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First published online 12 August 2009
doi: 10.1242/dev.039412

Development 136, 3109-3119 (2009)
Published by The Company of Biologists 2009
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Myosin II regulation during C. elegans embryonic elongation: LET-502/ROCK, MRCK-1 and PAK-1, three kinases with different roles

Christelle Gally, Frédéric Wissler, Hala Zahreddine, Sophie Quintin, Frédéric Landmann* and Michel Labouesse{dagger}

IGBMC, CNRS/ INSERM/ UdS, 1 rue Laurent Fries, BP.10142, 67400 Illkirch, France.

{dagger} Author for correspondence (lmichel{at}igbmc.fr)

Accepted 13 July 2009

Myosin II plays a central role in epithelial morphogenesis; however, its role has mainly been examined in processes involving a single cell type. Here we analyze the structure, spatial requirement and regulation of myosin II during C. elegans embryonic elongation, a process that involves distinct epidermal cells and muscles. We developed novel GFP probes to visualize the dynamics of actomyosin remodeling, and found that the assembly of myosin II filaments, but not actin microfilaments, depends on the myosin regulatory light chain (MLC-4) and essential light chain (MLC-5, which we identified herein). To determine how myosin II regulates embryonic elongation, we rescued mlc-4 mutants with various constructs and found that MLC-4 is essential in a subset of epidermal cells. We show that phosphorylation of two evolutionary conserved MLC-4 serine and threonine residues is important for myosin II activity and organization. Finally, in an RNAi screen for potential myosin regulatory light chain kinases, we found that the ROCK, PAK and MRCK homologs act redundantly. The combined loss of ROCK and PAK, or ROCK and MRCK, completely prevented embryonic elongation, but a constitutively active form of MLC-4 could only rescue a lack of MRCK. This result, together with systematic genetic epistasis tests with a myosin phosphatase mutation, suggests that ROCK and MRCK regulate MLC-4 and the myosin phosphatase. Moreover, we suggest that ROCK and PAK regulate at least one other target essential for elongation, in addition to MLC-4.

Key words: Actin, Non-muscle myosin II, Morphogenesis, Phosphorylation, Rho kinase, C. elegans


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