Augmentation of progestin signaling rescues testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling

Disruption of androgen signaling is known to cause testicular malformation and defective spermatogenesis in zebrafish. However, knockout of cyp17a1, a key enzyme responsible for the androgen synthesis, in ar-/- male zebrafish paradoxically causes testicular hypertrophy and enhanced spermatogenesis. Because Cyp17a1 plays key roles in hydroxylation of pregnenolone and progesterone (P4), and converts 17 alpha-hydroxypregnenolone to dehydroepiandrosterone and 17 alpha-hydroxyprogesterone to androstenedione, we hypothesize that the unexpected phenotype in cyp17a1-/-;androgen receptor (ar)-/- zebrafish may be mediated through an augmentation of progestin/nuclear progestin receptor (nPgr) signaling. In support of this hypothesis, we show that knockout of cyp17a1 leads to accumulation of 17 alpha,20 beta-dihydroxy-4-pregnen-3-one (DHP) and P4. Further, administration of progestin, a synthetic DHP mimetic, is sufficient to rescue testicular development and spermatogenesis in ar-/- zebrafish, whereas knockout of npgr abolishes the rescue effect of cyp17a1-/- in the cyp17a1-/-;ar-/- double mutant. Analyses of the transcriptomes among the mutants with defective testicular organization and spermatogenesis (ar-/-, ar-/-;npgr-/- and cyp17a-/-;ar-/-;npgr-/-), those with normal phenotype (control and cyp17a1-/-), and rescued phenotype (cyp17a1-/-;ar-/-) reveal a common link between a downregulated expression of insl3 and its related downstream genes in cyp17a-/-;ar-/-;npgr-/- zebrafish. Taken together, our data suggest that genetic or pharmacological augmentation of the progestin/nPgr pathway is sufficient to restore testis organization and spermatogenesis in zebrafish with the depletion of androgen signaling.

Automated summary

Disruption of androgen signaling in zebrafish can lead to testicular malformation and defective spermatogenesis. However, knockout of cyp17a1, a key enzyme responsible for androgen synthesis, paradoxically causes testicular hypertrophy and enhanced spermatogenesis. This unexpected phenotype may be mediated through the progestin/nPgr signaling pathway. Knockout of cyp17a1 leads to the accumulation of certain hormones and administration of progestin can rescue testicular development and spermatogenesis in zebrafish. The downregulation of insl3 and related genes may play a role in the impaired testicular organization and spermatogenesis observed in cyp17a-/-;ar-/-;npgr-/- zebrafish.