Induced differentiation of ovine foetal gonocytes after grafting in the scrotum of nude mice.

This work was designed to elucidate, in foetal ovine testis, whether the reason why gonocytes do not differentiate into spermatogonia and do not initiate spermatogenesis is due to inadequate foetal environment (temperature and/or hormonal balance) or if somatic testicular cell proliferation is a prerequisite for initiation of male meiosis. The development and differentiation of gonocytes were analysed by grafting 60-day-old foetal ovine tests into the scrotum of immunotolerant adult Nude mice. Forty days after grafting, nine of the ten grafted testes had survived but had not increased in weight as compared to 60-day-old tests. Moreover, only one third of the graft was occupied by testicular tissue, in which the relative proportions of intertubular tissue and sex cords were not altered when compared with those of normal foetal testes. The remainder of the graft was occupied by teratoma. The total number of Leydig (-80%) cells, Sertoli (-66%) cells, gonocytes (-90%) and the total length of sex cords (-63%) per grafted testis were always significantly reduced (P < 0.02), whereas the sex cords were significantly increased in diameter (+36%; P = 0.02) as compared to those of non-grafted 60-day-old foetuses. However, in seven out of the nine testes, type A spermatogonia were obtained and in two of the seven a few type B or leptotene primary spermatocytes could be observed. The grafting of foetal testis in an adult scrotum induces differentiation of gonocytes into spermatogonia, independently of proliferation of Sertoli and Leydig cells.