Transgenic mouse analysis of Sry expression during the pre- and peri-implantation stage.

Background: The SRY/Sry gene is expressed in pre-Sertoli cells of the male genital ridge and functions as the mammalian testis determining factor (TDF). In addition, expression of SRY/Sry outside the genital ridge has been reported, including preimplantation embryos, although the functional significance of this is not well understood.

Results: Using Cre-mediated lineage studies and transgenic reporter mouse models, we now show that promoter sequences of human, pig and mouse SRY drive robust reporter gene expression in epiblast cells of peri-implantation embryos between embryonic day (E) 4.5 and E6.5. Analysis of endogenous Sry expression revealed that linear transcripts are produced by means of multiple polyadenylation sites in E4.5 embryos. Within the epiblast, SRY reporter expression mimics the expression seen using a Gata4 reporter model, but is dissimilar to that seen using an Oct4 reporter model. In addition, we report that overexpression of mouse Sry in embryonic stem cells leads to down-regulation of the core pluripotency markers Sox2 and Nanog.

Conclusion: We propose that SRY/Sry may function as a male-specific maturation factor in the peri-implantation mammalian embryo, providing a genetic mechanism to help explain the observation that male embryos are developmentally more advanced compared with female embryos, and suggesting a role for SRY beyond that of TDF.