Blood cells are constantly produced in the bone marrow (BM) of adult mammals. This constant turnover ultimately depends on a rare population of progenitors that displays self-renewal and multilineage differentiation potential, the hematopoietic stem cells (HSCs). It is generally accepted that HSCs are generated during embryonic development and sequentially colonize the fetal liver, the spleen, and finally the BM. Here we discuss the experimental evidence that argues for the extrinsic origin of HSCs and the potential locations where HSC generation might occur. The identification of the cellular components playing a role in the generation process, in these precise locations, will be important in understanding the molecular mechanisms involved in HSC production from undifferentiated mesoderm.

中文翻译：

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造血系统的个体发育。

成年哺乳动物的骨髓（BM）中不断产生血细胞。这种恒定的周转率最终取决于具有自我更新和多系分化潜能的罕见祖细胞，即造血干细胞（HSC）。公认的是，HSCs是在胚胎发育过程中产生的，并随后定居在胎儿肝脏，脾脏，最后是BM。在这里，我们讨论了实验证据，这些证据证明了造血干细胞的外在起源和可能发生造血干细胞的潜在位置。在这些精确的位置鉴定在生成过程中起重要作用的细胞成分，对于理解由未分化的中胚层产生HSC的分子机制至关重要。