Zebrafish androgen receptor is required for spermatogenesis and maintenance of ovarian function

Abstract

The androgen receptor (AR) is a nuclear receptor protein family member and inducible transcription factor that modulates androgen target gene expression. Studies using a mouse model confirmed the need for ar in reproductive development, particularly spermatogenesis. Here, we investigated the role of ar in zebrafish using CRISPR/Cas9 gene targeting technology. Targeted disruption of ar in zebrafish increases the number of female offspring and increases offspring weight. In addition, ar-null male zebrafish have female secondary sex characteristics. More importantly, targeted disruption of ar in zebrafish causes male infertility via defective spermatogenesis and female premature ovarian failure during growth. Mechanistic assays suggest that these effects are caused by fewer proliferated cells and more apoptotic cells in ar-null testes. Moreover, genes involved in reproductive development, estradiol induction and hormone synthesis were dys-regulated in testes and ovaries and the reproductive-endocrine axis was disordered. Our data thus suggest that the zebrafish ar is required for spermatogenesis and maintenance of ovarian function, which confirms evolutionarily conserved functions of ar in vertebrates, as well as indicates that ar-null zebrafish are a suitable model for studying pathologic mechanisms related to androgen disorders.

A high throughput zebrafish chemical screen reveals ALK5 and non-canonical androgen signalling as modulators of the pkd2−/− phenotype

“…S2b). These features are consistent with previously reported ar knockout zebrafish mutants [35][36][37] .…”

Shedding new light on early sex determination in zebrafish

“…This pattern of male-biased sex-expression in Sox9a can be seen in literature where it is reported to be predominantly expressed in the testis (Groh et al 2011 ). Many other studies support these findings that sox9a is a male sex-determining gene (Chiang et al 2001 ; Vidal et al 2001 ; Gasca et al 2002 ; Klüver et al 2005 ; Rodríguez-Marí et al 2005 ; Jørgensen et al 2008 ; Tong et al 2010 ; Major et al 2011 ; Sun et al 2013 ; Liu et al 2013 ; Chen et al 2017 ; Lin et al 2017b ; Yu et al 2018 ; Crowder et al 2018a ). Sox9a is expressed in early zebrafish development from 0–44 dpf (Jørgensen et al 2008 ), in the testis at juvenile stage, 30–44 dpf, and in fully developed adult stages (Zfin.org—ZFIN ID: ZDB-GENE-001103-1).…”

“…Fish embryos are an attractive model for the risk assessment of chemicals and for the investigation of effects of endocrine disrupting substances (Kazeto et al 2004 ; Yu et al 2018 ) and drug discovery (Vaz et al 2018 ). Toxicological studies which test acute toxicity by means of Fish Embryo Acute Test (FET) (OECD 2013 ) or Early-life Stage Toxicity Tests (ELS Test) (OECD 2010 ) often use zebrafish embryos as indicators of endpoints (Kazeto et al 2004 ; Yu et al 2018 ). At this early stage, the embryos cannot be morphologically sexed because during the test period sex differentiation is not yet complete (Kimmel et al 1995 ).…”

Zebrafish as an emerging model to study gonad development

“…In summary, homozygotic knockout zebrafishes or mutants of these testis-associated genes ( dmrt1 , amh and ar ) usually display a female-biased sex ratio [37] , [38] , [41] . In particular, abnormal expression of sox9a can block the ovary-testis transformation in zebrafish juvenile.…”

“…Hypertrophic testes with more germ cells and fewer spermatozoa are observed in homozygous amh mutated males, on account of uncontrollable proliferation and defective differentiation of the germ line [38] . ar -null male zebrafishes appear with female secondary sex characteristics and are sterile, having smaller testes and blocked spermatogenesis [41] . hsf5 −/− mutant males are infertile with decreased sperm count, abnormal sperm morphology and decreased sperm motility, however, females are fertile [40] .…”