Hisami Shiraishi

Decidua as a Site of Extrathymic VγI T-cell Differentiation

PROBLEM: Decidual tissue is an interface between the host and fetus, which is regarded as a natural allograft. We have reported the possible presence of extrathymic T cells in human decidua through the expression of recombinase‐activating genes in the decidual CD16− CD56bright large granular lymphocytes.

Expression of the recombinase-activating gene (RAG-1) in murine early embryogenesis

The recombinase activation genes, RAG‐1 and RAG‐2, are expressed together in immature T or B lymphocytes and possess activity to induce V(D)J rearrangement in T cell receptor (TCR) and Ig genes. In vertebrates, only Ig and TCR molecules are reported to have recombination in their development using multiple V, D, J component gene segments. Thus, expression of RAG genes are localized only in lymphoid organs and sites of extrathymic T cell differentiation. In this study, we have used RAG‐1 and RAG‐2 genes as markers of possible genetic recombination in developing murine preimplanation embryos, using the highly sensitive reverse transcriptase polymerase chain reaction (RT‐PCR) technique and in situ hybridization. From 40 preimplantation embryos of various developmental stages we extracted RNA. reverse‐transcribed it into cDNA and used it in RT‐PCR studies. A PCR of 35 cycles disclosed expression of RAG‐1 but not RAG‐2 in morulae and blastocysts. Southern blot hybridization using a specific synthetic oligonucleotide probe for RAG‐1 and RT‐PCR with another primer pair identified RAG‐1 expression in developing embryos. In situ hybridization using a cooled CCD camera also revealed localization of RAG‐1 mRNA in blastocysts. We propose possible genetic recombination during late preimplantation murine embryogenesis which may contribute to the loss of totipotency and differentiation of inner cell mass and trophoectoderm.