The homeodomain gene Pitx2 is expressed in primitive hematopoietic stem/progenitor cells but not in their differentiated progeny

Objective. Hematopoietic stem cells (HSCs) represent a rare and incompletel y characterized fraction of marrow cells that are capable of both self-rene wal and differentiation into all of the mature cells in the peripheral bloo d, We undertook to identify genes expressed preferentially by HSCs as an in itial step toward better understanding the molecular mechanisms that underl ie HSC behavior. Methods, We modified the representational difference analysis technique to isolate gene fragments present in amplified cDNA prepared from highly purif ied murine hematopoietic stem/ progenitor cells (Lin(-)/Hoechest(low)/rhoda mine(low)) and absent (or much less abundant) in amplified cDNA prepared fr om lineage-committed marrow cells. We went on to use one potentially import ant gene fragment that we isolated in this way, to screen a cDNA library pr epared from these cells and to characterize the pattern of expression of th e gene in hematopoietic and other cells. Results. We isolated a fragment of the homeobox transcription factor Pitx2, from amplified cDNA prepared from murine hematopoietic stem/progenitor cel ls. From a cDNA library prepared from these cells, a full-length cDNA was i solated that corresponds to one of the three known isoforms of Pitx2 (Pitx2 c), Pitx2c is expressed in murine embryonic stem (ES) cells and in hematopo ietic stem/progenitor cells but not in more differentiated hematopoietic ce lls or in a large panel of established murine hematopoietic cell lines. Pit x2c expression was not detected after 48 hours of in vitro cytokine stimula tion of hematopoietic stem/progenitor cells, Conclusions. Pitx2c is expressed in hematopoietic stem/progenitor cells but not in their differentiated progeny. The pattern of expression of Pitx2c i n primitive hematopoietic stem/progenitor cells suggests that it may play a role in hematopoietic stem-cell biology. (C) 2001 International Society fo r Experimental Hematology. Published by Elsevier Science Inc.