Characterization of Toll- Like Receptor 9 expression during Mouse Preimplantation

Toll-like receptor 9 (TLR9) is a pathogenic sensing receptor that binds to various pathogenic components, recognizing foreign genomic DNA. Numerous studies have reported the functions of TLR9 in somatic cells, but its feature in germ cells and early embryos has not been well understood. In this study, to characterize TLR9 during preimplantation development, we investigated the mRNA and protein expression dynamics of TLR9 in mouse oocytes and embryos. Gene expression analysis revealed the presence of Tlr9 transcripts except during the morula stage. Subsequent immunofluorescence revealed trophectoderm- predominant localization during the blastocyst stage. We next assessed whether the predominance was common in different cell lineages of embryonic and trophoblast stem cells, and found that both undifferentiated and differentiated trophoblast stem cells expressed Tlr9 mRNA, while embryonic stem cells did not. These results highlight the dynamics of the TLR9 localization pattern and suggest its potential participation in mouse embryo development.