activity to control developmental stage-specific nuclear migration

Nuclear migration plays a fundamental role in development, requiring precise spatiotemporal control of bidirectional movement through dynein and kinesin motors. Here, we uncover a mechanism for developmental regulation of nuclear migration directionality. The nuclear envelope KASH protein UNC-83 in Caenorhabditis elegans exists in multiple isoforms that differentially control motor activity. The shorter UNC-83c isoform promotes kinesin-1-dependent nuclear movement in embryonic hyp7 precursors, while longer UNC-83a/b isoforms facilitate dynein-mediated nuclear migration in larval P cells. We demonstrate that UNC-83a's N-terminal domain functions as a kinesin-1 inhibitory module by directly binding kinesin heavy chain (UNC-116). This isoform-specific inhibition, combined with differential affinity for kinesin light chain (KLC-2), establishes a molecular switch for directional control. Together, these interdisciplinary studies reveal how alternative isoforms of cargo adaptors can generate developmental stage-specific regulation of motor activity during development.

Active microtubule-actin cross-talk mediated by a nesprin-2G-kinesin complex

Nesprin-2 Giant (N2G) is a large integral membrane protein that physically connects the nucleus to the cytoskeleton, but how N2G performs this activity to maintain nuclear positioning and drive nuclear movement is unclear. This study investigates N2G's role in nucleocytoskeletal coupling, a process critical for cellular function and development. We uncover multiple roles for N2G, including its activity as an F-actin bundler, an adapter that activates kinesin-1 motors, and a mediator of cytoskeletal cross-talk. Notably, N2G directly links kinesin-1 to F-actin, enabling the transport of actin filaments along microtubule tracks, establishing active cross-talk between the actin and microtubule cytoskeletons. These findings provide crucial insights into nuclear movement, advancing our understanding of fundamental cellular processes and their implications in development and disease.

The LINC complex in blood vessels: from physiology to pathological implications in arterioles

The LINC (linker of nucleoskeleton and cytoskeleton) complex is a critical component of the cellular architecture that bridges the nucleoskeleton and cytoskeleton and mediates mechanotransduction to and from the nucleus. Though it plays important roles in all blood vessels, it is in arterioles that this complex plays a pivotal role in maintaining endothelial cell integrity, regulating vascular tone, forming new microvessels and modulating responses to mechanical and biochemical stimuli. It is also important in vascular smooth muscle cells and fibroblasts, where it possibly plays a role in the contractile to secretory phenotypic transformation during atherosclerosis and vascular ageing, and in fibroblasts' migration and inflammatory responses in the adventitia. Physiologically, the LINC complex contributes to the stability of arteriolar structure, adaptations to changes in blood flow and injury repair mechanisms. Pathologically, dysregulation or mutations in LINC complex components can lead to compromised endothelial function, vascular remodelling and exacerbation of cardiovascular diseases such as atherosclerosis (arteriolosclerosis). This review summarizes our current understanding of the roles of the LINC complex in cells from arterioles, highlighting its most important physiological functions, exploring its implications for vascular pathology and emphasizing some of its functional characteristics in endothelial cells. By elucidating the LINC complex's role in health and disease, we aim to provide insights that could improve future therapeutic strategies targeting LINC complex-related vascular disorders.

Unraveling the nexus of nesprin in dilated cardiomyopathy: From molecular insights to therapeutic prospects

Dilated cardiomyopathy is a complex and debilitating heart disorder characterized by the enlargement and weakening of the cardiac chambers, leading to impaired contractility and heart failure. Nesprins, a family of nuclear envelope spectrin repeat proteins that include isoforms Nesprin-1/-2, are integral components of the LInker of Nucleoskeleton and Cytoskeleton complex. They facilitate the connection between the nuclear envelope and the cytoskeleton, crucial for maintaining nuclear architecture, migration and positioning, and mechanical transduction and signaling. Nesprin-1/-2 are abundantly expressed in cardiac and skeletal muscles.They have emerged as key players in the pathogenesis of dilated cardiomyopathy. Mutations in synaptic nuclear envelope-1/-2 genes encoding Nesprin-1/-2 are associated with dilated cardiomyopathy, underscoring their significance in cardiac health. This review highlights the all known cases of Nesprin-1/-2 related dilated cardiomyopathy, focusing on their interactions with the nuclear envelope, their role in mechanical transduction, and their influence on gene expression. Moreover, it delves into the underlying mechanisms through which Nesprin dysfunction disrupts nuclear-cytoskeletal coupling, leading to abnormal nuclear morphology, impaired mechanotransduction, and altered gene regulation. The exploration of Nesprin's impact on dilated cardiomyopathy offers a promising avenue for therapeutic interventions aimed at ameliorating the disease. This review provides a comprehensive overview of recent advancements in understanding the pivotal role of Nesprins in dilated cardiomyopathy research.

