The nuclear receptor steroidogenic factor 1 (Sf1, Nr5a1, Ad4bp) is critical for formation, development and function of steroidogenic tissues. A fetal adrenal enhancer (FAdE) in the Sf1 gene was previously identified to direct Sf1 expression exclusively in the fetal adrenal cortex and is bound by both Sf-1 and Dax1. Here, we examined the function of Sf1 SUMOylation and its interaction with Dax1 on FAdE function. A diffused prolonged pattern of FAdE expression and delayed regression of the postnatal fetal cortex (X-zone) were detected in both the SUMOylation deficient-Sf12KR/2KR and Dax1 knockout mouse lines, with FAdE expression/activity retained in the postnatal 20αHSD positive postnatal X-zone cells. In vitro studies indicated that Sf1 SUMOylation, while not directly influencing DNA binding, actually increased binding of Dax1 to Sf1 to further enhance transcriptional repression of FAdE. Taken together, these studies define a critical repressor function of Sf1 SUMOylation and Dax1 in the physiologic cessation of FAdE mediated Sf1 expression and the resultant regression of the postnatal fetal cortex(X-zone).
