Projects Catherine Robin

Objectives

Hematopoietic stem cells (HSCs) are self-renewing multipotent cells that produce all blood cell types during the entire life of an individual. Hence, they are the only cell type that can be used to replenish the bone marrow in patients with blood-related disorders. One major challenge in the field of stem cell research is to generate large quantities of these very rare cells in vitro for research and clinical use. This is extremely difficult at present because not all steps leading to HSCs generation in vivo have been elucidated yet. The overall research goal of the lab is to elucidate the cellular and molecular events leading to HSCs production and expansion during embryonic development. We notably focus on understanding the origin of HSCs during embryonic development, the mechanisms implicated in HSCs generation and expansion, the composition and function of the different HSCs niches during ontogeny, and the cellular and molecular signature of HSCs and precursors.

Figure 1.

Fig 1

Figure 1. Mouse hematopoietic development. The first hematopoietic cells appear starting at embryonic day (E)7.5 in the yolk sac, and later on also in the allantois and para-aortic splanchnopleura. The first hematopoietic stem cells (HSCs) are first detected at mid-gestation in the aorta of the aorta-gonad-mesonephros (AGM) region, and in the vitellin (VA) and umbilical arteries. They are part of intra-aortic hematopoietic clusters (IAHCs) that are tightly attached to the endothelial layer of the arteries. Later on, HSCs are also found in the yolk sac, placenta and fetal liver. In the lab we are particularly interested in unraveling the anatomical origin of the HSC potential and in understanding the molecular/cellular/mechanical events leading to HSC production.

Cellular and molecular characterization of HSCs and their precursors

All HSCs are generated during embryonic development from specialized endothelial cells endowed with a hemogenic potential. We and others have shown that hemogenic endothelial cells are present in the aorta where they generate numerous Intra-Aortic Hematopoietic Clusters (IAHCs) containing very few HSCs. Therefore, the identity of most IAHCs cells is unknown. We are interested in identifying all cell types present in IAHCs, and to elucidate at the cellular and molecular levels the successive steps leading to IAHCs and HSCs formation.

Biomechanics of HSC formation

Our research aims to uncover the essential factors that regulate embryonic HSC production. At mouse embryonic day (E)10.5, HSCs are part of IAHCs that are tightly attached to the aortic endothelium. We recently established a novel experimental imaging set-up to show the dynamic formation of HSCs directly in the aorta of the mouse embryo [1,2]. [FR2]During the endothelial into hematopoietic transition (EHT), we observed intense cellular movements and surface membrane modifications, highlighting important roles for cell adhesion molecules and microtubule (MT) cytoskeleton rearrangement. We aim to understand the basic biomechanics of embryonic HSC formation with a focus on MT regulatory proteins, which are important MT-stabilizing factors regulating cell polarity, (asymmetric) cell division, adhesion, and migration. New transgenic mouse lines will also be generated to study IAHCs formation in the mouse embryo.

Origin of HSCs

The anatomical site of mammalian HSCs origin remains controversial in mammals because the blood is already circulating at the time of HSCs detection. To solve this fundamental question, we are currently developing novel and challenging in vivo embryo rescue assay.

References

[1] Boisset JC, van Cappellen W, Andrieu-Soler C, Galjart N, Dzierzak E, Robin C (2010), In vivo imaging of haematopoietic cells emerging from the mouse aortic endothelium, Nature, 464, 116-20.
[2] Boisset JC, Andrieu-Soler C, van Cappellen WA, Clapes T, Robin C (2011), Ex vivo time-lapse confocal imaging of the mouse embryo aorta, Nat Protoc, 6, 1792-805.

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