Iroquois function in the female reproductive tract

Project summary/Abstract Two existential threats to female fertility include the premature loss of the ovarian reserve and early implantation/placentation failure. We recently discovered that Irx3 and Irx5, two of six members of the Iroquois homeobox (Irx) transcription factor family, show remarkable conservation of molecular and cellular actions associated with cognate cell-cell transitions critical for germline nest breakdown and primordial follicle formation (ovarian reserve) during ovary development and embryo-endometrial interactions leading to vasculogenesis during implantation and establishment of pregnancy. Previously, we employed a series of Irx3/5 mutant mouse models, including an Sf1-Cre/Flox strategy to highlight autonomous roles for Irx3 vs Irx5, especially in somatic cells. The fertility profiles for these mice also indicated that developmental expression of Irx3 contributes to the adult follicle’s response to external growth and ovulation signals and suggested that Irx3 has a critical role in oocyte integrity. AIM 1 is designed to discover the roles for Irx3 in the oocyte and uncover downstream targets and regulation profiles over time in ovary development. Ovarian histology and follicle counts identified oocyte deficits, but reproductive data suggested that other factors were also contributing to the subfertility phenotype in Irx3 knockout mice (Irx3 KO). Indeed, ablation of Irx3 in female mice resulted in a subfertile phenotype with fewer pups born in each litter. Our studies indicated a marked induction of Irx3 at the onset of decidualization and we observed a progressive loss of embryos starting at the decidual phase and extending through the end of pregnancy indicating a disrupted uterine response to the embryo that caused deficits in placentation. AIM 2 will test the hypothesis that Irx3 integrates stromal-endothelium and stromal-trophoblast interactions to ensure successful establishment of pregnancy. Finally, we observed punctate staining for IRX3 within cytoplasm of oocytes and uterine decidual cells. Based on our observations that IRX3 plays an important role in mediating cell-cell interactions, AIM 3 is designed to examine cytoplasmic signaling and localization of cytoskeletal machinery with respect to IRX3 presence. Altogether, our studies are designed to discover how Iroquois homeobox proteins mediate germline nest breakdown and primordial follicle formation to establish responsive follicles with healthy oocytes and decidualization that promotes a successful implantation and placentation program. Successful outcomes will increase our understanding of the biology that results in a healthy ovarian reserve and optimal uterine conditions for early embryo survival.