Expression of sGnRH mRNA in gonads during rainbow trout gametogenesis

The salmon gonadotropin-releasing hormone (sGnRH) is the major form of GnRH decapeptide expressed in the salmonid brain and it acts as a gonadotropin releaser. In rainbow trout, sGnRH-1 and sGnRH-2 mRNA forms were found in br ain and gonads. We analyzed the expression of both forms in trout gonads at different stages of gametogenesis. Northern blot demonstrated that sGnRH-2 mRNA was the major sGnRH form in testis and ovary. In testis but not in ov ary, brain or pituitary, alternatively spliced sGnRH-2 transcripts which co ded for prepro-sGnRH with a truncated GnRH-associated peptide due to a prem ature stop codon in retained intron 2 were detected. In testis, sGnRH mRNA was highly expressed before the onset of spermatogenesis, it disappeared at stage II and then increased progressively up to stage VI. In ovary, the ex pression of sGnRH was high in immature pre-vitellogenic fish and progressiv ely decreased throughout vitellogenesis. At ovulation it reached its maximu m and came down again after stripping. The decrease of sGnRH mRNA expressio n during the period of active spermatogonial proliferation in testis and in crease during meiosis occurrence in testis and ovary suggest an anti-prolif erative and meiosis-stimulating effect of sGnRH during rainbow trout gameto genesis. (C) 2001 Elsevier Science Inc. Ah rights reserved.