The development of the embryonic hemopoietic organs from yolk sac to liver and spleen: a cytometrical observation.

我们这两年的研究得出了以下结果。(1)卵黄囊造血和卵黄囊循环红母细胞的起源小鼠胚胎卵黄囊的造血在妊娠第8天开始，卵黄蛋白血管形成后，红细胞在第10天开始活跃。造血病灶包含不同发育阶段的原始红母细胞，其中存在少量细胞核直径超过8微米的大的未成熟造血细胞。这种未成熟的造血细胞类似于晚期成血管细胞，存在于10天胚胎的外周循环中。(2)肝造血和脾造血在妊娠第11天，肝组织中含有未成熟的造血细胞，其细胞核和核仁的外观类似于晚期成血管细胞。这种造血细胞的核直径大于8um，在妊娠15天前可以在肝脏中看到。脾索内出现未成熟的造血细胞，出生后2天仍可在脾内看到。(3)脾脏造血和淋巴细胞妊娠第16天，首先出现未成熟的造血细胞和小淋巴细胞，随后脾脏以红细胞为主。骨髓采血前胎儿脾脏可能是b淋巴细胞群的来源。(4)巨核生成卵黄囊卵黄血管中含有少量游离的巨核生成细胞。卵黄囊巨核细胞的细胞大小明显小于骨髓巨核细胞，可分为YM1、YM2和YM3三种类型。大多数11天胚胎的肝巨核细胞具有与YM1或YM2细胞相似的超微结构特征。

Our study of these two years gave the following results.(1) Yolk sac hemopoiesis and circulating erythroblasts of yolk sac originHemopoiesis in the yolk sac of the mouse embryo begins at 8 days of gestation, after the formation of vitellin vessels, erythtopoiesis appears to be active at 10 days. The hemopoietic foci contain primitive erythroblasts of various stages of development, and among them there exist small number of large, immature, hemopoietic cells with nuclei over 8 um in diameter. Such immature hemopoietic cells resembling late angioblasts are present in the peripheral circulation of a 10-day embryo.(2)Liver hemopoiesis and spleen hemopoiesisAt 11 days of gestation, hepatic tissues contain immature hemopoietic cells which resemble late angioblasts on the basis of their nuclear and nucleolar appearance. Such hemopoietic cells measure larger than 8 um nuclear diameter and can be seen in the liver unitl 15 days of gestation. Then the immature hemopoietic cells appear in the splenic cords, and the cells can be seen in the spleen even at 2 days after birth.(3)Spleen hemopoiesis and lymphocytesAt 16 days of gestation, immature hemopoietic cells and small lymphocytes first appear and then the spleen become predominantly erythroietic. The fetal spleen is the possible source of B-lymphocyte population before the bone marrow hemopiesis.(4)MegakaryopoiesisYolk sac vitelline vessels contain a few free megakaryopoietic cells. Yolk sac megakaryopoietic cells, which are significantly smaller in cell size than bone marrow megakaryopoietic cells, can be classified into three types: YM1, YM2, and YM3. Most of the hepatic megakaryopoietic cells of an 11-day embryo have ultrastructural features similar to those of YM1 or YM2 cells.