Polycomb group gene mel-18 modulates the self-renewal activity and cell cycle status of hematopoietic stem cells.
OBJECTIVE
Mel-18 is a member of the mammalian Polycomb group (PcG) genes. This family of genes regulates global gene expression in many biologic processes, including hematopoiesis and anterior-posterior axis formation by manipulating specific target genes, including members of the Hox family. Here, we demonstrate that mel-18 negatively regulates the self-renewal activity of hematopoietic stem cells (HSCs).


METHODS
Long-term reconstitution activity was evaluated by competitive repopulating unit (CRU) and mean activity of the stem cells (MAS) assays in vivo in bone marrow cells (BMCs) derived from mel-18(-/-) and mel-18 tg mice. The expression levels of mel-18 and Hoxb4 were measured by quantitative real-time reverse transcription polymerase chain reaction.


RESULTS
The Hoxb4 gene was highly expressed in HSCs derived from mel-18(-/-) mice. The observed CRUs were 3.21, 4.77, 3.32, and 1.64 CRU per 10(5) BMCs in mel-18(+/+), mel-18(-/-), C57BL/6, and mel-18 tg, respectively. MAS was 0.58, 0.18, 0.41, and 5.89 in mel-18(+/+), mel-18(-/-), C57BL/6, and mel-18 tg, respectively. The percentage in G0 phase HSCs (lin(-)flk2(-)c-Kit(+)Sca1+ cells) was increased in mel-18(-/-) mice and decreased in mel-18 tg mice.


CONCLUSIONS
Loss or knockdown of mel-18 leads to the expression of Hoxb4, an increase in the proportion of HSCs in G0 phase, and the subsequent promotion of HSC self-renewal. These findings will enable us to develop new approaches for controlling HSC activity for hematopoietic transplantations based on ex vivo expansion of HSCs.
Kajiume
Teruyuki
T
Department of Immunology, Graduate School of Biomedical Science, Hiroshima University, Hiroshima, Japan.
Ninomiya
Yuichi
Y
Ishihara
Hiroto
H
Kanno
Rieko
R
Kanno
Masamoto
M
D000818:Animals; D001483:Base Sequence; D016026:Bone Marrow Transplantation / Q000502:physiology*; D002453:Cell Cycle / Q000502:physiology*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics*; D005801:Genes, Homeobox; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics; D007165:Immunosuppression Therapy / Q000379:methods; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D005810:Multigene Family; D063150:Polycomb Repressive Complex 1; D011754:Pyronine / Q000032:analysis; D016192:Resting Phase, Cell Cycle; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors; D014184:Transplantation, Homologous; D014916:Whole-Body Irradiation; D016335:Zinc Fingers / Q000235:genetics
D017931:DNA Primers; D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C513262:Hoxb4 protein, mouse; C066476:Pcgf6 protein, mouse; D014157:Transcription Factors; D063150:Polycomb Repressive Complex 1; D011754:Pyronine