Heterogeneity in sexual bipotentiality and plasticity of granulosa cells in developing mouse ovaries

Abstract

SummaryIn mammalian sex determination, SRY directly upregulates the expression of SOX9, the master regulatory transcription factor in Sertoli cell differentiation, leading to testis formation. Without SRY action, the bipotential gonadal cells become pre-granulosa cells, which results in ovarian follicle development. When, where and how pre-granulosa cells are determined to differentiate into developing ovaries, however, remains unclear. By monitoring SRY-dependent SOX9 inducibility (SDSI) in an Sry-inducible mouse system, we were able to identify spatiotemporal changes in the sexual bipotentiality/plasticity of ovarian somatic cells throughout life. The early pre-granulosa cells maintain the SDSI until 11.5 d.p.c., after which most pre-granulosa cells rapidly lose this ability by 12.0 d.p.c. Unexpectedly, we found a subpopulation of the pre-granulosa cells near the mesonephric tissue that continuously retains SDSI throughout fetal and early postnatal stages. After birth, these SDSI-positive pre-granulosa cells contribute to the initial round of folliculogenesis by the secondary follicle stage. In experimental sex reversal of 13.5-d.p.c. ovaries grafted into adult male nude mice, the differentiated granulosa cells re-acquire the SDSI before other signs of masculinization. Our data provide direct evidence of an unexpectedly high sexual heterogeneity of granulosa cells in developing mouse ovaries in a stage-and region-specific manner. Discovery of such sexually bipotential granulosa cells provides a novel entry point to the understanding of masculinization in various cases of XX disorders of sexual development in mammalian ovaries.

From Sex Determination to Initial Folliculogenesis in Mammalian Ovaries: Morphogenetic Waves along the Anteroposterior and Dorsoventral Axes

“…In mouse XX gonads, FOXL2 expression is first detectable in several gonadal somatic cells located at the anterior mesonephric (anterior-dorsal) side at around E12.0, after which its expression domain rapidly expands toward the coelomic epithelial (ventral) side in addition to the anterior and posterior poles by E12.5 [see fig. S3 in Harikae et al, 2013b]. After E12.5, most of the FOXL2-positive cells reside along the mesonephros, whereas only few are within the coelomic domain [Mork et al, 2012], similar to other genes that display a gradient pattern of ovary-specific expression (e.g.…”

“…amined throughout the embryonic and peri-and postnatal stages [Harikae et al, 2013b]. XX pre-granulosa cell precursors maintained the SDSI until E11.5, after which most pre-granulosa cells rapidly lost this ability in an anterior-to-posterior manner by E12.0.…”

“…The earliest cellular event in developing ovaries is the loss of SRY-dependent SOX9-inducibility (SDSI) in XX gonadal supporting cells in an anterior-to-posterior wave-like manner from E11.5 to E12.0 [Hiramatsu et al, 2009;Harikae et al, 2013b]. We have previously shown that forced ubiquitous SRY activation throughout the entire region of developing XX gonads at early stages ( ∼ E10.0) led to the formation of an XX testis with a normal spatiotemporal SOX9 expression profile, in which the gonadal supporting cells did not show any advance in timing or ectopic activation of Sox9 initiation Kidokoro et al, 2005].…”

“…The feminizing signals of WNT4, RA and FOXL2 appear to antagonize the intrinsic DMRT1 action in differentiating XX gonads by E13.5 [ fig. S10 in Harikae et al, 2013b], but are competed against and repressed by a center-to-pole masculinizing wave of SRY-dependent SOX9-FGF9 positive-feedback signals in developing XY gonads. The dynamic waves of ovarian differentiation are shown schematically in figure 3 .…”

Building an Ovary: Insights into Establishment of Somatic Cell Lineages in the Mouse

“…These data suggest that at least 2 different FOXL2-positive populations exist within the fetal ovary: one expressing Foxl2 in an Rspo1 -dependent manner under the surface epithelium, and the other population expressing Foxl2 independent of Rspo1 close to the mesonephros. Heterogeneity within granulosa cells population was further brought to light by Harikae et al [2013]. They identified a subpopulation of pre-granulosa cells that continuously retains an 'SRY-dependent SOX9-inducibility' (SDSI) throughout fetal and early postnatal stages whereas this ability should be lost by E12.5.…”