AUTHOR=Safian Diego , van der Kant Henk J. G. , Crespo Diego , Bogerd Jan , Schulz Rüdiger W. 

TITLE=Follicle-Stimulating Hormone Regulates igfbp Gene Expression Directly or via Downstream Effectors to Modulate Igf3 Effects on Zebrafish Spermatogenesis

JOURNAL=Frontiers in Endocrinology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2017.00328

DOI=10.3389/fendo.2017.00328

ISSN=1664-2392

ABSTRACT=<p>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<sub>und</sub>) 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 <italic>igfbp</italic> transcript levels by Fsh and two of its downstream effectors, Igf3 and 11-ketotestosterone (11-KT). We also explored how Fsh-modulated <italic>igfbp</italic> 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 <italic>igfbp1a, -3</italic>, and <italic>-6a</italic> after 1 or 3 days, while increasing <italic>igfbp2a</italic> and <italic>-5b</italic> expression, but only after 5 days of incubation. Igf3 down-regulated the same <italic>igfbp</italic> transcripts as Fsh but with a delay of at least 4 days. 11-KT increased the transcripts (<italic>igfbp2a</italic> and <italic>5b</italic>) that were elevated by Fsh and decreased those of <italic>igfbp6a</italic>, as did Fsh, while 11-KT did not change <italic>igfbp1a</italic> or <italic>-3</italic> 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<sub>und</sub>, type A differentiating (A<sub>diff</sub>), or type B (B) spermatogonia). Igf3 (100 ng/mL) increased the area occupied by A<sub>diff</sub> and B while decreasing the one for A<sub>und</sub>. 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 <italic>igfbp</italic> expression in response to Fsh and adding or removing NBI-31772 at different times showed that the quick downregulation of three <italic>igfbp</italic> as well as the delayed upregulated of two <italic>igfbps</italic> all support Igf3 bioactivity, namely the stimulation of spermatogonial differentiation. We conclude that Fsh modulates, directly or <italic>via</italic> androgens and Igf3, <italic>igfbp</italic> gene expression, supporting Igf3 bioactivity either by decreasing <italic>igfbp1a, -3, -6a</italic> or by increasing <italic>igfbp2a</italic> and -<italic>5b</italic> gene expression.</p>