The giant nesprin-1/2 ortholog ANC-1 anchors organelles through regulating macromolecular crowding

Speaker: GW Gant Luxton, University of California-Davis

Host: Arpita Upadhyaya

Abstract: Macromolecular crowding considerably influences biochemical reaction rates and the physical properties of intracellular environments. Recent advances have made progress on how crowding is modulated in individual cultured cells by regulating ribosome concentrations. However, the mechanisms that regulate molecular crowding throughout development in multicellular in vivo contexts are largely unexplored. Here, we used genetically encoded multimeric nanoparticles (GEMs) to study the physical properties of the cell interior within developing tissues of the multicellular organism, C. elegans. GEMs are homomultimeric scaffolds fused to a green fluorescent protein that self-assemble into bright, stable particles 40 nm in diameter. To use GEMs to perform single-particle tracking nanorheology experiments in vivo, we engineered C. elegans strains stably expressing 40 nm GEMs under the control of tissue-specific promoters in the hypodermis, intestine, and neurons. GEMs exhibited tissue-specific effective diffusion coefficients. We observed more immobile GEMs in the hypodermis and intestine than we observed in neurons or previously reported in individual yeast, or mammalian tissue culture cells. Previous nanorheology studies performed in cultured mammalian cells identified the conserved nuclear envelope-spanning linker of nucleoskeleton and cytoskeleton (LINC) complex as a key determinant of cellular mechanical stiffness. Interestingly, we recently demonstrated that the nesprin-1/2 ortholog ANC-1 controls the intracellular positioning of the endoplasmic reticulum, nuclei, lipid droplets, and mitochondria through a LINC complex-independent mechanism. Therefore, we hypothesized that ANC-1 anchors organelles through regulating macromolecular crowding. We found that the effective GEM diffusion coefficients were considerably increased in C. elegans intestinal or hypodermal cells lacking ANC-1. In contrast, no significant effect on GEM mobility was observed in strains null for the SUN protein UNC-84, or harboring muscular dystrophy-associated mutations in the nuclear lamin protein, LMN-1. Furthermore, we demonstrate that ANC-1 is required for the homogeneous cytoplasmic distribution of ribosomes in vivo. Collectively, these results establish a LINC complex-independent role for ANC-1 in controlling the mesoscale biophysical properties of the cytoplasm in vivo across several different tissues.  

Seminars start at 4:00 pm, and refreshments will be served at 3:45 pm. All seminars are held in the Conference Room (1116) of the Institute for Physical Science and Technology (IPST) Building unless otherwise noted.