The Egr family of zinc finger transcription factors is rapidly induced by various mitogens and regulates cell growth, differentiation, and apoptosis. While it is clear that loss of Egr1 leads to anovulatory infertility due to LHβ deficiency in female mice, molecular function of Egr1 in male reproduction has not been clearly investigated. Here, we demonstrate that Egr1 acts as an intrinsic transcription factor in Leydig cells to regulate their proliferation and steroidogenesis in the testis as well as an extrinsic factor for male reproduction via LHβ transcription in the pituitary. Egr1 is predominantly expressed in spermatogonia and Leydig cells in immature testes and later detected in some of these cell types in mature testes. The fertility potential of Egr1(-/-) male mice is relatively deteriorated even at 2 month-old age and aggravated with aging. The incidence of abnormalities of seminiferous tubules such as Sertoli cell only was dramatically increased with aging. The number and mean size of Leydig cells were significantly reduced in Egr1(-/-) testes. The impairment of Leydig cells is consistent with significant reduction in levels of testosterone and expression of factors critical for steroidogenesis such as StAR in Egr1(-/-) testes. Exogenous administration of hCG rapidly and transiently induced Egr1 expression in Leydig cells culture in vitro. hCG could reinstate reduced mean size of Leydig cells but not reduced number of Leydig cells and aberrantly low StAR expression, suggesting that Egr1 has critical functions for Leydig cell proliferation and their steroidgenesis. In addition, daily sperm production and in vitro fertilization (IVF) competence were significantly reduced, and apoptosis was facilitated in these mice. Furthermore, hCG administration to compensate for relatively low LH levels in Egr1(-/-) males could not restore the compromised reproductive phenotypes such as IVF competence and apoptosis in these mice. Interestingly, expression of Egr2, a member of Egr family, is significantly elevated in Egr1(-/-) Leydig cells suggesting that genetic compensation of Egr2 may alleviate phenotypic aberration of Egr1(-/-) male testes. Collectively, these results suggest that Egr1 act as an intrinsic transcription factor required for proliferation and steroidogenesis of Leydig cells to govern spermatogenesis in the testis.

Aquaporin 5 (AQP5) implicated in the generation of saliva, tears, and pulmonary secretions functions as a water-specific channel. Epididymal epithelial cells actively reabsorb water, ions and proteins. Large quantity of testicular fluid movement across the epididymal tubules generates high osmotic milieu which is important for sperm maturation. In an effort to understand the fluid homeostasis and its regulation by sex steroids in male reproductive tract, the expression of AQP5 was examined in different regions of mouse epididymis during postnatal development. The effect of androgen on the expression of epididymal AQP5 was examined in ORX model. AQP5 mRNA levels were the highest in corpus region in which drastic increase was noted during sexual maturation. Epididymal AQP5 immunoreactivity was largely found in apical as well as basal region of luminal epithelia. Moderate immunoreactivity for AQP5 was found in in smooth muscle cells in both immature and mature mice. Epididymal lumen of ORX mice showed shrinkage together with decrease in AQP5 expression. Alteration of AQP5 expression in ORX epididymis was partially recovered by androgen injection. AQP5 mRNA was induced at 10uM 5α-DHT in organ cultured epididymis. Chromatin immunoprecipitatin (ChIP) showed that 5α-DHT induced recruitment of androgen receptor (AR) to the －4635 to －4453 bp region of the AQP5 gene promoter in adult epididymis. Taken together, axial regulatory mechanism may control transcription of AQP5 along the length of epididymal tubule. Water transport through AQP5 is important for late sperm maturation and storage in epididymis. Androgen may directly induce AQP5 gene transcription via activation of AR in epididymis.

Foxi1, a forkhead family of transcription factor, in narrow and clear cells in epididymis is required for male fertility through regulating transcription of vacuolar H+-ATPase. To understand the regulation of Foxi1 gene activation in epididymis, the effects of steroids and their receptor antagonists and testicular factors on the expression of Foxi1 in epididymal segments were examined in mouse. Epididymis were sampled from adult mice following injections of ICI 182,780 (5mg/head, 2 times for 15 days), dexamethasone (DEX, 0.1,1,10ug/kg/day for 5 days) or oral administration of flutamide (FLM, 100mg/kg/day for 10 days). Otherwise, adult mice were orchidectomized (ORX), rested for 2 weeks, and received testosterone propionate(TP, 3mg/kg/day) for 7 days. In addition, adult male mice were subjected to efferent duct ligation (EDL) and epididymis was collected after 15 days. To study estrogen regulation of Foxi1 gene activation via estrogen receptor α (ESR1), Foxi1 expression was examined in ESR1 knock-out mice epididymis. Expression and subcellular localization of Foxi1 was analyzed by realtime RT-PCR and immunohistochemistry. To search transcription factor binding in the mouse Foxi1 gene promoter, in silico analysis was performed using TESS, TFSEARCH, and Gene-Regulation. ICI 182,780 significantly decreased Foxi1 mRNA levels in caput and corpus but increased in cauda epididymis. Foxi1 mRNA levels in caput epididymis of ESR1 KO mice were significantly lower than those of WT mice, but no significantly changed in corpus and cauda epididymis. Taken together, estrogen differentially regulates Foxi1 gene expression in epididymis. In ORX mice, Foxi1 mRNA levels were significantly increased in epididymis, and which was abrogated by TP. Though FLM did not significantly alter the Foxi1 mRNA levels, androgen may affect Foxi1 gene expression in epididymis. DEX significantly decreased Foxi1 mRNA levels in caput and corpus epididymis at 0.1ug/kg/day and in cauda epididymis at 1ug/kg/day, suggesting that glucocorticoid may negatively regulate Foxi1 gene expression. No significant change in Foxi1 mRNA levels was found after EDL. Foxi1 immunoreactivity was found in the nuclei of narrow cells of caput epididymis including initial segment and clear cells of corpus and cauda epididymis. Of note, in ORX mice, Foxi1-positive narrow cells and clear cells were increased, and which was abrogated by TP. In silico analysis revealed the presence of putative binding sequences for ESR1, AR, and GR in the 5’ upstream region from the Foxi1 promoter. In conclusion, the expression of Foxi1 in narrow cells in caput epididymis might be positively regulated by estrogen via ESR1, which was different from estrogen–ESR signaling in clear cells in corpus and cauda epdididymis. Androgen and glucocorticoid may negatively regulate expression of Foxi1 in all epdididymial segments.