Differential splicing of three gonadotropin-releasing hormone transcripts in the ovary of seabream (Sparus aurata).

Previous studies demonstrated the presence of high-affinity GnRH binding sites and compounds with GnRH-like activity in the ovary of seabream, Sparus aurata, providing evidence for the role of GnRH as a paracrine/autocrine regulator of ovarian function in this species. In the present study, the expression of three forms of GnRH (salmon, chicken-II, and seabream) genes in this marine teleost species was demonstrated for the first time. Moreover, there is evidence for differential splicing and intronic expression of cGnRH-II and sbGnRH. Treatment of seabream follicle-enclosed oocytes with salmon GnRH stimulated reinitiation of oocyte meiosis, whereas chicken GnRH-II treatment was without effect. Novel information was also provided about organization of cGnRH-II and seabream GnRH transcripts, confirming that GnRH gene organization is maintained through evolution, despite changes in the size and sequence of exons and introns.