Fig. 4. Spermatogenesis and the generation of offspring from GS cells. EGFP-expressing GS cells from 24-month-old cultures were transplanted into the seminiferous tubules of infertile W recipient mice. (A) A recipient testis showing the EGFP fluorescence in GS cell-derived colonies. Green tubules represent donor GS cell colonization. (B) Histological analysis (Hematoxylin and Eosin staining) of the recipient testis showing normal-appearing spermatogenesis. (C) Round spermatid released from a recipient testis, exhibiting EGFP fluorescence (arrow). (D) Offspring resulting from the microinjection of oocytes with round spermatids, exhibiting fluorescence. Scale bar: 1 mm.