Primitive @entity1 hematopoietic precursors express XXXX but not @entity588 .

@entity1 @entity588 @entity1836 @entity3053 @entity2280
@entity588 and its homologue, @entity1836 , encode membrane-associated proteins that suppress programmed cell death of hematopoietic cell lines after growth factor withdrawal, and are expressed in hematopoietic precursor cells. To better understand the maintenance of long-term survival in the hematopoietic stem cell population, we evaluated the expression patterns of @entity588 and @entity1836 in primitive hematopoietic precursor populations. Hematopoietic precursor cells expressing @entity2280 ( @entity2280 +) and lacking maturation-linked surface antigens (lin-) were isolated from adult @entity1 bone marrow using two-color immunofluorescence cell sorting and fractionated on the basis of forward light scatter characteristics into blast-sized and small to medium lymphocyte-sized cell populations. @entity588 expression was shown in 78% to 90% of @entity2280 + lin- blast-sized cells versus less than 10% of small to medium lymphocyte-sized @entity2280 + lin- cells by immunohistochemical analysis. Small to medium lymphocyte-sized @entity2280 + lin- cells were further enriched for primitive precursors by selecting cells that lacked expression of @entity3053 ( @entity2280 + lin- @entity3053 -). In parallel experiments, only 1% to 4% of @entity2280 + lin- @entity3053 - cells expressed @entity588 , whereas 45% to 56% of these cells generated colony-forming cells. In contrast, > or = 94% of cells in all bone marrow subpopulations studied expressed @entity1836 protein. Both alternatively spliced @entity1836 transcripts, @entity1836 and bcl-xs, were present. Our data show that the most primitive hematopoietic precursors express @entity1836 but not @entity588 . Thus, the functional @entity588 homologue, @entity1836 , may be essential for the long-term survival of the hematopoietic stem cell population.
