Follicle-Stimulating Hormone Regulates Gene Expression Directly or Downstream Effectors to Modulate Igf3 Effects on Zebrafish Spermatogenesis.

Previous work showed that pharmacological inactivation of Igf-binding proteins (Igfbps), modulators of Igf activity, resulted in an excessive differentiation of type A undifferentiated (A) spermatogonia in zebrafish testis in tissue culture when Fsh was present in the incubation medium. Using this testis tissue culture system, we studied here the regulation of transcript levels by Fsh and two of its downstream effectors, Igf3 and 11-ketotestosterone (11-KT). We also explored how Fsh-modulated expression affected spermatogonial proliferation by adding or removing the Igfbp inhibitor NBI-31772 at different times. Fsh (100 ng/mL) decreased the transcript levels of , and after 1 or 3 days, while increasing and expression, but only after 5 days of incubation. Igf3 down-regulated the same transcripts as Fsh but with a delay of at least 4 days. 11-KT increased the transcripts ( and ) that were elevated by Fsh and decreased those of , as did Fsh, while 11-KT did not change or transcript levels. To evaluate Igfbps effects on spermatogenesis, we quantified under different conditions the mitotic indices and relative section areas occupied by the different spermatogonial generations (type A, type A differentiating (A), or type B (B) spermatogonia). Igf3 (100 ng/mL) increased the area occupied by A and B while decreasing the one for A. Interestingly, a concentration of Igf3 that was inactive by itself (25 ng/mL) became active in the presence of the Igfbp inhibitor NBI-31772 and mimicked the effect of 100 ng/mL Igf3 on spermatogonia. Studies exploiting the different dynamics of expression in response to Fsh and adding or removing NBI-31772 at different times showed that the quick downregulation of three as well as the delayed upregulated of two all support Igf3 bioactivity, namely the stimulation of spermatogonial differentiation. We conclude that Fsh modulates, directly or androgens and Igf3, gene expression, supporting Igf3 bioactivity either by decreasing or by increasing and - gene expression.