Lawson K A, Meneses J J, Pedersen R A
Hubrecht Laboratory, Netherlands Institute for Developmental Biology, Utrecht.
Development. 1991 Nov;113(3):891-911. doi: 10.1242/dev.113.3.891.
The fate of cells in the epiblast at prestreak and early primitive streak stages has been studied by injecting horseradish peroxidase (HRP) into single cells in situ of 6.7-day mouse embryos and identifying the labelled descendants at midstreak to neural plate stages after one day of culture. Ectoderm was composed of descendants of epiblast progenitors that had been located in the embryonic axis anterior to the primitive streak. Embryonic mesoderm was derived from all areas of the epiblast except the distal tip and the adjacent region anterior to it: the most anterior mesoderm cells originated posteriorly, traversing the primitive streak early; labelled cells in the posterior part of the streak at the neural plate stage were derived from extreme anterior axial and paraxial epiblast progenitors; head process cells were derived from epiblast at or near the anterior end of the primitive streak. Endoderm descendants were most frequently derived from a region that included, but extended beyond, the region producing the head process: descendants of epiblast were present in endoderm by the midstreak stage, as well as at later stages. Yolk sac and amnion mesoderm developed from posterolateral and posterior epiblast. The resulting fate map is essentially the same as those of the chick and urodele and indicates that, despite geometrical differences, topological fate relationships are conserved among these vertebrates. Clonal descendants were not necessarily confined to a single germ layer or to extraembryonic mesoderm, indicating that these lineages are not separated at the beginning of gastrulation. The embryonic axis lengthened up to the neural plate stage by (1) elongation of the primitive streak through progressive incorporation of the expanding lateral and initially more anterior regions of epiblast and, (2) expansion of the region of epiblast immediately cranial to the anterior end of the primitive streak. The population doubling time of labelled cells was 7.5 h; a calculated 43% were in, or had completed, a 4th cell cycle, and no statistically significant regional differences in the number of descendants were found. This clonal analysis also showed that (1) growth in the epiblast was noncoherent and in most regions anisotropic and directed towards the primitive streak and (2) the midline did not act as a barrier to clonal spread, either in the epiblast in the anterior half of the axis or in the primitive streak. These results taken together with the fate map indicate that, while individual cells in the epiblast sheet behave independently with respect to their neighbours, morphogenetic movement during germ layer formation is coordinated in the population as a whole.
通过将辣根过氧化物酶（HRP）注射到6.7天龄小鼠胚胎的单个原位细胞中，并在培养一天后，在原条中期至神经板阶段鉴定标记的后代，研究了原条期和早期原条期上胚层细胞的命运。外胚层由位于原条前方胚胎轴中的上胚层祖细胞的后代组成。胚胎中胚层来源于上胚层的所有区域，除了远端尖端及其前方的相邻区域：最前端的中胚层细胞起源于后方，早期穿过原条；神经板阶段原条后部的标记细胞来源于极前端的轴旁和轴上胚层祖细胞；头部突起细胞来源于原条前端或其附近的上胚层。内胚层后代最常来源于一个包括但不限于产生头部突起的区域：上胚层的后代在原条中期以及后期阶段出现在内胚层中。卵黄囊和羊膜中胚层由后外侧和后部上胚层发育而来。由此产生的命运图谱与鸡和有尾两栖类的基本相同，表明尽管存在几何差异，但这些脊椎动物之间的拓扑命运关系是保守的。克隆后代不一定局限于单个胚层或胚外中胚层，这表明这些谱系在原肠胚形成开始时并未分离。胚胎轴在神经板阶段之前通过以下方式延长：（1）通过逐渐纳入不断扩大的上胚层外侧和最初更靠前的区域，使原条伸长；（2）使紧邻原条前端头部的上胚层区域扩大。标记细胞的群体倍增时间为7.5小时；计算得出43%的细胞处于或已完成第4个细胞周期，并且在后代数量上未发现统计学上显著的区域差异。这种克隆分析还表明：（1）上胚层的生长是不连贯的，并且在大多数区域是各向异性的，朝着原条方向；（2）中线在轴前半部分的上胚层或原条中都不构成克隆扩散的障碍。这些结果与命运图谱一起表明，虽然上胚层片中的单个细胞相对于其邻居独立行为，但胚层形成过程中的形态发生运动在整个群体中是协调的。
