Transplantation of RCFG cells to immunodeficient recipients. A) A lacZ reporter gene construct was introduced into RCFG cells using a lentiviral vector. After antibiotic selection, lacZ expression in RCFG cells was confirmed with X-gal staining. B–E). Seminiferous tubules of recipient testes transplanted with the lacZ-expressing RCFG cells. Recipient testes were analyzed with X-gal staining at 7, 16, and 23 wk after transplantation. Donor RCFG cells were stained blue. B, C) At 7 wk after transplantation, blue cells were found, including doublets. D) At 16 wk after transplantation, small clusters of blue cells were found. E) At 23 wk after transplantation, blue cell clusters were spread. F) Histological examination of a recipient testis at 23 wk. Recipient testis was stained with X-gal, sectioned, and counterstained with nuclear fast red. Blue donor cells were found on the basement membrane (arrows). Scale bars = 50 μm (A); 100 μm (B); 25 μm (C–F).