Ovulation in C. elegans is dependent on inositol (1,4,5) triphosphate (IP 3 ) signaling. Here, we report the genetic characterization of a Type I inositol polyphosphate 5-phosphatase (5-Ptase) and its function in ovulation. The Caenorhabditis elegans Type I 5-Ptase gene,
ipp-5 , is expressed in the spermetheca, pharynx, and vulva. The ipp- 5 deletion mutant,
sy605 , shows a novel ovulation phenotype whereby the spermetheca extends further to ovulate two oocytes during a single ovulation cycle; thus indicating that IPP-5 helps to regulate spermethecal contractile behavior during ovulation and is necessary to prevent hyper- extension of the spermetheca. This defect is opposite to the result of decreased EGFR function in which the spermetheca fails to dilate. Genetic analysis indicates
ipp-5 acts downstream of
let-23.
ipp-5 suppresses the sterile defect of
lin-3(rf) and
let-23(rf). ipp- 5 interacts with others genes in the
let-23 -mediated IP3 signaling pathway: it synergizes with
let-23(gf),
lfe-1/itr-1/dec-4 , and
lfe-2 . Our data support the hypothesis that increased IP3 signaling causes increased extension of the spermetheca during ovulation and that either too much signaling or too little signaling prevents ovulation. We propose that IP3 signaling levels modulate spermetheca contractions and dilations during ovulation possibly through regulating calcium release. The expression of IPP-1 is consistent with its function in ovulation in the adult spermetheca.