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.
Krause
D S
DS
Johns Hopkins Oncology Center and Department of Gynecology and Obstetrics, Johns Hopkins University, Baltimore, Maryland, USA.
Mucenski
M L
ML
Lawler
A M
AM
May
W S
WS
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