Retinoic acid signaling determines the fate of uterine stroma in the mouse Müllerian duct

Abstract

The Müllerian duct develops into the oviduct, uterus, and vagina, all of which are quite distinct in their morphology and function. The epithelial fate of these female reproductive organs in developing mice is determined by factors secreted from the stroma; however, how stromal differentiation occurs in the female reproductive organs derived from the Müllerian duct is still unclear. In the present study, roles of retinoic acid (RA) signaling in developing female reproductive tracts were investigated. Retinol dehydrogenase 10 (RDH10) and aldehyde dehydrogenase family 1 subfamily A2 (ALDH1A2) mRNAs and proteins and transactivation activity of endogenous RA were found in the stroma of proximal Müllerian ducts and gradually decreased from the proximal to caudal regions in fetal mice. In organ-cultured Müllerian ducts, retinaldehyde or RA treatment induced uterine epithelial differentiation, defined as a layer of columnar epithelial cells negative for oviductal and vaginal epithelial markers. In contrast, inhibition of RA receptor (RAR) signaling induced vaginal epithelial differentiation, characterized as vaginal epithelial marker genes–positive stratified epithelium. Grafting experiments of the organ-cultured Müllerian duct revealed irreversible epithelial fate determination. Although RAR did not directly bind to the homeobox A10 (Hoxa10) promoter region, RA–RAR signaling stimulated Hoxa10 expression. Thus, RA–RAR signaling in the Müllerian duct determines the fate of stroma to form the future uterus and vagina.

Physiological and pathological implications of retinoid action in the endometrium

“…This hypothesis was confirmed in a reporter mouse expressing lacZ regulated by a strong RARE in the promoter. The data demonstrated that the highest endogenous RA levels are in the proximal Müllerian duct stroma, and the levels gradually decrease from the proximal to caudal regions (Nakajima et al 2016). Thus, RA is produced and acts in the stroma of proximal and middle Müllerian ducts.…”

“…In fetal mice, Rdh10 and Aldh1a2 are expressed in the stroma of proximal Müllerian ducts, with expression levels decreasing toward the caudal ends (Nakajima et al 2016). RDH10 is the primary enzyme responsible for catalyzing the conversion of retinol to retinaldehyde, the first step of RA synthesis, in embryonic mice (Farjo et al 2011).…”

“…Thus, RA is produced and acts in the stroma of proximal and middle Müllerian ducts. Rdh10 and Aldh1a2 expression are significantly higher in the uteri of postnatal mice than those in their vaginas from postnatal day 2 (P2) to P90 (Nakajima et al 2016). Moreover, mice fed from birth with vitamin A-deficient diets for 10 or 14 weeks exhibit squamous metaplasia in their uterine epithelia (Darwiche et al 1993, Jetten et al 1996.…”

“…By contrast, inhibition of RAR signaling with the pan-RAR antagonist AGN193109 (AGN; Nakajima et al 2016) induces vaginal epithelial differentiation. Nakajima et al (2016) cultured Müllerian duct explants at E14.5 or E17.5 with RA or RAR antagonists and grafted these under the renal capsules of host mice. At day 30 post grafting, control E14.5 Müllerian ducts developed oviductal and uterine epithelia, while AGN treatment irreversibly induced vaginal epithelia.…”

“…The expression of these same genes can be modulated by ovarian steroid hormones (i.e., estradiol and progesterone) treatment (Vermot et al 2000, Li & Ong 2003, Rühl et al 2006, Fritzsche et al 2007). The retinoid pathway is known to play vital roles in endometrial development and differentiation (Tanmahasamut & Sidell 2005, Wu et al 2013, Nakajima et al 2016, as well as endometrial neovascularization (Sidell et al 2010) and blastocyst implantation (Han et al 2010, Ma et al 2012.…”