title: A Limited role for p21Cip1/Waf1 in maintaining normal hematopoietic stem cell functioning.
abstract: Several studies have suggested that the cyclin-dependent kinase (CDK) inhibitor p21 plays a crucial role in regulating hematopoietic stem and progenitor pool size. To allow assessment of long-term stem cell functioning in vivo, we have backcrossed a p21 null allele to C57BL/6 (B6) mice, the most commonly used mouse strain in hematopoietic stem cell research. In various in vitro assays, the homozygous deletion of the p21 allele did not affect the number of hematopoietic cells in B6 mice. Furthermore, the competitive repopulation ability was not different between p21-deficient and wild-type stem cells from both young and aged (20-month-old) mice. These results show that p21 is not essential for regulation of stem cell number in steady state. When proliferative stress was applied on p21-deficient stem cells by serial transplantation of 1,500 Lin(-)Sca-1(+)c-kit(+) (LSK) cells, again no detrimental effect was observed on cobblestone area-forming cell (CAFC) frequency and competitive repopulating ability. However, when bone marrow cells from mice that received 2 Gy of irradiation were transplanted, p21 deficiency resulted in a more than fourfold reduction in competitive repopulation index. Finally, we did not find major differences in cell cycle status and global gene expression patterns between LSK cells from p21-deficient and wild-type mice. Our findings indicate that the background of mice used for studying the function of a gene by genetic modification may determine the outcome. Cumulatively, our data fail to support the notion that p21 is essential for stem cell function during steady-state hematopoiesis, but may be relatively more important under conditions of cellular stress.
authors.affiliation: Department of Cell Biology, Section Stem Cell Biology, University Medical Center Groningen, A. Deusinglaan 1, 9713 AV Groningen, Groningen, The Netherlands. r.p.van.os@med.umcg.nl
authors.forename: Ronald
authors.initials: R
authors.lastname: van Os
authors.forename: Leonie M
authors.initials: LM
authors.lastname: Kamminga
authors.forename: Albertina
authors.initials: A
authors.lastname: Ausema
authors.forename: Leonid V
authors.initials: LV
authors.lastname: Bystrykh
authors.forename: Deanna P
authors.initials: DP
authors.lastname: Draijer
authors.forename: Kyrjon
authors.initials: K
authors.lastname: van Pelt
authors.forename: Bert
authors.initials: B
authors.lastname: Dontje
authors.forename: Gerald
authors.initials: G
authors.lastname: de Haan
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D002452:Cell Count; D002453:Cell Cycle / Q000528:radiation effects; D002455:Cell Division; D003433:Crosses, Genetic; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000166:cytology / Q000502:physiology; D005434:Flow Cytometry; D005472:Fluorouracil / Q000494:pharmacology; D018380:Hematopoietic Stem Cell Transplantation / Q000379:methods; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D018345:Mice, Knockout
chemical_list: C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D005472:Fluorouracil