Sahabandu, N. | Search bioRxiv

bioRxiv2025

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-83as 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.

cell biology↗

bioRxiv2024

Active Microtubule-Actin Crosstalk Mediated by a Nesprin-2G-Kinesin Complex

Nesprins are integral membrane proteins that physically couple the nucleus and cytoskeleton. Nesprin-2 Giant (N2G) stands out for its extensive cytoplasmic domain, which contains tandem N-terminal actin-binding calponin-homology domains followed by >50 spectrin repeats and a C-terminal outer nuclear membrane-spanning KASH domain. N2Gs KASH domain interacts with the inner nuclear membrane, lamina-binding SUN proteins within the perinuclear space, forming a linker of nucleoskeleton and cytoskeleton (LINC) complex. Additionally, N2G contains a conserved W-acidic LEWD motif that enables the direct interaction with kinesin-1s light chain, indicating N2Gs involvement with both actin and microtubules. The absence of N2G leads to embryonic lethality in mice, while cellular assays highlight N2Gs role in nuclear positioning across diverse biological contexts. However, the precise mechanisms underlying N2G-mediated nucleocytoskeletal coupling remain unclear. Here we study N2Gs interactions with F-actin and kinesin-1, revealing its functions as an F-actin bundler, a kinesin-1-activating adapter, and a mediator of active cytoskeletal crosstalk. Along with MAP7 proteins, N2G directly links active kinesin-1 motors to F-actin, facilitating actin transport along microtubule tracks. These findings shed light on N2Gs dynamic role as a crosslinker between actin and microtubule cytoskeletons, offering insights into nuclear movement, a fundamental cellular process.

biophysics↗