Presentation/Session Information

Session Information

Session Title: Cell Fate, Differentiation and Morphogenesis Session Type: Parallel
Session Location: Northwest Auditorium Session Time: Sat, Jun 27 8:30AM - 11:30AM

Presentation Information

Program Number: 184 Presentation Time: 10:18AM - 10:30AM

Presentation Content

LET-502/ ROCK acting independently of myosin-II promotes junctional protein transport or trafficking in parallel to microtubules.Sophie Quintin 1, Christelle Gally 1, Shaohe Wang 2, Karen Oegema 2, Michel Labouesse 1. 1)IGBMC/ CERBM, 1 rue Laurent Fries, BP 10142, 67404 Illkirch, France; 2)Ludwig Institute for Cancer Research, Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla CA 92037

During C. elegans morphogenesis, the embryo elongates through epidermal cell shape changes. Two processes are required for elongation: actomyosin contractility controlled by LET-502/ROCK activity, and muscle contractions, which trigger a mechanotransduction pathway in the epidermis through hemidesmosomes (HDs). In addition, microtubules (MTs) play a poorly understood role (Priess and Hirsh, 1986). To define how MTs contribute to elongation, we first examined their organization and dynamics in elongating embryos. We find that two minus-end MT regulators, γ-tubulin and NOCA-1, localize to adherens junctions and along HDs. To disrupt MTs, we specifically expressed the MT-severing protein SPASTIN in the epidermis. This does not strongly affect morphogenesis, unless LET-502/ROCK activity or HDs are partially compromised. Cellular and kinetic data suggest that MTs mainly act by promoting the transport of E-cadherin to adherens junctions and myotactin/LET-805 to HDs, which are critical for elongation. Importantly, let-502/ROCK activity potentiates MT transport, independently of myosin-dependent tension. To look for genes involved in MT-mediated transport and elongation, we performed two independent RNAi screens. The first screen targeted genes whose depletion phenocopied the hypo-elongated phenotype of spastin expression in let-502(lf) animals. Tubulin folding and centrosome biogenesis genes were identified, confirming that MT levels are critical when let-502 is lowered. Among traffic candidate genes, the syntaxin SYX-5 stood out as a key player acting with LET-502. Our data suggest that syx-5 could act by promoting vesicle fusion events close to adherens junctions or HDs. In the second screen, we looked for genes acting in parallel to git-1, the earliest acting factor in the mechanotransduction pathway. We identified genes of the minus-end directed MT motor dynein/dynactin, including a novel component of the complex, FARL-11. Several members of the dynein complex, including farl-11 and dlc-1, were found to localize along HDs. Interestingly, dlc-1 localization pattern depends on a critical serine residue, which needs to be unphosphorylated. Altogether, our data suggest that HDs act as a platform where MTs could be nucleated and trapped, to allow the delivery of proteins essential for elongation. Our finding that LET-502/ROCK reinforces this process independently of its role as a myosin II activator implies that it acts through a target controlling trafficking.




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