Figure 12

A comparison of retinoic acid metabolism in the embryonic urogential system of the mouse and chicken. RALDH2-expressing tissue is shown in red, CYP26B1-expressing tissue is shown in green; tissues expressing both enzyme mRNAs are shown in yellow. In the mouse at E12.5, Raldh2 is expressed in the mesonephric kidney, retinoic acid then enters the gonad and in males, is degraded by Cyp26b1. In females, Cyp26b1 is absent, allowing retinoic acid to induce germ cells meiosis. In the chicken at E14.5, the gonads of both sexes express RALDH2. In males, RALDH2 and CYP26B1 are co-expressed in seminiferous cords. In the cortex of the left female gonad, where germ cells are located, RALDH2 is expressed but CYP26B1 is not (CYP26B1 expression is localised at the border between the cortex and medulla). In the right gonad, as in the testis, both RALDH2 and CYP26B1 are expressed, potentially leading to retinoic acid degradation and no meiosis.