在胚胎发育过程中血液的形成(造血作用)有两个已经得到承认的阶段：一个是最初的“原始”阶段，发生在胚胎外卵黄囊中，向早期胚胎提供营养；另一个是“最后”阶段，开始于胚胎中一个被称为“大动脉-性腺-中肾”的区域。关于最后造血细胞群的来源是局部的还是外部的(即由从卵黄囊中向内迁移的前体细胞衍生而来)长期存在争论。一项新的非入侵性细胞跟踪研究与当前的正统观点产生抵触，该研究结果表明，卵黄囊的确是成年造血干细胞的来源。关于血液供应起源的知识，也许对在培养中生成血液干细胞的研究工作有意义，并且还有可能用于治疗工作。
英文原文:
Nature 446, 1056-1061 (26 April 2007) | doi:10.1038/nature05725; Received 15 June 2006; Accepted 2 March 2007; Published online 21 March 2007
Cell tracing shows the contribution of the yolk sac to adult haematopoiesis
Igor M. Samokhvalov1, Natalia I. Samokhvalova1 & Shin-ichi Nishikawa1
- Laboratory for Stem Cell Biology, Center for Developmental Biology, RIKEN Kobe, Kobe 650-0047, Japan
Correspondence to: Igor M. Samokhvalov1 Correspondence and requests for materials should be addressed to I.M.S. (Email: igors@cdb.riken.jp).
The first haematopoietic stem cells (HSCs) appear in the aorta-gonad-mesonephros (AGM) region, major vitelline and umbilical vessels, and placenta; however, whether they arise locally or from immigrant yolk sac precursor cells remains unclear. This issue is best addressed by measuring cell-lineage relationships rather than cell potentials. To undertake long-term in vivo tracing of yolk sac cells, we designed a non-invasive pulse-labelling system based on Cre/loxP recombination. Here we show that in Runx1+/- (runt-related transcription factor 1) heterozygous mice, yolk sac cells expressing Runx1 at embryonic day 7.5 develop into fetal lymphoid progenitors and adult HSCs. During mid-gestation the labelled (embryonic day 7.5) yolk sac cells colonize the umbilical cord, the AGM region and subsequently the embryonic liver. This raises the possibility that some HSCs associated with major embryonic vasculature are derived from yolk sac precursors. We observed virtually no contribution of the labelled cells towards the yolk sac vasculature, indicating early segregation of endothelial and haematopoietic lineages.
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