Characterization of Toll- Like Receptor 9 expression during Mouse Preimplantation

Toll-like receptor9 ( TLR9) is a pathogenic sensing receptor that binds to various pathogenic components, recognizing foreign genomic DNA. Numerous studies have reported the functions of TLR9in somatic cells, but its feature in germ cells and early embryos has not been well understood. In this study, to characterize TLR9during preimplantation development, we investigated the mRNA and protein expression dynamics of TLR9in mouse oocytes and embryos. Gene expression analysis revealed the presence of Tlr9transcripts 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 lineagesof embryonic and trophoblaststem cells, and found that both undifferentiated and differentiated trophoblaststem cells expressed Tlr9mRNA, while embryonic stem cellsdid not. These results highlight the dynamics of the TLR9localization pattern and suggest its potential participation in mouse embryo development.