IGEG-2 is a C. elegans EGFR ligand

Across species, Epidermal Growth Factor (EGF) family ligands and their receptors participate in developmental and physiological cell-cell signaling events. C. elegans possesses a single EGF receptor, LET-23 /EGFR, and two characterized EGF ligands. LIN-3 /EGF is well-known for its role in vulval induction, and SISS-1 /EGF mediates stress-induced sleep. The C. elegans genome harbors another predicted EGF family member, igeg-2 , which has not been characterized. To determine if IGEG-2 is a functional EGFR ligand, we examined whether it can activate known LET-23-dependent processes. We found that ubiquitous overexpression of IGEG- 2 promotes both vulval induction and sleep, indicating that it is a functional EGF family ligand. The endogenous role of IGEG-2 remains unknown.