RAP-1 and the RAL-1/exocyst pathway coordinate hypodermal cell organization in Caenorhabditis elegans

The small Ras‐like GTPase Rap1 has been identified as a regulator of integrin activation and cadherin‐mediated cell–cell contacts. Surprisingly, null mutants of RAP‐1 in Caenorhabditis elegans are viable and fertile. In a synthetic lethal RNAi screen with C. elegans rap‐1 mutants, the Ras‐like GTPase ral‐1 emerged as one of seven genes specifically required for viability. Depletion of exoc‐8 and sec‐5 , encoding two putative RAL‐1 effectors and members of the exocyst complex, also caused lethality of rap‐1 mutants, but did not affect wild‐type worms. The RAP‐1 and the RAL‐1/exocyst pathway appear to coordinate hypodermal cell movement and elongation during embryonic development. They mediate their effect in part through targeting the α‐catenin homologue HMP‐1 to the lateral membrane. Genetic interactions show that the RAP‐1 and RAL‐1/exocyst pathway also act in parallel during larval stages. Together these data provide in vivo evidence for the exocyst complex as a downstream RAL‐1 effector in cell migration.