Emx2 regulates mammalian reproduction by altering endometrial cell proliferation

The molecular mechanisms that underlie embryo implantation are poorly understood. Under the control of sex steroids, uterine endometrium undergoes tremendous, yet tightly controlled, proliferation in each estrous cycle to facilitate implantation; disorders of endometrial proliferation underlie several uterine diseases. We have previously identified the Emx2 gene as a transcriptional target of HOXA10 regulation in the reproductive tract. Here we report the function of Emx2 in murine implantation and regulation of endometrial proliferation. We transfected mice on d 2 post coitus with pcDNA3.1/Emx2, Emx2 antisense, or respective controls consisting of empty pcDNA3.1 or a random order oligonucleotide by intrauterine lipofection. Increased expression of Emx2 reduced average implantation rate by approximately 40% (P = 0.00006) resulting in an average number of implanted embryos per litter of 13.7 in the control group to 8.2 in the pcDNA3.1/Emx2-treated group. Neither treatment altered the number of mice attaining pregnancy with at least one embryo. Decreased Emx2 expression did not alter litter size. Neither treatment affected the birth weight of the pups. To elucidate potential mechanisms through which Emx2-regulated reproduction, markers of endometrial differentiation, proliferation, and apoptosis were assessed. Increased Emx2 expression significantly decreased endometrial cell proliferating cell nuclear antigen expression and 5'-bromo-2' deoxyuridine incorporation. Markers of stromal cell differentiation (IGF binding protein-1, prolactin), epithelial differentiation (calcitonin), and apoptosis (activated caspase3) were unchanged. In human endometrial epithelial cells in vitro, Emx2 reduced cell number indicating diminished proliferation. Emx2 controls mammalian reproduction by adjusting endometrial cell proliferation without effecting differentiation. Regulated uterine Emx2 expression is necessary during reproduction for maximal implantation and litter size.