The conserved Ras signaling pathway regulates multiple cell fates during Caenorhabditis elegans development. Genetic analyses suggest that a major function of this pathway during vulval development is to negatively regulate
lin-1 which encodes an ETS-domain containing protein. ETS-domain transcription factors typically function as transcription factors and are conserved mediators of Ras signaling. Many genes have been identified that act upstream of
lin-1, however little is known about the molecules acting downstream of
lin-1 that function as effectors of appropriate cell fates in response to the Ras-mediated signal. To identify genes that interact with
lin-1, we screened for suppressors of the multivulval (Muv) phenotype caused by
lin-1(
n383); a non-null but nonetheless strong loss-of-function allele. One suppressor mutation caused fully penetrant rod-like lethality. The same phenotype is caused by mutations that completely inactivate the Ras pathway, indicating that the gene identified by this mutation may play a crucial role in Ras signaling during early development. Animals that are heterozygous for this mutation display partial suppression of the Muv phenotypes caused by
let-60(
n1046), an activating mutation in the C. elegans Ras gene, and
lin-1(
e1275), a weak loss-of-function allele. This mutation was mapped using genetic and polymorphic markers to a small region in the middle of chromosome I. Transformation rescue experiments have identified a minimal construct that contains only one predicted open reading frame and is sufficient for rescue of the lethal phenotype; this transgene also conveys a partially penetrant Muv phenotype. This open reading frame encodes the C. elegans homologue of the Ras-like molecule, Rab8. We have not yet identified the molecular lesion associated with the mutation, however,
rab-8 dsRNA suppresses the
let-60(
n1046) multivulval phenotype when introduced via feeding experiments. Rab proteins are small GTPases that regulate vesicular transport during exocytosis and endocytosis, and Rab8 proteins are implicated in transport between the trans-Golgi network and the plasma membrane. Rab8 and its interacting proteins appear to play a conserved role in modulating cellular morphology in response to developmental signals. Rab8 proteins have not been previously implicated in the regulation of Ras signaling or vulval development.