Stage-specific expression of Gadd45 induced by X-irradiation in rat spermatogenesis

Purpose : Gadd45 is involved in the response to DNA damage in somatic cells. The effect of X-irradiation and chemical treatments on expression of Gadd45 and two other 53-regulated genes, p21 and cyclin-G, was studied in rat testis. Materials and methods : The reverse-transcriptase polymerase chain reaction (RT-PCR) was performed on testis extracts of control, X-irradiated (6Gy), etoposide (10 mg kg -1) and adriamycin (5mg kg -1) -treated rats. For stage-specific analysis, seminiferous tubules were isolated and segments representing the 14 epithelial stages were obtained. Results : In whole testis extracts, increases in Gadd45, p21 and cyclin-G expression were detectable after irradiation, but not after etoposide or adriamycin treatments. Analysis of fractions consisting of defined epithelial stages showed a high expression of Gadd45 in stages VII-XII and of p21 in stages VII-VIII. Irradiation significantly increased the level of Gadd45 mRNA in stages VI-VIII and of p21 mRNA in stages VI-I. Although no overall increase could be observed in whole testis samples of the etoposide-treated rat, stage-specific analysis revealed an induction of p21 expression in stages XIII-I. Gadd45 and cyclin-G mRNA were localized to spermatocytes and round spermatids known to express p21. Conclusions : Although X-irradiation, etoposide and adriamycinare known spermatogenic mutagens and activators of apoptosis, only X-rays induce slightly Gadd45 expression in testis. This small induction was very stage specific.