Hoxb4-YFP reporter mouse model: a novel tool for tracking HSC development and studying the role of Hoxb4 in hematopoiesis.

Hoxb4 overexpression promotes dramatic expansion of bone marrow (BM) hematopoietic stem cells (HSCs) without leukemic transformation and induces development of definitive HSCs from early embryonic yolk sac and differentiating embryonic stem cells. Knockout studies of Hoxb4 showed little effect on hematopoiesis, but interpretation of these results is obscured by the lack of direct evidence that Hoxb4 is expressed in HSCs and possible compensatory effects of other (Hox) genes. To evaluate accurately the pattern of Hoxb4 expression and to gain a better understanding of the physiologic role of Hoxb4 in the hemato-poietic system, we generated a knock-in Hoxb4-yellow fluorescent protein (YFP) reporter mouse model.

Restoration of Runx1 expression in the Tie2 cell compartment rescues definitive hematopoietic stem cells and extends life of Runx1 knockout animals until birth.

Mice deficient in the runt homology domain transcription factor Runx1/AML1 fail to generate functional clonogenic hematopoietic cells and die in utero by embryonic day 12.5. We previously generated Runx1 reversible knockout mice, in which the Runx1 locus can be restored by Cre-mediated recombination.

The differentiation program of embryonic definitive hematopoietic stem cells is largely alpha4 integrin independent.

Previous analyses of the roles of alpha4 integrins in hematopoiesis by other groups have led to conflicting evidence. alpha4 integrin mutant cells developing in [alpha4 integrin(-/-): wt] chimeric mice are not capable of completing lymphomyeloid differentiation, whereas conditional inactivation of alpha4 integrin in adult mice has only subtle effects. We show here that circumventing the fetal stage of hematopoietic stem cell (HSC) development by transplantation of embryonic alpha4 integrin(-/-) cells into the adult microenvironment results in robust and stable long-term generation of alpha4 integrin(-/-) lymphoid and myeloid cells, although colonization of Peyer patches and the peritoneal cavity is significantly impaired.

Progressive divergence of definitive haematopoietic stem cells from the endothelial compartment does not depend on contact with the foetal liver.

The yolk sac and the para-aortic splanchnopleura/aorta-genital ridges-mesonephros (P-Sp/AGM) region are the main sites of haematopoietic activity in the mouse embryo at the pre-liver stage of development. By day 11.5 of gestation, the AGM region is capable of autonomous initiation and expansion of definitive haematopoietic stem cells (HSCs).

Thioredoxin-related regulation of NO/NOS activities.

The role of regulation of nitric oxide synthase (NOS) activity in mitigating oxidative stress in neonatal lungs and contributing to pulmonary vasodilation at birth is still unclear. Furthermore, it is known that, depending on interactions between the individual components of the mitogen-activated protein kinase (MAPK) signaling cascades, many biological consequences, including apoptosis, are initiated. Although the importance of nitric oxide (NO) in apoptosis is controversial and likely depends on NO concentrations and cell types, this highly reactive free radical can activate the p38 MAPK signal cascade.