Gamma-ray irradiation promotes premature meiosis of spontaneously differentiating testis–ova in the testis of p53-deficient medaka (Oryzias latipes)

In this study, the roles of p53 in impaired spermatogenic male germ cells of p53-deficient medaka were investigated by analyzing histological changes, and gene expressions of 42Sp50, Oct 4 and vitellogenin (VTG2) by RT-PCR or in situ hybridization in the testes. We found that a small number of oocyte-like cells (testis–ova) differentiated spontaneously in the cysts of type A and early type B spermatogonia in the p53-deficient testes, in contrast to the wild-type (wt) testes in which testis–ova were never found. Furthermore, ionizing radiation (IR) irradiation increased the number of testis–ova in p53-deficient testes, increased testis–ova size and proceeded up to the zygotene or pachytene stages of premature meiosis within 14 days after irradiation. However, 28 days after irradiation, almost all the testis–ova were eliminated presumably by p53-independent apoptosis, and spermatogenesis was restored completely. In the wt testis, IR never induced testis–ova differentiation. This is the first study to demonstrate the pivotal role of the p53 gene in the elimination of spontaneous testis–ova in testes, and that p53 is not indispensable for the restoration of spermatogenesis in the impaired testes in which cell cycle regulation is disturbed by IR irradiation.