CCCTC-binding factor is essential to the maintenance and quiescence of hematopoietic stem cells in mice

Hematopoiesis involves a series of lineage differentiation programs initiated in hematopoietic stem cells (HSCs) found in bone marrow (BM). To ensure lifelong hematopoiesis, various molecular mechanisms are needed to maintain the HSC pool. CCCTC-binding factor (CTCF) is a DNA-binding, zinc-finger protein that regulates the expression of its target gene by organizing higher order chromatin structures. Currently, the role of CTCF in controlling HSC homeostasis is unknown. Using a tamoxifen-inducible CTCF conditional knockout mouse system, we aimed to determine whether CTCF regulates the homeostatic maintenance of HSCs. In adult mice, acute systemic CTCF ablation led to severe BM failure and the rapid shrinkage of multiple c-Kit(hi) progenitor populations, including Sca-1⁺ HSCs. Similarly, hematopoietic system-confined CTCF depletion caused an acute loss of HSCs and highly increased mortality. Mixed BM chimeras reconstituted with supporting BM demonstrated that CTCF deficiency-mediated HSC depletion has both cell-extrinsic and cell-intrinsic effects. Although c-Kit(hi) myeloid progenitor cell populations were severely reduced after ablating Ctcf, c-Kit(int) common lymphoid progenitors and their progenies were less affected by the lack of CTCF. Whole-transcriptome microarray and cell cycle analyses indicated that CTCF deficiency results in the enhanced expression of the cell cycle-promoting program, and that CTCF-depleted HSCs express higher levels of reactive oxygen species (ROS). Importantly, in vivo treatment with an antioxidant partially rescued c-Kit(hi) cell populations and their quiescence. Altogether, our results suggest that CTCF is indispensable for maintaining adult HSC pools, likely by regulating ROS-dependent HSC quiescence.

Effect of human cytomegalovirus infection on the expression of hoxc4 and hoxc6 genes in the proliferation of lymphocytic progenitor cells / 中国实验血液学杂志

The objective of this study was to observe the expression of hoxc4 and hoxc6 genes in the process of differentiation of hematopoietic stem cell (HSC) to colony forming unit-T Lymphocyte (CFU-TL) in vitro. and to explore the possible mechanism of HCMV-induced maldevelopment of human cord blood CFU-TL on genetic level through effecting the differentiation progress by human cytomegalovirus (HCMV) with and/or all-trans retinoic acid (ATRA), Normal CFU-TL culture was used as blank control. After detection with MTT, mRNA expression levels in the human cord blood CFU-TL hoxc4 and hoxc6 genes following HCMV infection and ATRA treatment were detected by fluorogenic quantitative reserve transcription polymerize chain reaction (FQ-RT-PCR) method. HCMV of 10(6) plaque formation unit (PFU)/ml was diluted to 0.1 ml 10(5) PFU/ml and added into the infected group. The results showed that the expression of hoxc4 and hoxc6 genes in the differentiation process increased slightly on day 3, and were up to the most on day 7 (p < 0.05), while became lower on day 12 respectively in normal group, HCMV group and ATRA group. Compared with the expression of hoxc6, the expression of hoxc4 was obviously higher in each group (p < 0.05). Compared with the expression of hoxc4 and hoxc6 genes in normal group, the expressions of hoxc4 and hoxc6 in ATRA group were up-regulated remarkably (p < 0.05), while the expressions of hoxc4 and hoxc6 in group HCMV were down-regulated (p < 0.05). It is concluded that the regular expression of hoxc4 and hoxc6 genes mRNA appeared in each group. A positive co-relationship exits between hoxc4/hoxc6 genes and lymphocytic progenitor hematopoiesis. Compared with the expression of hoxc6 gene, the expression of hoxc4 gene is obviously higher in each group. HCMV can down-regulate the expression of hoxc4 and hoxc6 genes and lead to suppression effect on cell morphology, which confirms that the normal hematopoietic lineage determination and maturation rely on the stable and consistent expression of homeobox gene. At the same condition, ATRA (6 x 10(-8) mol/L at 60 nmol/ml) can up-regulate hoxc4 and hoxc6 genes expression. ATRA can up-regulate the expression of hoxc4 and hoxc6 genes.