[Expression of a novel spermatogenesis gene SRG4 in postpartum normal and cryptorchid mouse testis]

To understand the function of SRG4, a novel spermatogenesis gene, we studied its expression pattern during normal mouse development and in experimental cryptorchidism. Testis tissues were collected from 1-, 3-, and 12-week-old normal mice and immunohistochemistry was used to detect the expression of SRG4. We performed surgery on mice to cre- ate unilateral cryptorchidism and monitored SRG4 mRNA levels by semi-quantitative RT-PCR in the cryptorchid testis from day 0-18. At post-operative day 18, the cryptorchid testis and the contralateral control testis were harvested and assayed for SRG4 expression by in situ hybridization. Immunohistochemistry results showed that SRG4 protein was hardly detected in 1-week-old mouse testis, but the expression was present in 3-week-old mouse and abundant in 12-week-old mouse testis. SRG4 immunostaining was mainly localized to the cytoplasm and membrane of spermatocytes and round spermatids. Moreover, semi-quantitative RT-PCR result showed the expression of SRG4 mRNA did not decrease until 9 d after cryptorchid surgery, and continued to decline thereafter. In situ hybridization revealed that in contrast to the abundant SRG4 expression in the control side, few remaining germ cells in the crytorchid testis were positive for SRG4 at d 18 after surgery. The results indicated that the expression of SRG4 was regulated by development, and SRG4 was mainly expressed in the cytoplasm of spermatocytes and round spermatids. However, in cryptorchid testis, in which most germ cells undergo apoptosis, only a few of SRG4 is observed, suggesting that SRG4 may be as a specific marker to evaluate the process of spermatogenesis.