Reduced proliferative capacity of hematopoietic stem cells deficient in Hoxb3 and Hoxb4.
Several homeobox transcription factors, such as HOXB3 and HOXB4, have been implicated in regulation of hematopoiesis. In support of this, studies show that overexpression of HOXB4 strongly enhances hematopoietic stem cell regeneration. Here we find that mice deficient in both Hoxb3 and Hoxb4 have defects in endogenous hematopoiesis with reduced cellularity in hematopoietic organs and diminished number of hematopoietic progenitors without perturbing lineage commitment. Analysis of embryonic day 14.5 fetal livers revealed a significant reduction in the hematopoietic stem cell pool, suggesting that the reduction in cellularity observed postnatally is due to insufficient expansion during fetal development. Primitive Lin(-) ScaI(+) c-kit(+) hematopoietic progenitors lacking Hoxb3 and Hoxb4 displayed impaired proliferative capacity in vitro. Similarly, in vivo repopulating studies of Hoxb3/Hoxb4-deficient hematopoietic cells resulted in lower repopulating capability compared to normal littermates. Since no defects in homing were observed, these results suggest a slower regeneration of mutant HSC. Furthermore, treatment with cytostatic drugs demonstrated slower cell cycle kinetics of hematopoietic stem cells deficient in Hoxb3 and Hoxb4, resulting in increased tolerance to antimitotic drugs. Collectively, these data suggest a direct physiological role of Hoxb4 and Hoxb3 in regulating stem cell regeneration and that these genes are required for maximal proliferative response.
Department of Molecular Medicine and Gene Therapy, Lund University Hospital, Lund, Sweden.
Jon Mar
JM
Björnsson
Nina
N
Larsson
Ann C M
AC
Brun
Mattias
M
Magnusson
Elisabet
E
Andersson
Patrik
P
Lundström
Jonas
J
Larsson
Ewa
E
Repetowska
Mats
M
Ehinger
R Keith
RK
Humphries
Stefan
S
Karlsson
D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D016026:Bone Marrow Transplantation; D002455:Cell Division / Q000502:physiology*; D005472:Fluorouracil / Q000494:pharmacology; D018390:Gene Targeting; D006410:Hematopoiesis / Q000502:physiology; D006412:Hematopoietic Stem Cells / Q000187:drug effects / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*
D000963:Antimetabolites; D018398:Homeodomain Proteins; C078105:Hox 2.7 protein, Xenopus; C513262:Hoxb4 protein, mouse; D014157:Transcription Factors; D029867:Xenopus Proteins; D005472:Fluorouracil