Fig. 2. Sox9 or Sox8/Sox9 knock-out mice show defects in sex cord formation. E13.5 gonads from Sox9 tissue-specific knock-out animals show a variable degree of sex cord formation ranging from normal (not shown) to severely abnormal (arrow in C). Note the presence of abnormal vascularization (arrowhead in C). Sox8/Sox8 knock-out gonads develop normal testis cords (D). By contrast, Sox9 tissue-specific knock-out animals (Cre/+ Sox9^flox/Sox9^flox) either heterozygous (E) or homozygous (F) for the Sox8 knock-out allele often show complete absence of sex cord formation. (For frequencies of abnormal gonadal development see Table 1.)