siss-1(csn20) animals are defective in stress-induced sleep (SIS) with no other obvious defects in development or behavior. csn20 is a Cys-to-Tyr substitution in the third Cys residue of the EGF motif of SISS-1 (a.k.a. IGEG-1). csn20 phenocopies the deletion allele ve532, indicating that the EGF domain of SISS-1 is functional. Reference: Hill AJ, et al. Nat Commun 15, 10886. doi: 10.1038/s41467-024-55252-4. PMID: 39738055.