The small GTPase rhoA has been implicated in a variety of cellular movements. To address the role of rhoA during C. elegans development we have performed a reverse genetics approach. RNAi of the C. elegans rhoA homolog,
rho-1 , produces embryonic lethality, indicating that it is an essential gene. To identify specific requirements for
rho-1 we expressed dominant negative (dn) and gain-of-function (gf)
rho-1 under the control of the
col-10 promoter, which drives expression in hypodermal cells. Expression of this
rho-1(dn) construct causes less than the normal 12 P cells to occupy the ventral cord. Analysis of these animals suggests that P cells are missing from the ventral cord due to failed P cell migration.
unc-73 , which encodes a protein capable of acting as an exchange factor for the mammalian small GTPase, Rac1, also causes a P cell migration defect. To test whether UNC-73 acts through
rho-1 during P cell migration, we expressed
rho-1(gf) in animals homozygous for a weak
unc-73(
e936) allele. This construct was able to rescue the P cell migration defect of
unc-73 , suggesting that UNC-73 may act as an exchange factor for RHO-1, activating it during P cell migration. We have shown previously that the nuclear envelope protein UNC-84 is required for nuclear migration during P cell migration. To identify other genes that may be involved in the P cell nuclear migration, we have undertaken RNAi studies of the C. elegans homologs of NUDC and NUDF, two proteins required for Aspergillus nuclear migration. Both C. elegans genes appear to be essential, because RNAi of either can cause complete embryonic lethality in the progeny of injected animals. Although severely deformed, these embryos form a pharynx, develop gut granules and express the MH27 epitope. Interestingly, escapers from the RNAi injections are Unc, Pvl and sterile. The Unc and Pvl phenotypes are similar to those observed in animals mutant for
unc-83 or
unc-84 , which cause P cell nuclear migration defects. We are currently determining if a P cell nuclear migration defect is the cause of the Unc and Pvl phenotypes of the NUDC/F RNAi animals.