title: Determining c-Myb protein levels can isolate functional hematopoietic stem cell subtypes.
abstract: The transcription factor c-Myb was originally identified as a transforming oncoprotein encoded by two avian leukemia viruses. Subsequently, through the generation of mouse models that affect its expression, c-Myb has been shown to be a key regulator of hematopoiesis, including having critical roles in hematopoietic stem cells (HSCs). The precise function of c-Myb in HSCs although remains unclear. We have generated a novel c-myb allele in mice that allows direct observation of c-Myb protein levels in single cells. Using this reporter line we demonstrate that subtypes of HSCs can be isolated based upon their respective c-Myb protein expression levels. HSCs expressing low levels of c-Myb protein (c-Myb(low) HSC) appear to represent the most immature, dormant HSCs and they are a predominant component of HSCs that retain bromodeoxyuridine labeling. Hematopoietic stress, induced by 5-fluorouracil ablation, revealed that in this circumstance c-Myb-expressing cells become critical for multilineage repopulation. The discrimination of HSC subpopulations based on c-Myb protein levels is not reflected in the levels of c-myb mRNA, there being no more than a 1.3-fold difference comparing c-Myb(low) and c-Myb(high) HSCs. This illustrates how essential it is to include protein studies when aiming to understand the regulatory networks that control stem cell behavior.
authors.affiliation: Department of Cell Differentiation, Institute of Molecular Embryology and Genetics, Kumamoto City, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sakamoto
authors.forename: Naoki
authors.initials: N
authors.lastname: Takeda
authors.forename: Fumio
authors.initials: F
authors.lastname: Arai
authors.forename: Kentaro
authors.initials: K
authors.lastname: Hosokawa
authors.forename: Paloma
authors.initials: P
authors.lastname: Garcia
authors.forename: Toshio
authors.initials: T
authors.lastname: Suda
authors.forename: Jon
authors.initials: J
authors.lastname: Frampton
authors.forename: Minetaro
authors.initials: M
authors.lastname: Ogawa
mesh_terms: D000818:Animals; D005786:Gene Expression Regulation / Q000502:physiology*; D017930:Genes, Reporter; D006410:Hematopoiesis / Q000502:physiology*; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism*; D051379:Mice; D020598:Proto-Oncogene Proteins c-myb / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D020598:Proto-Oncogene Proteins c-myb
keywords: Animals; Cell proliferation; Genetically modified; Hematopoiesis; Hematopoietic stem cell transplantation; Hematopoietic stem cells; Proto-oncogene proteins c-myb