Involvement of transcription factors TCF-1 and GATA-3 in the initiation of the earliest step of T cell development in the thymus

Flow cytometric and imnunocytochemical analyses of murine fetal thymus (FT) cells with antibodies to various surface markers and transcription factors reveal that the synthesis of TCF-1 and GATA-3 proteins begins simultaneously in a fraction of the most immature population of FT cells, which have the phenotype of CD4^-CD8^-CD44⁺CD25 . No TCF-1-producing cell is found in the fetal liver (FL). In CD44⁺CD25^- FT cells, the production of TCF-1 is immediately followed by intracellular expression of CD3ε. It is also found that the T cell development from FL, but not FT, progenitors in the FT organ culture system is severely inhibited by the addition of antisense oligonucleotides for either TCF-1 or GATA-3. These results strongly suggest that TCF-1 and GATA-3 play essential roles in the initiation of the earliest steps oft cell development in the thymus.