The RhoGAP HUM-7/Myo9 integrates signals to modulate RHO-1/RhoA during embryonic morphogenesis in Caenorhabditis elegans

Abstract

During embryonic morphogenesis, cells and tissues undergo dramatic movements under the control of F-actin regulators. Our studies of epidermal cell migrations in developing Caenorhabditis elegans embryos have identified multiple plasma membrane signals that regulate the Rac GTPase, thus regulating WAVE and Arp2/3 complexes, to promote branched F-actin formation and polarized enrichment. Here, we describe a pathway that acts in parallel to Rac to transduce membrane signals to control epidermal F-actin through the GTPase RHO-1/RhoA. RHO-1 contributes to epidermal migration through effects on underlying neuroblasts. We identify signals to regulate RHO-1-dependent events in the epidermis. HUM-7, the C. elegans homolog of human MYO9A and MYO9B, regulates F-actin dynamics during epidermal migration. Genetics and biochemistry support that HUM-7 behaves as a GTPase-activating protein (GAP) for the RHO-1/RhoA and CDC-42 GTPases. Loss of HUM-7 enhances RHO-1-dependent epidermal cell behaviors. We identify SAX-3/ROBO as an upstream signal that contributes to attenuated RHO-1 activation through its regulation of HUM-7/Myo9. These studies identify a new role for RHO-1 during epidermal cell migration, and suggest that RHO-1 activity is regulated by SAX-3/ROBO acting on the RhoGAP HUM-7.

SLIT2/ROBO1-signaling inhibits macropinocytosis by opposing cortical cytoskeletal remodeling

“…However, the mechanism of SLIT3-induced RhoA activation remains to be elucidated. Our findings are consistent with recent work demonstrating that exposure to NSlit2 causes inactivation of MYO9B in human lung carcinoma cells 39 , and inactivation of the MYO9B ortholog in Caenorhabditis elegans 80 . The present study's findings are in contrast to our previous observation that, in rat fibroblasts, NSlit2 inhibited transforming growth factor-βinduced actin stress fiber formation, possibly by inhibiting RhoA 70 .…”

Game of Tissues: How the Epidermis Thrones C. elegans Shape

“…Loss of any of these mediators results in an overall reduction of protrusive activity of the "leading cells" which either halt or slow down ventral migration causing ventral enclosure defects ( Figure 2C inset) [24,[29][30][31][32][33][34]. On the other hand, in the "pocket cells", the axis ECT-2(RHOA GEF)-RHO-1-LET-502(ROCK) restricts protrusive ability while enhancing the actin motor non-muscle myosin II (NMY-2) contractility to ensure constriction of the actin ring, enclosing the ventral pocket ( Figure 2D inset) [31,[33][34][35]. Once the epidermal cells meet, new CeAJs must form.…”

“…hand, in the "pocket cells", the axis ECT-2(RHOA GEF)-RHO-1-LET-502(ROCK) restricts protrusive ability while enhancing the actin motor non-muscle myosin II (NMY-2) contractility to ensure constriction of the actin ring, enclosing the ventral pocket ( Figure 2D inset) [31,[33][34][35]. Once the epidermal cells meet, new CeAJs must form.…”

Multi-tissue patterning drives anterior morphogenesis of theC. elegansembryo

“…It is not clear how the neuroblasts could affect epidermal cell migration. As described earlier, signaling pathways that regulate WSP-1 and WVE-1 to control the formation of branched F-actin have been implicated in ventral epidermal cell migration during ventral enclosure, and it is likely that they could influence their anterior migration as well (Sawa et al, 2003;Withee et al, 2004;Patel et al, 2008;Bernadskaya et al, 2012;Wallace et al, 2018). It is not clear where the ligands for these pathways are located (e.g., Bernadskaya et al, 2012), but we favor the hypothesis that they originate from the subset of neuroblasts that form the pentagon and/or semi-circle around the BFP.…”

“…Other signaling pathways implicated in controlling ventral epidermal cell migration include semaphorin and plexin (PLX-2; Roy et al, 2000;Nakao et al, 2007;Ikegami et al, 2012). One model is that the receptors are expressed in the epidermal cells and receive cues from the neuroblasts or neighbouring epidermal cells to regulate branched F-actin assembly for their migration (Withee et al, 2004;Chisholm and Hardin, 2005;Patel et al, 2008;Patel and Soto, 2013;Wallace et al, 2018). In addition, subsets of neuroblasts in the middle-posterior of the embryo form rosettes, likely via planar cell polarity, to elongate the tissue in preparation for epidermal elongation.…”