Analysis of Runx1 Using Induced Gene Ablation Reveals Its Essential Role in Pre-liver HSC Development and Limitations of an In Vivo Approach.

Hematopoietic stem cells (HSCs) develop in the embryonic aorta-gonad-mesonephros (AGM) region and subsequently relocate to fetal liver. Runx1 transcription factor is essential for HSC development, but is largely dispensable for adult HSCs. Here, we studied tamoxifen-inducible Runx1 inactivation in vivo.

A molecular roadmap of the AGM region reveals BMPER as a novel regulator of HSC maturation.

In the developing embryo, hematopoietic stem cells (HSCs) emerge from the aorta-gonad-mesonephros (AGM) region, but the molecular regulation of this process is poorly understood. Recently, the progression from E9.5 to E10.

Understanding Hematopoietic Stem Cell Development through Functional Correlation of Their Proliferative Status with the Intra-aortic Cluster Architecture.

During development, hematopoietic stem cells (HSCs) emerge in the aorta-gonad-mesonephros (AGM) region through a process of multi-step maturation and expansion. While proliferation of adult HSCs is implicated in the balance between self-renewal and differentiation, very little is known about the proliferation status of nascent HSCs in the AGM region. Using Fucci reporter mice that enable in vivo visualization of cell-cycle status, we detect increased proliferation during pre-HSC expansion followed by a slowing down of cycling once cells start to acquire a definitive HSC state, similar to fetal liver HSCs.

Inductive interactions mediated by interplay of asymmetric signalling underlie development of adult haematopoietic stem cells.

During embryonic development, adult haematopoietic stem cells (HSCs) emerge preferentially in the ventral domain of the aorta in the aorta-gonad-mesonephros (AGM) region. Several signalling pathways such as Notch, Wnt, Shh and RA are implicated in this process, yet how these interact to regulate the emergence of HSCs has not previously been described in mammals. Using a combination of ex vivo and in vivo approaches, we report here that stage-specific reciprocal dorso-ventral inductive interactions and lateral input from the urogenital ridges are required to drive HSC development in the aorta.

Deletion of Pten in CD45-expressing cells leads to development of T-cell lymphoblastic lymphoma but not myeloid malignancies.

Since its discovery in the late 1990s, Pten has turned out to be one of the most important tumor suppressor genes. Pten loss results in increased activation of the phosphatidylinositol 3-kinase/Akt signaling pathway, which is associated with increased proliferation, survival, and neoplastic growth. Here, we have addressed the effects of conditional deletion of Pten in hematopoietic cells by crossing Pten conditional knockout mice with a knock-in mouse expressing the Cre recombinase in the CD45 locus.

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.

Transgenic tools for analysis of the haematopoietic system: knock-in CD45 reporter and deletor mice.

We have produced and characterised reporter knock-in CD45-YFP and CD45-Cre mice that drive expression of yellow fluorescent protein (YFP) and Cre-recombinase, respectively under control of the haematopoietic CD45 locus. CD45-YFP expression was characterised in various haematopoietic cells populations. The activity of CD45-Cre mice was assessed by crossing with silent GFP reporter mice.

A bovine whole-genome radiation hybrid panel and outline map.

A 3000-rad radiation hybrid panel was constructed for cattle and used to build outline RH maps for all 29 autosomes and the X and Y chromosomes. These outline maps contain about 1200 markers, most of which are anonymous microsatellite loci. Comparisons between the RH chromosome maps, other published RH maps, and linkage maps allow regions of chromosomes that are poorly mapped or that have sparse marker coverage to be identified.

A higher resolution radiation hybrid map of bovine chromosome 13.

In this paper, we present a radiation hybrid framework map of BTA13 composed of nine microsatellite loci, six genes and one EST. The map has been developed using a recently constructed 12'000 rad bovine-hamster whole-genome radiation hybrid panel. Moreover, we present a comprehensive map of BTA13 comprising 72 loci, of which 45 are microsatellites, 20 are genes and seven are ESTs.