Myosin II regulation during C. elegans embryonic elongation: LET-502/ROCK, MRCK-1 and PAK-1, three kinases with different roles.
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.
Gally
Christelle
C
IGBMC, CNRS/ INSERM/ UdS, 1 rue Laurent Fries, BP.10142, 67400 Illkirch, France.
Wissler
Frédéric
F
Zahreddine
Hala
H
Quintin
Sophie
S
Landmann
Frédéric
F
Labouesse
Michel
M
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000033:anatomy & histology / Q000196:embryology / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000502:physiology*; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism; D024462:Myosin Type II / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D019076:Transgenes; D054462:p21-Activated Kinases / Q000235:genetics / Q000378:metabolism*; D054460:rho-Associated Kinases / Q000235:genetics / Q000378:metabolism*
D029742:Caenorhabditis elegans Proteins; D018994:Myosin Light Chains; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C101878:pak-1 protein, C elegans; C515856:LET-502 protein, C elegans; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D054460:rho-Associated Kinases; D024462:Myosin Type II