Haploinsufficiency of AML1 results in a decrease in the number of LTR-HSCs while simultaneously inducing an increase in more mature progenitors.
The AML1/CBFbeta transcriptional complex is essential for the formation of definitive hematopoietic stem cells (HSCs). Moreover, development of the hematopoietic system is exquisitely sensitive to the level of this complex. To investigate the effect of AML1 dosage on adult hematopoiesis, we compared the hematopoietic systems of AML1+/- and AML1+/+ mice. Surprisingly, loss of a single AML1 allele resulted in a 50% reduction in long-term repopulating hematopoietic stem cells (LTR-HSCs). This decrease did not, however, extend to the next level of hematopoietic differentiation. Instead, AML1+/- mice had an increase in multilineage progenitors, an expansion that resulted in enhanced engraftment following transplantation. The expanded pool of AML1+/- progenitors remained responsive to homeostatic mechanisms and thus the number of mature cells in most lineages remained within normal limits. Two notable exceptions were a decrease in CD4(+) T cells, leading to an inversion of the CD4(+) to CD8(+) T-cell ratio and a decrease in circulating platelets. These data demonstrate a dosage-dependent role for AML1/CBFbeta in regulating the quantity of HSCs and their downstream committed progenitors, as well as a more restricted role in T cells and platelets. The latter defect mimics one of the key abnormalities in human patients with the familial platelet disorder resulting from AML1 haploinsufficiency.
Department of Pathology, St Jude Children's Research Hospital, 332 N Lauderdale St, Memphis, TN 38105, USA.
Weili
W
Sun
James R
JR
Downing
D000818:Animals; D001772:Blood Cell Count; D016026:Bone Marrow Transplantation; D018929:Cell Culture Techniques; D002454:Cell Differentiation; D019070:Cell Lineage; D002478:Cells, Cultured; D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006085:Graft Survival; D006239:Haplotypes; D006410:Hematopoiesis; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D051379:Mice; D018345:Mice, Knockout; D011518:Proto-Oncogene Proteins / Q000172:deficiency / Q000494:pharmacology*; D014157:Transcription Factors / Q000172:deficiency / Q000494:pharmacology*
D050676:Core Binding Factor Alpha 2 Subunit; D004268:DNA-Binding Proteins; D011518:Proto-Oncogene Proteins; C493726:Runx1 protein, mouse; D014157:Transcription Factors