In the ovaries harvested from adult rats, a strong Lgr4 immunoreactivity was detected in corpora lutea, consistent with its mRNA U0126 profile. In the testis, undifferentiated spermatogonia are discontinuously scattered around the basement of seminiferous tubules. Although Lgr4 has been Enzalutamide proposed as a stem cell marker in many tissues, our staining results showed that the Lgr4 signal is mainly located in the connected cells that form a continuous sheet surrounding the basement membrane of seminiferous tubules, suggesting that Lgr4 is unlikely to be located in spermatogonia. Real-time PCR quantification of isolated testicular cells further supported this hypothesis. Indeed, a previous study has also proposed that the Lgr4 transcript is probably expressed in the myoepithelial cells of seminiferous tubules. Using a gene trap approach, Qian et al. further demonstrated that the Lgr4 transcript is selectively located in peritubular myoid cells but not in spermatogonia of postnatal mouse testes ; these findings are consistent with our results. By disrupting the Lgr4 gene with a trap vector carrying the bgalactosidase tracing enzyme, Lgr4 in mouse ovaries has been proposed to be expressed in corpus lutea but not in other follicular compartments. Although our results of mRNA quantification and protein staining in rat ovaries indicated that corpus lutea did express the highest level of Lgr4, we also detected moderate levels of the Lgr4 transcript in other ovarian cells isolated from antral follicles. The stage difference between the appearance of Lgr4 mRNA in rat ovaries and the appearance of translated bgalactosidase protein signal in mouse ovaries may be explained by the fact that different species were used or by effects of as yet uncharacterized regulatory factors that are induced after luteogenesis to control the initiation of translation of the Lgr4 mRNA. In addition, sequence difference between endogenous Lgr4 and the tracing LacZ-containing cassette may also result in different effects on post-transcriptional or translational regulation.