THE ETS1 TRANSCRIPTION FACTOR IS WIDELY EXPRESSED DURING MURINE EMBRYO DEVELOPMENT AND IS ASSOCIATED WITH MESODERMAL CELLS INVOLVED IN MORPHOGENETIC PROCESSES SUCH AS ORGAN FORMATION

The Ets family of genes encodes a class of transcription factors. Ets1 is predominantly expressed in the lymphoid organs of neonatal and adu lt mice, whereas Ets2 is expressed in every organ examined. In this st udy, we investigate the expression of Ets1 and Ets2 during murine embr yonic development. Our data show that Ets1 expression increases in emb ryos after implantation and during organogenesis such that it is expre ssed in all the organs of day-15 embryos studied. In later fetal stage s, Ets1 expression is predominant in the lymphoid tissues, brain, and organs that are undergoing branching morphogenesis (e.g., lung) but is dramatically reduced in other organs such as the stomach and intestin e. In neonatal development, Ets1 is expressed only in the lymphoid org ans and brain. In situ hybridization analysis demonstrates that expres sion of Ets1 occurs in mesenchymal cells of developing organs, in the nervous system, and in forming bone. Furthermore, expression of Ets1 i s upregulated in P19 cells induced to differentiate into mesoderm-like cells. Ets2, on the other hand, is expressed in differentiated and un differentiated P19 and F9 cells and in all organs of embryonic, neonat al, and adult mice studied. These data suggest that Ets1 plays an impo rtant role in mesodermal cells associated with morphogenetic processes such as organ formation and tissue modeling, whereas Ets2 plays a mor e fundamental role in cells.