Molecular mechanism of the differentiation and tissue formation from the common primordium of adrenal cortex and gonads.

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The expression profiles of Ad4BP/SF-1 in rat embryos demonstrated that steroid-hormone-producing cells of adrenal cortex and gonads are derived from a common precursor named the "adreno-genital primordium". To address the question of the molecular mechanism that underlies the differentiation of the adrenal cortex and gonads, we raised new antibodies against some of the differentiation related factors (Pref-1/ZOG, WT1, Ad4BP/SF-1, Emx2), and examined the expression of these factors and the relationship to other factors. Pref-1 was expressed in the adreno-genital primordium slightly wider than Ad4BP/SF1. The expression of Pref-1 decreased during the differentiation of adrenal cortex and gonads, and Pref-1 was supposed to have function to keep cells in undifferentiated state. In the adult adrenal cortex, the expression of Pref-1 is restricted to the zona glomerulosa, whereas the expression of adrenal inner zone antigen (IZA) was restricted to the zona fasciculata and zona reticularis. The expression profiles of Pref-1 and IZA was complementary. IZA was found to bound a haem chromophore and was identical with membrane-associated progesterone receptor (MPR). IZA enhanced progesterone 21-hydroxylase reaction. Pref-1 was also found to be abundantly expressed in pituitary. Emx2 is essential for the formation of gonads. Emx2 was also expressed in the marginal zone of cerebral cortex and essential for the survival of reelin-positive cells, whereas Pax6 was also involved in the specification of reelin-positive cells in the cortical marginal zone, potentially in a manner opposite to the positive role of Emx2.