Rex Hess

Estrogen actions are mediated by both nuclear (n) and membrane (m) localized estrogen receptor 1 (ESR1). Male Esr1 knockout (Esr1KO) mice lacking functional Esr1 are infertile, with reproductive tract abnormalities. Male mice expressing nESR1 but lacking mESR1 (nuclear-only estrogen receptor 1 mice) are progressively infertile due to testicular, rete testis, and efferent ductule abnormalities similar to Esr1KO males, indicating a role for mESR1 in male reproduction. The H2NES mouse expresses only mESR1 but lacks nESR1. The goal of this study was to identify the functions of mESR1 alone in mice where nESR1 was absent. Breeding trials showed that H2NES males are fertile, with decreased litter numbers but normal pup numbers/litter. In contrast to Esr1KO mice, H2NES testicular, and epididymal weights were not reduced, and seminiferous tubule abnormalities were less pronounced. However, Esr1KO and H2NES males both had decreased sperm motility and a high incidence of abnormal sperm morphology. Seminiferous tubule and rete testis dilation and decreased efferent ductule epithelial height characteristic of Esr1KO males were reduced in H2NES. Consistent with this, expression of genes involved in fluid transport and ion movement that were reduced in Esr1KO (Aqp1, Car2, Car14, Cftr) were partially or fully restored to wild-type levels in H2NES. In summary, in contrast to Esr1KO males, H2NES males are fertile and have reduced phenotypic and functional abnormalities in the testis and efferent ductules. Thus, mESR1 alone, in the absence of nESR1, can partially regulate male reproductive tract structure and function, emphasizing its importance for overall estrogen action.