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

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Abstract
Ovulation in Caenorhabditis elegans requires inositol 1,4,5-triphosphate (IP3) 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 IP3 signaling in the adult spermatheca. ipp-5 acts downstream oflet-23, and interacts withlet-23–mediated IP3 signaling pathway genes. We infer that IPP-5 negatively regulates IP3signaling to ensure proper spermathecal contraction.