Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/33361
Title: CHARACTERIZATION OF HEMATOPOIETIC STEM CELL NICHES IN THE EARLY STAGE MOUSE EMBRYOS
Authors: LIU YACHAO
Keywords: hematopoietic stem cells, growth factors, yolk sac endoderm, midkine
Issue Date: 16-Jan-2012
Source: LIU YACHAO (2012-01-16). CHARACTERIZATION OF HEMATOPOIETIC STEM CELL NICHES IN THE EARLY STAGE MOUSE EMBRYOS. ScholarBank@NUS Repository.
Abstract: During mouse development, hematopoietic stem cells (HSCs) have been identified in the yolk sac (YS), aorta-gonado-mesonephros (AGM) region, placenta and fetal liver. In an effort to understand how the embryonic microenvironments that HSCs encounter influence their proliferation and maintenance we performed a comparative qPCR analysis at different time points between the YS, AGM, placenta and fetal liver. We were interested in the expression pattern of angiopoietin-like protein 3 (Angptl3), insulin-like growth factor 2 (IGF2), stem cell factor (SCF) and thrombopoietin (TPO) and whether these factor could be a signature for a stromal cell. This combination of growth factors has been shown to support proliferation of HSCs in a serum-free ex vivo culture system. Intriguingly, we found that the YS expressed higher levels of these known HSC supportive growth factors compared to the AGM and placenta but comparable levels to the fetal liver. Thus we hypothesize that potential HSCs-supportive stromal cells might exist in the YS, and we then carried out the research to identify and characterize those stromal cells. So far, we were able to show that the population of cells from day 10.5 pc YS that expressed HSC-supportive growth factors are large in size, have high granularity and express intermediate levels of Delta-like-1 (Dlk-1), a marker for a recently reported type of fetal liver stromal cell for HSCs. We determined that this population of cells is of the endoderm lineage, as evidenced by their specific expression of endoderm markers. To examine the function of the YS endoderm cells, we cocultured these cells with bone marrow cells in vitro, and the results showed that YS endoderm cells support great proliferation of bone marrow derived hematopoietic cells. Moreover, cell-cell contact is needed to keep the enriched HSC population, i.e. lineage-Sca-1+c-Kit+ cells, undifferentiated. In addition, we also performed genome-wise analysis of the gene expression of the endoderm cells, and we particularly focused on the growth factor expression pattern. So far we have identified a novel growth factor, midkine, for supporting HSCs during ex vivo culture. Through long-term transplantation assay, we have shown that addition of midkine at an intermediate concentration will facilitate maintenance of the HSCs up to 4 days. Our finding suggests that primary extraembryonic endoderm cells may serve as hematopoietic progenitor cell supportive stromal cells. Novel growth factors expressed by the yolk sac endoderm cells may be utilized to optimize current protocol for ex vivo culture of HSCs.
URI: http://scholarbank.nus.edu.sg/handle/10635/33361
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