UNC-73/Trio RhoGEF-2 Activity Modulates Caenorhabditis elegans Motility Through Changes in Neurotransmitter Signaling Upstream of the GSA-1/Gαs Pathway

Abstract

Rho-family GTPases play regulatory roles in many fundamental cellular processes. Caenorhabditis elegans UNC-73 RhoGEF isoforms function in axon guidance, cell migration, muscle arm extension, phagocytosis, and neurotransmission by activating either Rac or Rho GTPase subfamilies. Multiple differentially expressed UNC-73 isoforms contain a Rac-specific RhoGEF-1 domain, a Rho-specific RhoGEF-2 domain, or both domains. The UNC-73E RhoGEF-2 isoform is activated by the G-protein subunit Ga q and is required for normal rates of locomotion; however, mechanisms of UNC-73 and Rho pathway regulation of locomotion are not clear. To better define UNC-73 function in the regulation of motility we used cell-specific and inducible promoters to examine the temporal and spatial requirements of UNC-73 RhoGEF-2 isoform function in mutant rescue experiments. We found that UNC-73E acts within peptidergic neurons of mature animals to regulate locomotion rate. Although unc-73 RhoGEF-2 mutants have grossly normal synaptic morphology and weak resistance to the acetylcholinesterase inhibitor aldicarb, they are significantly hypersensitive to the acetylcholine receptor agonist levamisole, indicating alterations in acetylcholine neurotransmitter signaling. Consistent with peptidergic neuron function, unc-73 RhoGEF-2 mutants exhibit a decreased level of neuropeptide release from motor neuron dense core vesicles (DCVs). The unc-73 locomotory phenotype is similar to those of rab-2 and unc-31, genes with distinct roles in the DCV-mediated secretory pathway. We observed that constitutively active Ga s pathway mutations, which compensate for DCV-mediated signaling defects, rescue unc-73 RhoGEF-2 and rab-2 lethargic movement phenotypes. Together, these data suggest UNC-73 RhoGEF-2 isoforms are required for proper neurotransmitter signaling and may function in the DCV-mediated neuromodulatory regulation of locomotion rate.

Locomotion Behavior Is Affected by the GαS Pathway and the Two-Pore-Domain K+ Channel TWK-7 Interacting in GABAergic Motor Neurons in Caenorhabditis elegans

“…Hence, we next tested the corresponding upstream G protein GSA-1 and the phosphodiesterase PDE-4, a negative regulator of Ga S signaling, for their effects on locomotor activity. Consistent with previous reports (Charlie et al 2006;Hu et al 2011), the two Ga S (gf) mutant alleles gsa-1(ce94) and pde-4(ce268) also showed enhanced swimming and spontaneous crawling activity similar to that of kin-2(cau1) and kin-2(ce179) (Figure 1, A-C).…”

GEFs and Rac GTPases control directional specificity of neurite extension along the anterior–posterior axis

“…In contrast, a different isoform, UNC-73E, which contains only the RhoGEF domain, activates Rho GTPases and regulates both cell migration and locomotion (26,27). We found that missense mutations u908 and rh40 and splice donor mutation e936, which all alter UNC-73B, resulted in shortened ANs from both the PLM and ALM.…”

Systematic profiling of C aenorhabditis elegans locomotive behaviors reveals additional components in G-protein Gαq signaling

“…Therefore, we cannot pinpoint the PLC-3 site of action. It was reported that UNC-73 has EGL-30-independent functions regulating locomotive behaviors in neurons other than motor neurons (17). It would be interesting to find whether PLC-3 also functions in those cells.…”

“…A later study argued that the Rho GEF domain of UNC-73/Trio (referred to as UNC-73 hereafter) was the other EGL-30/Gαq target (15). It was suggested that UNC-73 functions in parallel or downstream of the DAG kinase DGK-1 and inhibits the conversion of DAG to phosphatidic acid (16,17). Although this explains how UNC-73 stabilizes DAG once it is produced, it remains unclear how UNC-73 regulates the production of DAG.…”