Ras-RalGEF-Ral-dependent developmental events in C. elegans development and metabolism
Ras is the most mutated oncoprotein, with ~30% of tumors driven by activated Ras. Among three Ras effectors of roughly equivalent oncogenicity, Ras-Raf and Ras-PI3K are well studied, but the downstream mechanisms of Ras-RalGEF-Ral signaling remain poorly understood. Ral (Ras-like) is a small GTPase related to Ras. The fundamental gap in our understanding of Ras-RalGEF-Ral signaling is because Ral is both a component of the heterooctomeric exocyst complex and uses the exocyst as a signaling intermediary, which precludes conventional biochemical bootstrapping to identify signal transduction components downstream of the exocyst. Consequently, we are using genetic analysis of Ral signaling in C. elegans to identify roles of Ral in development and metabolism, and to use roles to investigate activities downstream of Ral. In addition to its previously published function in vulval cell fate patterning, we found that Ral may function in six different contexts. 1) Constitutively activated endogenous Ral (RAL-1(gf)) causes a defect in lipid synthesis and/or storage in the intestine. 2) Redundant Ral and Rap1 (Ras Proximal) are required for progression through embryonic morphogenesis, possibly through regulation of the exocyst. 3) Ral effector Rlbp1 (a GAP for Cdc42/Rac) rand mir-61 may repress an anti-2˚ signal in the in vulval cell fate patterning. 4) Constitutively activated Ras functions in parallel to DAF-2/InsR, not through Ras-Raf but likely Ras-PI3K or Ras-RalGEF-Ral. 5) Ras-RalGEF-Ral contributes to CAN cell migration and other events during sculpting of the nervous system. 6) RAL-1(gf) in combination with deletion of GCK-2 causes phenotypes consistent with defective development of the utse cell and the ventral uterus. Taken together, our results highlight multiple roles of Ral signaling in development, and positions us for mutant screens to identify downstream components of Ral signaling in different contexts.