Abstract
Wt1 encodes a zinc finger nuclear transcriptional factor, which is specifically expressed in testicular Sertoli cells and knockdown of Wt1 in Sertoli cells causes male mice subfertility. However, the underlying mechanism is still unclear. In this study, we found that expression of inhibin-α is significantly reduced in Wt1-deficient Sertoli cells. Luciferase assays using the inhibin-α promoter indicated that the inhibin-α promoter is transactivated by the Wt1 A, and B isoforms (−KTS), but not the C, and D isoforms (+KTS). Analysis of the Wt1 responsive element of the inhibin-α promoter region using site-directed mutagenesis showed that the nucleotides between −58 and −49 are essential for Wt1-dependent transactivation of the inhibin-α promoter. ChIP assays indicated that Wt1 directly interacts with the inhibin-α promoter. In addition, the inhibin-α promoter is activated synergistically by Wt1 and Sf1. Mutation of the ligand binding domain (LBD) of Sf1 (residues 235–238) completely abolished the synergistic action between Wt1 and Sf1, but did not affect the physical interaction between these two proteins, suggesting that other factor(s) may also be involved in the regulation of inhibin-α in Sertoli cells. Further studies demonstrated that β-catenin enhances the synergistic activation of Wt1 and Sf1 on the inhibin-α promoter. Given the fact that inhibin-α, a subunit of inhibin, is known to be involved in the regulation of spermatogenesis and testicular steroidogenesis, this study reveals a new regulatory mechanism of inhibin-α in Sertoli cells and also sheds light on the physiological functions of Wt1 in gonad development and spermatogenesis.
Highlights
Inhibins were first isolated and identified in gonadal fluids and extracts based on their ability to inhibit the synthesis and secretion of follicle-stimulating hormone (FSH) in the pituitary gland [1]
It has been reported that the expression of inhibin-a in granulosa cells is regulated by orphan nuclear receptor steroidogenic factor 1 (Sf1) [8,9], and cAMP [9]
We found that mutating the ligand binding domain (LBD) of Sf1 completely eliminated the synergistic activation of Wilms’ Tumor Gene 1 (Wt1) and Sf1 on the inihibin-a promoter (Fig. 6A)
Summary
Inhibins were first isolated and identified in gonadal fluids and extracts based on their ability to inhibit the synthesis and secretion of follicle-stimulating hormone (FSH) in the pituitary gland [1]. Inhibins are composed of two subunits, a common a subunit and one of two b subunits, A and B, encoded by separate genes [2,3]. Inhibin-a is expressed predominantly in ovarian granulosa cells and testicular Sertoli cells and has structural homology with transforming growth factor (TGF-b) [4,5,6,7]. It has been reported that the expression of inhibin-a in granulosa cells is regulated by orphan nuclear receptor steroidogenic factor 1 (Sf1) [8,9], and cAMP [9]. The Wt1 gene encodes a nuclear transcription factor which is predominantly expressed in kidneys, gonads, the spleen, and mesothelium during embryo development [11]. Wt1 expression is restricted to kidney podocytes, ovarian granulosa cells, and testicular Sertoli cells [12]. A number of growth and differentiation related genes, such as insulin-like growth factor II [15,16], insulin-like growth factor I receptor [17], platelet-derived growth factor A-chain [18,19], Pax-2 [20], syndecan-1 [21], Dax-1 [22], and amphiregulin [11,23,24], are regulated by Wt1
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
