Luxton, G. W. G. | bioRxiv Science

bioRxiv2024

Anchorage of H3K9-methylated heterochromatin to the nuclear periphery helps mediate P-cell nuclear migration though constricted spaces in Caenorhabditis elegans

Nuclei adjust their deformability while migrating through constrictions to enable structural changes and maintain nuclear integrity. The effect of heterochromatin anchored at the nucleoplasmic face of the inner nuclear membrane on nuclear morphology and deformability during in vivo nuclear migration through constricted spaces remains unclear. Here, we show that abolishing peripheral heterochromatin anchorage by eliminating CEC-4, a chromodomain protein that tethers H3K9-methylated chromatin to the nuclear periphery, disrupts constrained P-cell nuclear migration in Caenorhabditis elegans larvae in the absence of the established LINC complex-dependent pathway. CEC-4 acts in parallel to an actin and CDC-42-based pathway. We also demonstrate the necessity for the chromatin methyltransferases MET-2 and JMJD-1.2 during P-cell nuclear migration in the absence of functional LINC complexes. We conclude that H3K9-nethylated chromatin needs to be anchored to the nucleoplasmic face of the inner nuclear membrane to help facilitate nuclear migration through constricted spaces in vivo.

genetics↗

bioRxiv2021

The luminal AAA+ ATPase torsinA mediates distinct mechanisms of nuclear-cytoplasmic communication by adopting different functional assembly states.

Chemical and mechanical nuclear-cytoplasmic communication across the nuclear envelope (NE) is largely mediated by the nuclear pore complex (NPC) and the linker of nucleoskeleton and cytoskeleton (LINC) complex, respectively. While NPC and LINC complex assembly are functionally related, the mechanisms responsible for this relationship remain poorly understood. Here, we investigated how the luminal ATPases associated with various cellular activities (AAA+) protein torsinA promotes NPC and LINC complex assembly using fluorescence fluctuation spectroscopy (FFS), quantitative photobleaching analyses, and functional cellular assays. We report that torsinA controls LINC complex-dependent nuclear-cytoskeletal coupling as a soluble hexameric AAA+ protein and interphase NPC biogenesis as a membrane-associated helical polymer. These findings help resolve the conflicting models of torsinA function that were recently proposed based on in vitro structural studies. Our results will enable future studies of the role of defective nuclear-cytoplasmic communication in DYT1 dystonia and other diseases caused by mutations in torsinA.

cell biology↗

bioRxiv2018

Imbalanced Nucleocytoskeletal Connections Create Common Polarity Defects in Progeria and Physiological Aging

Studies of the accelerated aging disorder Hutchinson-Gilford progeria syndrome (HGPS) can potentially reveal cellular defects associated with physiological aging. HGPS results from expression and abnormal nuclear envelope association of a farnesylated, truncated variant of prelamin A called progerin. We surveyed the diffusional mobilities of nuclear membrane proteins to identify proximal effects of progerin expression. The mobilities of three proteins were reduced in fibroblasts from children with HGPS compared to normal fibroblasts: SUN2, nesprin-2G, and emerin. These proteins function together in nuclear movement and centrosome orientation in fibroblasts polarizing for migration. Both processes were impaired in fibroblasts from children with HGPS and in NIH3T3 fibroblasts expressing progerin, but were restored by inhibiting protein farnesylation. Progerin affected both the coupling of the nucleus to actin cables and the oriented flow of the cables necessary for nuclear movement and centrosome orientation. Progerin overexpression increased levels of SUN1, which couples the nucleus to microtubules through nesprin-2G and dynein, and microtubule association with the nucleus. Reducing microtubule-nuclear connections through SUN1 depletion or dynein inhibition rescued the polarity defects. Nuclear movement and centrosome orientation were also defective in fibroblasts from normal individuals over 60 years old and both defects were rescued by reducing the increased level of SUN1 in these cells or inhibiting dynein. Our results identify imbalanced nuclear engagement of the cytoskeleton (microtubules, high; actin filaments, low) as the basis for intrinsic cell polarity defects in HGPS and physiological aging and suggest that rebalancing the connections can ameliorate the defects.\n\nSignificanceThe rare, premature aging syndrome HGPS arises from expression of a pathological prelamin A variant, termed progerin. Studies of progerin may identify treatments for HGPS and reveal novel cellular and molecular characteristics of normal aging. Here, we show that progerin selectively affects mobilities of three nuclear membrane proteins, SUN2, nesprin-2G and emerin that position the nucleus and establish cell polarity essential for migration. We find that both processes are defective in fibroblasts from children with HGPS and aged (> 60 years) individuals. The mechanism underlying these defects is excessive interaction of the nucleus with microtubules. Our work identifies nuclear-based defects in cell polarization as intrinsic factors in premature and physiological aging and suggests means for correcting them.

cell biology↗