Seasonal expression and cellular distribution of star and steroidogenic enzymes in quail testis

The quail Coturnix coturnix is a seasonal breeder with a physiological switch on/off of gonadic activity. Photoperiod and temperature are the major environmental factors regulating the spermatogenesis. To more thoroughly comprehend the steroidogenic pathways that govern the seasonal reproductive cycle, we have investigated the localization of StAR protein and steroidogenic enzymes (3β‐HSD, 17β‐HSD, P450 aromatase, and 5α‐Red) as well as androgen and estrogen levels, in the testis of reproductive and nonreproductive quails. We demonstrated that StAR, 3β‐HSD, 17β‐HSD, P450 aromatase, and 5α‐Red were always present in the somatic (Leydig and Sertoli cells) and germ cells (spermatogonia, spermatocytes I and II, spermatids, and spermatozoa). In addition, by western blot analysis, we demonstrated that 17β‐HSD, P450 aromatase, and 5α‐Red showed the highest expression levels during the reproductive testis compared with nonreproductive one. Accordingly, we also found that during the reproductive phase the highest titres of testosterone, 17β‐estradiol, and 5α‐dihydrotestosterone are recorded. In conclusion, our findings demonstrated that in C. coturnix: (a) both somatic and germ cells are involved in the local synthesis of sex hormones; (b) 17β‐HSD, P450 aromatase, and 5α‐Red expressions, as well as testicular androgens and estrogens, increased in reproductive quail testis. This study strongly indicates that the steroidogenic process in quail testis exhibits seasonal changes with the promotion of both androgenic and estrogenic pathways in the reproductive period, suggesting their synergic mechanism in the spermatogenesis regulation. Research Highlights In the quail, StAR and steroidogenic enzymes are always present in the somatic and germ cells. The steroidogenic process in quail testis exhibits seasonal changes. Androgenic and estrogenic pathways are promoted in the reproductive period. The upper panel shows western blot detection of 17β‐HSD, P450 arom, and 5α‐Red proteins in the testis from reproductive and nonreproductive quails. Specific bands corresponding to the sizes of 35 kDa (17β‐HSD), 58 kDa (P450 arom), and 28 kDa (5α Red) were detected; lower panel, the amounts of 17β‐HSD, P450 arom, and 5α Red were quantified using the ImageJ program and normalized with respect to β‐actin (see upper panel). Values represent the means ± standard deviation of five samples (two bands shown in upper panel). *p