Genome-wide identification of FOXL2 binding and characterization of FOXL2 feminizing action in the fetal gonads

Abstract

The identity of the gonads is determined by which fate, ovarian granulosa cell or testicular Sertoli cell, the bipotential somatic cell precursors choose to follow. In most vertebrates, the conserved transcription factor FOXL2 contributes to the fate of granulosa cells. To understand FOXL2 functions during gonad differentiation, we performed genome-wide analysis of FOXL2 chromatin occupancy in fetal ovaries and established a genetic mouse model that forces Foxl2 expression in the fetal testis. When FOXL2 was ectopically expressed in the somatic cell precursors in the fetal testis, FOXL2 was sufficient to repress Sertoli cell differentiation, ultimately resulting in partial testis-to-ovary sex-reversal. Combining genome-wide analysis of FOXL2 binding in the fetal ovary with transcriptomic analyses of our Foxl2 gain-of-function and previously published Foxl2 loss-of-function models, we identified potential pathways responsible for the feminizing action of FOXL2. Finally, comparison of FOXL2 genome-wide occupancy in the fetal ovary with testis-determining factor SOX9 genome-wide occupancy in the fetal testis revealed extensive overlaps, implying that antagonistic signals between FOXL2 and SOX9 occur at the chromatin level.

Increased FOXL2 Expression Alters Uterine Structures and Functions

“…The Rosa26-CAG-LSL-Foxl2 mice with FOXL2 overexpression (named as Foxl2 LsL/+ in this paper), and Pgr cre mice were described previously [13, 27]. Ltf icre mice were kindly provided by Dr. Sudhansu K. Dey [28].…”

“…Increased Foxl2 expression was achieved by crossing mice with a conditionally active transgene, Foxl2 LsL/+ [13] with the Pgr cre allele [27] generating the Pgr cre/+ Foxl2 LsL/+ (FOXL2 OE ) mouse. Immunohistochemical analysis was used to detect the expression of endogenous FOXL2 and the Foxl2 transgene in the mouse uterus.…”

“…Due to the fact that FOXL2 is already highly expressed in the endometrial stroma cells of the Pgr cre mice, it is difficult to distinguish the endogenous FOXL2 from the expression of the Foxl2 transgene. Since the HIS Tag epitope was incorporated into the Foxl2 transgene, the expression of the transgene in the endometrial stroma was determined by immunofluorescence staining for His tag [13]. Compared to the Pgr cre mouse uterus (Suppl.…”

“…Germline mutation in FOXL2 has been associated with the blepharophimosis-ptosis-epicanthus inversus syndrome (BPES), characterized by eyelid malformation with or without primary ovarian insufficiency in humans [8]. Similarly, Foxl2 -/mice display premature ovarian failure [9, 10].Ablation of Foxl2 at different stages of ovarian development demonstrated that Foxl2 is a major regulator for the sex differentiation and maintenance of the ovary from the embryonic stage to adulthood [11][12][13]. In the pituitary, gonadotroph specific deletion of Foxl2 in mice led to subfertility in both females and males due to Follicle-stimulating hormone (FSH) deficiency [14].…”

“…Ablation of Foxl2 at different stages of ovarian development demonstrated that Foxl2 is a major regulator for the sex differentiation and maintenance of the ovary from the embryonic stage to adulthood [11][12][13]. In the pituitary, gonadotroph specific deletion of Foxl2 in mice led to subfertility in both females and males due to Follicle-stimulating hormone (FSH) deficiency [14].…”