Insulin-like 3 affects zebrafish spermatogenic cells directly and via Sertoli cells

Diego Crespo,Birgitta Norberg,Yung-Ching Choi,Marjo J Den Broeder,Yu Ting Zhang,Jan Bogerd,Diego Safian,Rüdiger W Schulz,Kai Ove Skaftnesmo,Tomasz Furmanek,Luiz H C Assis,Juliette Legler,Wei Ge

doi:10.1038/s42003-021-01708-y

Abstract

Pituitary hormones can use local signaling molecules to regulate target tissue functions. In adult zebrafish testes, follicle-stimulating hormone (Fsh) strongly increases the production of insulin-like 3 (Insl3), a Leydig cell-derived growth factor found in all vertebrates. Little information is available regarding Insl3 function in adult spermatogenesis. The Insl3 receptors Rxfp2a and 2b were expressed by type A spermatogonia and Sertoli and myoid cells, respectively, in zebrafish testis tissue. Loss of insl3 increased germ cell apoptosis in males starting at 9 months of age, but spermatogenesis appeared normal in fully fertile, younger adults. Insl3 changed the expression of 409 testicular genes. Among others, retinoic acid (RA) signaling was up- and peroxisome proliferator-activated receptor gamma (Pparg) signaling was down-regulated. Follow-up studies showed that RA and Pparg signaling mediated Insl3 effects, resulting in the increased production of differentiating spermatogonia. This suggests that Insl3 recruits two locally active nuclear receptor pathways to implement pituitary (Fsh) stimulation of spermatogenesis.

Highlights

Pituitary hormones can use local signaling molecules to regulate target tissue functions
Follow-up studies showed that both, human Insulin-like 3 (INSL3) and zebrafish Insl[3], stimulated the differentiating proliferation of type A undifferentiated (Aund) spermatogonia, while no direct effect was found on testicular androgen production in zebrafish[20,23]
We analyzed rxfp2a and rxfp2b transcript levels in an RNA sequencing (RNAseq) dataset that compared control, germ cell-depleted, and recovering testis tissue[25], to obtain information on the identity of receptor expressing cells. rxfp2a expression was enriched in germ cells, since its transcript levels were low in germ cell-depleted testes and increased to control levels during the recovery of spermatogenesis (Fig. 1B). rxfp2b expression, on the other hand, remained unchanged following germ cell depletion and subsequent recovery of spermatogenesis (Fig. 1B), suggesting that the rxfp2b transcript is mainly expressed by somatic cells in zebrafish testis

Summary

Introduction

Pituitary hormones can use local signaling molecules to regulate target tissue functions. Follow-up studies showed that RA and Pparg signaling mediated Insl[3] effects, resulting in the increased production of differentiating spermatogonia. This suggests that Insl[3] recruits two locally active nuclear receptor pathways to implement pituitary (Fsh) stimulation of spermatogenesis. Follow-up studies showed that both, human INSL3 and zebrafish Insl[3], stimulated the differentiating proliferation of type A undifferentiated (Aund) spermatogonia, while no direct effect was found on testicular androgen production in zebrafish[20,23] These studies suggest that Fsh-induced stimulation of spermatogenesis is mediated, at least in part, by Insl[320]. The Insl3-mediated up-regulation of RA signaling as well as the down-regulation of Pparg signaling both promoted the production of differentiating spermatogonia, identifying two nuclear receptor pathways to mediate testicular growth factor signaling in response to a pituitary gonadotropin

Methods

Results

Conclusion