Testis

Quantification of Prolactin (PRL) and PRL Receptor Messenger RNA in Gilthead Seabream (Sparus aurata) after Treatment with Estradiol-17ß

Abstract

Prolactin (PRL) in fish is considered to be an osmoregulatory hormone, although some studies suggest that it may influence the production of steroid hormones in the gonads. The objective of the present study was to establish if PRL is involved in the reproduction of the gilthead seabream - a protandrous hermaphrodite. Adult and juvenile gilthead seabream received implants of estradiol-17ß (E₂) for one week during the breeding season and the mRNA expression of PRL and PRL receptor (sbPRLR) was determined. Northern blot revealed a single pituitary PRL transcript, the expression of which was significantly reduced by E₂ treatment in adults but significantly increased in juvenile fish. In adult gonads four sbPRLR transcripts 1.1, 1.3, 1.9 and 2.8 kb were observed. A competitive RT-PCR was developed and used to determine how E₂ treatment alters expression of gonadal sbPRLR gene. Seabream PRLR was detectable in all samples analyzed by this assay and sbPRLR mRNA levels increased significantly (50-fold) after E₂ treatment in adults, but a 24-fold decrease was measured in juveniles. Immunohistochemistry using specific polyclonal antibodies raised against an oligopeptide from the extracellular domain of sbPRLR detected the receptor in spermatogonia and oocytes. Taken together the preceding results suggest that in the seabream PRL may act on both testis and ovary via its receptor and that the stage of maturity influences this process. The full characterization and relative importance of the different transcripts of sbPRLR on eliciting PRL action in the gonads remains to be elucidated.