Histological sections of targeted mice. (A) Testis of wild-type and GATA-1^–-tg mice. Hematoxylin-eosin staining of testis section. (i) Wild-type and (iii) GATA-1^–-tg. Gross histology of testis section was unremarkable. GATA-1 antibody (N6) staining of testis section. (ii) Wild-type, (iv) GATA-1^–-tg. GATA-1 signals were detected in Sertoli cells in wild-type (white arrow) but were absent in GATA-1^–-tg testis. (B) Histology of yolk sac. Hematoxylin-eosin staining of E8.5 YS paraffin sections. Wild-type (i), GATA-1^– (ii), GATA-2^–/– (iii), GATA-1^–//GATA-2^–/– double-knockout (iv-vi) YS, and GATA-1^–//GATA-2^–/– double-knockout-tg (ix), stained E9.5 YS paraffin section. GATA-1^–//GATA-2^–/– double-knockout and SCL/tal1^–/– (viii). Note that the double-knockout YS has no evident blood cells (iv-vi); however, the double-knockout with the rescue tg has blood cells in the vascular plexus (ix). Cell masses evident in the vascular plexus of the double-knockout (vii) and SCL/tal-1^–/– (viii) at E9.5 consist of tightly packed clusters without round hematopoietic cells. Arrow (iv) indicates abnormal cell mass in double-knockout YS. Arrows (v, vi, viii) indicate apoptotic cells.