New evidence for the involvement of prostaglandin receptor EP4b in ovulation of the medaka, Oryzias latipes

A cDNA for a prostaglandin E2 (PGE2) receptor subtype 4, EP4b (Ptger4b), was cloned from the medaka ovary. The effect of PGE2 was examined using COS-7 cells expressing the recombinant Ptger4b protein. An increase in intracellular cAMP levels was observed when the cells were incubated with PGE2, but the increase in cAMP levels was nullified by the addition of the EP4 antagonist GW627368X. The expression of ptger4b mRNA was drastically induced by the addition of pregnant mare serum gonadotropin to the in vitro culture of large preovulatory follicles. In in vitro ovulation studies of the effect of GW627368X addition on follicle ovulation, the critical timing of the PGE2/Ptger4b interaction was suggested to be between −1 and 0 h of ovulation. These results further substantiate that PGE2/Ptger4b signaling is involved in follicle rupture during ovulation in the medaka ovary.

► Isolation of a cDNA for EP4b, a PGE2 receptor, from the teleost medaka ovary.
► Demonstration of binding of PGE2 (agonist) and GW627368X (antagonist) to EP4b using COS-7 cells.
► In vitro PMSG induction of EP4b mRNA in the preovulatory follicles that are destined to ovulate.
► Evidence for the importance of PGE2 binding to the receptor at or around the time of ovulation for successful ovulation.