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Fig. 4 Expression of Alk2 in Murine Hematopoietic Precursors
(A) Semiquantitative RT-PCR showing expression of Alk2 in cDNA from sorted hematopoietic precursors. Alk2 expression was detected in cDNA from hematopoietic stem cells (HSC), common myeloid progenitors (CMP) that were Flt3-positive, Pu.1-high expressing, and Pu.1-low expressing CMPs as well as in pro B cells (pro B) where two isoforms were detected. Expression was not observed in megakaryocyte-erythrocyte precursors (MEP) or in granulocyte-macrophage precursors (GMP). Primers flanked an intron and did not detect genomic DNA (gDNA). The Alk2 product is 403 bp and the GAPDH product 150 bp.
(B) Diagrammatic representation of sorted cell types during hematopoietic development. HSCs give rise to pro B cells and CMPs, while Pu.1-high CMPs are thought to differentiate as GMPs and Pu.1-low CMPs are thought to differentiate as MEPs. Alk2 is expressed in all the early precursor populations but not in the more differentiated MEP or GMP cells.
(C) Diagrammatic representation of the genetic pathways regulating the transition between the hemangioblast (dark gray) and myeloid precursor (light gray) cellular states in the zebrafish ALPM. Events occurring between bud and 4-somite stages are shown in black.