Nesprin-2 coordinates opposing microtubule motors during nuclear migration in neurons

Nuclear migration is critical for the proper positioning of neurons in the developing brain. It is known that bidirectional microtubule motors are required for nuclear transport, yet the mechanism of the coordination of opposing motors is still under debate. Using mouse cerebellar granule cells, we demonstrate that Nesprin-2 serves as a nucleus-motor adaptor, coordinating the interplay of kinesin-1 and dynein. Nesprin-2 recruits dynein-dynactin-BicD2 independently of the nearby kinesin-binding LEWD motif. Both motor binding sites are required to rescue nuclear migration defects caused by the loss of function of Nesprin-2. In an intracellular cargo transport assay, the Nesprin-2 fragment encompassing the motor binding sites generates persistent movements toward both microtubule minus and plus ends. Nesprin-2 drives bidirectional cargo movements over a prolonged period along perinuclear microtubules, which advance during the migration of neurons. We propose that Nesprin-2 keeps the nucleus mobile by coordinating opposing motors, enabling continuous nuclear transport along advancing microtubules in migrating cells.

Diverse Roles of the LINC Complex in Cellular Function and Disease in the Nervous System

The linker of nucleoskeleton and cytoskeleton (LINC) complex, which spans the nuclear envelope, physically connects nuclear components to the cytoskeleton and plays a pivotal role in various cellular processes, including nuclear positioning, cell migration, and chromosomal configuration. Studies have revealed that the LINC complex is essential for different aspects of the nervous system, particularly during development. The significance of the LINC complex in neural lineage cells is further corroborated by the fact that mutations in genes associated with the LINC complex have been implicated in several neurological diseases, including neurodegenerative and psychiatric disorders. In this review, we aimed to summarize the expanding knowledge of LINC complex-related neuronal functions and associated neurological diseases.

Nesprin proteins: bridging nuclear envelope dynamics to muscular dysfunction

This review presents a comprehensive exploration of the pivotal role played by the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex, with a particular focus on Nesprin proteins, in cellular mechanics and the pathogenesis of muscular diseases. Distinguishing itself from prior works, the analysis delves deeply into the intricate interplay of the LINC complex, emphasizing its indispensable contribution to maintaining cellular structural integrity, especially in mechanically sensitive tissues such as cardiac and striated muscles. Additionally, the significant association between mutations in Nesprin proteins and the onset of Dilated Cardiomyopathy (DCM) and Emery-Dreifuss Muscular Dystrophy (EDMD) is highlighted, underscoring their pivotal role in disease pathogenesis. Through a comprehensive examination of DCM and EDMD cases, the review elucidates the disruptions in the LINC complex, nuclear morphology alterations, and muscular developmental disorders, thus emphasizing the essential function of an intact LINC complex in preserving muscle physiological functions. Moreover, the review provides novel insights into the implications of Nesprin mutations for cellular dynamics in the pathogenesis of muscular diseases, particularly in maintaining cardiac structural and functional integrity. Furthermore, advanced therapeutic strategies, including rectifying Nesprin gene mutations, controlling Nesprin protein expression, enhancing LINC complex functionality, and augmenting cardiac muscle cell function are proposed. By shedding light on the intricate molecular mechanisms underlying nuclear-cytoskeletal interactions, the review lays the groundwork for future research and therapeutic interventions aimed at addressing genetic muscle disorders.

A humanized Caenorhabditis elegans model of hereditary spastic paraplegia-associated variants in KLC4

Hereditary spastic paraplegia (HSP) is a group of degenerative neurological disorders. We identified a variant in human kinesin light chain 4 (KLC4) that is suspected to be associated with autosomal-dominant HSP. How this and other variants relate to pathologies is unknown. We created a humanized Caenorhabditis elegans model in which klc-2 was replaced by human KLC4 (referred to as hKLC4) and assessed the extent to which hKLC4 retained function in the worm. We observed a slight decrease in motility but no nuclear migration defects in the humanized worms, suggesting that hKLC4 retains much of the function of klc-2. Five hKLC4 variants were introduced into the humanized model. The clinical variant led to early lethality, with significant defects in nuclear migration when homozygous and a weak nuclear migration defect when heterozygous, possibly correlating with the clinical finding of late-onset HSP when the proband was heterozygous. Thus, we were able to establish humanized C. elegans as an animal model for HSP and to use it to test the significance of five variants of uncertain significance in the human gene KLC4.