CD34 expression by embryonic hematopoietic and endothelial cells does not require c-Myb.
CD34 is a cell-surface glycoprotein expressed in a developmental, stage-specific manner by bone marrow stem and progenitor cells. In this study we explored a possible role for c-Myb in CD34 regulation during developmental hematopoiesis. The results indicate that c-Myb can induce CD34 expression in hematopoietic and nonhematopoietic cells, and that murine CD34 promoter activity is enhanced in myeloid cells transgenic for c-Myb. To test whether c-Myb is necessary for CD34 expression during developmental hematopoiesis in vitro, c-Myb-null D3 embryonic stem (ES) cells were analyzed for their ability to develop CD34+ hematopoietic cells in vitro. CD34 promoter activity in transient transfections and CD34 upregulation during ES cell differentiation into embryoid bodies was identical in wild-type and c-Myb-null ES cells, indicating that c-Myb is not required for CD34 expression. CD34 protein is expressed on both hematopoietic and endothelial cells of the E8.5 blood islands during the development of c-Myb-null embryos, and expression is nearly identical in wild-type and c-Myb-null embryos. However, in E12.5 c-Myb-null embryos, the majority of identifiable CD34+ cells in the developing liver are endothelial rather than hematopoietic, which is consistent with the absence of colony-forming units in c-Myb-null embryos and developing ES cells. These data indicate that c-Myb is not required for CD34 expression in endothelial or primitive hematopoietic cells in the yolk sac, but is necessary for definitive hematopoiesis.
Johns Hopkins Oncology Center and Department of Gynecology and Obstetrics, Johns Hopkins University, Baltimore, Maryland, USA.
D S
DS
Krause
M L
ML
Mucenski
A M
AM
Lawler
W S
WS
May
D000818:Animals; D018952:Antigens, CD34 / Q000096:biosynthesis*; D005314:Embryonic and Fetal Development / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000276:immunology*; D006412:Hematopoietic Stem Cells / Q000276:immunology*; D051379:Mice; D009857:Oncogenes; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D015017:Yolk Sac
D018952:Antigens, CD34