Parameswaran M, Tam P P
Embryology Unit, Children's Medical Research Institute, Wentworthville, Australia.
Dev Genet. 1995;17(1):16-28. doi: 10.1002/dvg.1020170104.
The developmental fate of cells in the epiblast of early-primitive-streak-stage mouse embryos was assessed by studying the pattern of tissue colonisation displayed by lac Z-expressing cells grafted orthotopically to nontransgenic embryos. Results of these fate-mapping experiments revealed that the lateral and posterior epiblast contain cells that will give rise predominantly to mesodermal derivatives. The various mesodermal populations are distributed in overlapping domains in the lateral and posterior epiblast, with the embryonic mesoderm such as heart, lateral, and paraxial mesoderm occupying a more distal position than the extraembryonic mesoderm. Heterotopic grafting of presumptive mesodermal cells results in the grafted cells adopting the fate appropriate to the new site, reflecting a plasticity of cell fate determination before ingression. The first wave of epiblast cells that ingress through the primitive streak are those giving rise to extraembryonic mesoderm. Cells that will form the mesoderm of the yolk sac and the amnion make up a major part of the mesodermal layer of the midprimitive-streak-stage embryo. Cells that are destined for embryonic mesoderm are still found within the epiblast, but some have been recruited to the distal portion of the mesoderm. By the late-primitive-streak-stage, the mesodermal layer contains only the precursors of embryonic mesoderm. This suggests that there has been a progressive displacement of the midstreak mesoderm to extraembryonic sites, which is reminiscent of that occurring in the overlying endodermal tissue. The regionalisation of cell fate in the late-primitive-streak mesoderm bears the same spatial relationship as their ancestors in the epiblast prior to cell ingression. This implies that both the position of the cells in the proximal-distal axis and their proximity to the primitive streak are major determinants for the patterning of the embryonic mesoderm.
通过研究原位移植到非转基因胚胎的表达lac Z的细胞所显示的组织定植模式，评估了早期原条期小鼠胚胎上胚层细胞的发育命运。这些命运图谱实验的结果表明，外侧和后部上胚层包含主要产生中胚层衍生物的细胞。各种中胚层群体分布在外侧和后部上胚层的重叠区域，胚胎中胚层如心脏、外侧和轴旁中胚层比胚外中胚层占据更靠远端的位置。假定中胚层细胞的异位移植导致移植细胞采用适合新位点的命运，这反映了细胞在进入前命运决定的可塑性。第一批通过原条进入的上胚层细胞是那些产生胚外中胚层的细胞。将形成卵黄囊和羊膜中胚层的细胞构成了原条中期胚胎中胚层层的主要部分。注定形成胚胎中胚层的细胞仍存在于上胚层中，但一些已被招募到中胚层的远端部分。到原条后期，中胚层层仅包含胚胎中胚层的前体。这表明中条中胚层逐渐向胚外位点移位，这让人想起在上覆内胚层组织中发生的情况。原条后期中胚层中细胞命运的区域化与其在上胚层中细胞进入前的祖先具有相同的空间关系。这意味着细胞在近端-远端轴上的位置及其与原条的接近程度是胚胎中胚层模式形成的主要决定因素。
