Cbx3hypo/hypotestes showed a dramatic loss in the number of germ cells. (a,b) Typical germ cell nuclear antigen (GCNA) staining of germ cells within wild-type testes. (c,d) In Cbx3hypo/hypotestes, there was a dramatic reduction in the numbers of GCNA-positive germ cells. Some tubules contained no GCNA-positive germ cells and presented a Sertolin cells-only phenotype (asterisk). Bar = 100 μm.