Cloning and expression of prostaglandin E2 receptor subtype 1 (ep 1 ) in Bostrichthys sinensis

Our previous studies suggested that prostaglandin E₂ (PGE₂) is a putative sex pheromone in Chinese black sleeper Bostrichthys sinensis, a fish species that inhabits intertidal zones and mates and spawns inside a muddy burrow. We found immunoreactivities of PGE₂ receptor subtypes (Ep_1–3) expressed in the olfactory sac, but only Ep₁ presented higher density of immunoreactivity in mature fish than that in immature fish in both sexes. To gain a better understanding of the underlying molecular mechanism for the detection of PGE₂ in the olfactory system, we cloned an ep ₁ cDNA from the adult olfactory sac. The open-reading frame of the ep ₁ consisted of 1,134-bp nucleotides that encoded a 378-amino acid-long protein with a seven-transmembrane domain, typical for the G protein-coupled receptors superfamily. Expression of ep ₁ mRNA was observed in all tissues examined, with higher levels obtained in the olfactory sacs and testes. The expression of ep ₁ mRNA in the olfactory sacs and gonads was significantly higher in both sexes of mature fish than in those of immature ones. Taken together, our results suggested that Ep₁, which is highly expressed in the olfactory sacs and gonads of mature fish, is important for the control of reproduction and may be involved in PGE₂-initiated spawning behavior in B. sinensis.