Caenorhabditis elegans Inositol 5-Phosphatase Homolog Negatively Regulates Inositol 1,4,5-Triphosphate Signaling in Ovulation

Ovulation in Caenorhabditis elegans requires inositol 1,4,5-triphosphate (IP(3)) signaling activated by the epidermal growth factor (EGF)-receptor homolog LET-23. We generated a deletion mutant of a type I 5-phosphatase, ipp-5, and found a novel ovulation phenotype whereby the spermatheca hyperextends to engulf two oocytes per ovulation cycle. The temporal and spatial expression of IPP-5 is consistent with its proposed inhibition of IP(3) signaling in the adult spermatheca. ipp-5 acts downstream of let-23, and interacts with let-23–mediated IP(3) signaling pathway genes. We infer that IPP-5 negatively regulates IP(3) signaling to ensure proper spermathecal contraction.