Distinct CED-10/Rac1 domains confer context-specific functions in development

Abstract

Rac GTPases act as master switches to coordinate multiple interweaved signaling pathways. A major function for Rac GTPases is to control neurite development by influencing downstream effector molecules and pathways. In Caenorhabditis elegans, the Rac proteins CED-10, RAC-2 and MIG-2 act in parallel to control axon outgrowth and guidance. Here, we have identified a single glycine residue in the CED-10/Rac1 Switch 1 region that confers a non-redundant function in axon outgrowth but not guidance. Mutation of this glycine to glutamic acid (G30E) reduces GTP binding and inhibits axon outgrowth but does not affect other canonical CED-10 functions. This demonstrates previously unappreciated domain-specific functions within the CED-10 protein. Further, we reveal that when CED-10 function is diminished, the adaptor protein NAB-1 (Neurabin) and its interacting partner SYD-1 (Rho-GAP-like protein) can act as inhibitors of axon outgrowth. Together, we reveal that specific domains and residues within Rac GTPases can confer context-dependent functions during animal development.

Regulators of H3K4 methylation mutated in neurodevelopmental disorders control axon guidance in Caenorhabditis elegans

“…Caenorhabditis elegans , in which the H3K4 methylation machinery is well conserved, is an amenable model system for studying neurodevelopmental mechanisms. Factors such as a well-defined neuronal connectome and a simple body plan make this organism ideal for unveiling the roles of chromatin factors, and to assess the functional relevance of genetic variations observed in neurodevelopment diseases ( Nørgaard et al, 2018 ; Pedersen et al, 2013 ; Zallen et al, 1998 ; Boulin et al, 2006 ; Adler et al, 2006 ; Pocock and Hobert, 2008 ; Johnston and Hobert, 2003 ). In C. elegans , the process of axon guidance can be studied by following the trajectory of PVQ axons (PVQs), which run along the entire animal body in a stereotyped manner.…”

EXC-4/CLIC, Gα, and Rho/Rac signaling regulate tubulogenesis in C. elegans

“…4D). Our finding that a ced-10 mutant with reduced GTPase activity, and thus locked in the active GTP-bound form (45), enhanced the exc-4(-) outgrowth defect led us to speculate that ced-10 activity inhibits exc-4 function. However, because mutations that affect Rho/Rac GTPase activity may also compromise wildtype function , it is challenging to deduce the exact effect of ced-10/Rac activity on exc-4/CLIC function based on these genetic interactions.…”

“…The RhoG ortholog mig-2 functions in parallel to ced-10/Rac to promote ExCa outgrowth MIG-2 has primary sequence similarity to Rac1 and Cdc42, but functions in a fashion similar to RhoG (46,56). In C. elegans ced-10/Rac and mig-2/RhoG often function redundantly to regulate cell migration and outgrowth (44,45,52,53,57,58). We analyzed several mig-2 mutants (see Materials and Methods, and Supp.…”

“…Because Rho-family GTPases often function downstream of GPCR-G signaling (42), and because cell culture studies have shown that some Rho-family GTPases regulate (26), or are regulated by (21,30), CLICs, we wanted to assess the function of Rho and Rac orthologs in ExCa outgrowth (28,42). In addition, Rho-family GTPases are well-established regulators of neuronal outgrowth (43)(44)(45), and given that there are many players and mechanisms shared between ExCa and neuronal outgrowth in C. elegans, we hypothesized that Rho-family signaling may play a heretofore unrecognized role in exc-4-regulated ExCa outgrowth. The C. elegans genome encodes five canonical Rho-family GTPase orthologs: rho-1/Rho, ced-10/Rac, rac-2/Rac, cdc-42/Cdc42, and mig-2/RhoG (46).…”

“…3A, B). A second C. elegans Rac, rac-2, is redundant with ced-10 in some contexts (44,52,53), but not in others (45,54). A rac-2 deletion did not cause an ExCa phenotype on its own, nor did it exacerbate phenotypes caused by ced-10 loss (Supp.…”