Lawson Aaron, Schoenwolf Gary C
Department of Neurobiology and Anatomy, and Children's Health Research Center, University of Utah School of Medicine, Salt Lake City, UT 84132-3401, USA.
Development. 2003 Aug;130(15):3491-501. doi: 10.1242/dev.00579.
Gastrulation is characterized by the extensive movements of cells. Fate mapping is used to follow such cell movements as they occur over time, and prospective fate maps have been constructed for several stages of the model organisms used in modern studies in developmental biology. In chick embryos, detailed fate maps have been constructed for both prospective mesodermal and ectodermal cells. However, the origin and displacement of the prospective endodermal cells during crucial periods in gastrulation remain unclear. This study had three aims. First, we determined the primitive-streak origin of the endoderm using supravital fluorescent markers, and followed the movement of the prospective endodermal cells as they dispersed to generate the definitive endodermal layer. We show that between stages 3a/b and 4, the intraembryonic definitive endoderm receives contributions mainly from the rostral half of the primitive streak, and that endodermal movements parallel those of ingressing adjacent mesodermal subdivisions. Second, the question of the epiblast origin of the endodermal layer was addressed by precisely labeling epiblast cells in a region known to give rise to prospective somitic cells, and following their movement as they underwent ingression through the primitive streak. We show that the epiblast clearly contributes prospective endodermal cells to the primitive streak, and subsequently to definitive endoderm of the area pellucida. Finally, the relationship between the hypoblast and the definitive endoderm was defined by following labeled rostral primitive-streak cells over a short period of time as they contributed to the definitive endoderm, and combining this with in situ hybridization with a riboprobe for Crescent, a marker of the hypoblast. We show that as the definitive endodermal layer is laid down, there is cell-cell intercalation at its interface with the displaced hypoblast cells. These data were used to construct detailed prospective fate maps of the endoderm in the chick embryo, delineating the origins and migrations of endodermal cells in various rostrocaudal levels of the primitive streak during key periods in early development.
原肠胚形成的特点是细胞的广泛运动。命运图谱用于追踪细胞随时间发生的此类运动，并且已经为发育生物学现代研究中使用的几种模式生物的多个阶段构建了预期命运图谱。在鸡胚中，已经为预期的中胚层和外胚层细胞构建了详细的命运图谱。然而，原肠胚形成关键时期预期内胚层细胞的起源和位移仍不清楚。本研究有三个目标。首先，我们使用活体荧光标记确定内胚层的原条起源，并追踪预期内胚层细胞分散以形成确定内胚层层时的运动。我们表明，在3a/b期和4期之间，胚胎内确定的内胚层主要来自原条的头侧一半，并且内胚层运动与相邻中胚层亚群的侵入运动平行。其次，通过精确标记已知产生预期体节细胞区域的上胚层细胞，并追踪它们通过原条侵入时的运动，解决了内胚层层上胚层起源的问题。我们表明，上胚层明显为原条贡献预期的内胚层细胞，随后为明区的确定内胚层贡献细胞。最后，通过在短时间内追踪标记的头侧原条细胞对确定内胚层的贡献，并将其与用新月体的核糖探针进行原位杂交相结合，确定了下胚层与确定内胚层之间的关系，新月体是下胚层的一个标记。我们表明，随着确定内胚层层的形成，在其与移位的下胚层细胞的界面处存在细胞间插入。这些数据用于构建鸡胚内胚层的详细预期命运图谱，描绘了早期发育关键时期原条不同头尾水平内胚层细胞的起源和迁移。
