Preliminary evidence suggesting variations of GtH 1 and GtH2 mRNA levels at different stages of gonadal development in rainbow trout, Oncorhynchus mykiss.

To study the variations of alpha and beta GtH 1 and 2 gene expression during gonadal development in male and female rainbow trout, chum salmon alpha and beta GtH 1 and 2 probes were used. The alpha subunit cDNA probe used is identical to the cDNA encoding the alpha subunit common to both GtH 1 and 2. Total RNAs were prepared from pooled pituitaries and the validation of the use of these probes for studying the variation of GtH mRNAs was made by Northern blot analysis. The quantitative determination of GtH mRNAs employed slot blot hybridization. In males and females, beta GtH 1 predominates in early stages of gonadal development (spermatogonia A and previtellogenesis), beta GtH 2 being weakly expressed. Both beta GtH 1 and beta GtH 2 are expressed during prespermiation, spermiation, and the periovulatory period with a predominance of beta GtH 2. In both sexes alpha GtH variations follow beta GtH 2 variations.