Fig. 7. Arrest of spermatogenesis in the PU.1 mutant gonad. (Aa-h) Wild-type E18.5 testes (a,c,e,g) and testes of their PU.1^G/G littermates (b,d,f,h) were dissected and grafted under the tunica albuginea of recipient nude mice. Histological analysis and PCNA immunostaining were performed 1 week after transplantation. The contorted shape of the peripheral labeled nuclei in h is a known characteristic of Sertoli cells. (Ba-d) The same analysis 4 weeks after grafting. At low magnification, the limit of the graft (upper left) and the host tissue (lower right) can be seen in a and b, corresponding in b to that between empty tubules and normal spermatogenesis. Scale bars: 200 µm in Aa,Ab,Ba,Bb; 50 µm in all other panels.