Rossant J, Croy B A
J Embryol Exp Morphol. 1985 Apr;86:177-89.
The mouse haemochorial placenta is a complex mixture of maternal cells and foetal trophectoderm and inner cell mass (ICM)-derived cells. The majority of the placental tissue is assumed to be trophoblast in origin but the exact extent and localization of the ICM and maternal contribution has not previously been determined. Using embryo transfer and reconstituted blastocyst techniques, combined with isozymal and in situ genetic markers, we have established that about 70% of the 13 to 15-day placenta is trophectoderm-derived, 30% is maternal in origin, and 4% develops from the ICM. Nearly all of the maternal contribution was confined to the spongiotrophoblast region and all of the ICM contribution was confined to the labyrinthine trophoblast region, where it formed the foetal blood capillaries and the endodermal sinuses. Using the same genetic markers, we showed that cell suspension techniques commonly used to produce 'trophoblast' cell preparations from placenta do not enrich for trophoblast, and, indeed, that collagenase, the preferred dissociation technique for cell viability, produced cell suspensions in which ICM and maternal cells were preferentially dissociated. No method for producing pure trophoblast populations has yet been found. Some unusually high ICM contributions to the placenta were found in reconstituted blastocyst experiments using ICMs isolated from early 3.5-day blastocysts, suggesting that these ICMs may have contributed to the trophectoderm layer of the blastocyst. These and other experiments suggest that the inner cell mass lineage may not be closed until some time after formation of the blastocyst.
小鼠血绒毛膜胎盘是母细胞、胎儿滋养外胚层和内细胞团（ICM）衍生细胞的复杂混合物。大多数胎盘组织被认为起源于滋养层，但ICM和母体贡献的确切范围及定位此前尚未确定。利用胚胎移植和重构囊胚技术，结合同工酶和原位遗传标记，我们已确定，13至15天的胎盘约70%源自滋养外胚层，30%源自母体，4%由ICM发育而来。几乎所有母体贡献都局限于海绵滋养层区域，所有ICM贡献都局限于迷路滋养层区域，在该区域形成胎儿毛细血管和内胚窦。使用相同的遗传标记，我们表明，通常用于从胎盘中制备“滋养层”细胞制剂的细胞悬浮技术并不能富集滋养层，实际上，对于细胞活力而言首选的解离技术胶原酶所产生的细胞悬浮液中，ICM和母体细胞被优先解离。尚未找到产生纯滋养层细胞群体的方法。在使用从3.5天早期囊胚分离的ICM进行的重构囊胚实验中，发现一些对胎盘的ICM贡献异常高，这表明这些ICM可能对囊胚的滋养外胚层层有贡献。这些及其他实验表明，内细胞团谱系可能在囊胚形成后的一段时间内才会封闭。
