D'Amico L A, Cooper M S
Department of Zoology and Center for Developmental Biology, University of Washington, Seattle, Washington 98195-1800, USA.
Dev Dyn. 2001 Dec;222(4):611-24. doi: 10.1002/dvdy.1216.
The yolk syncytial layer (YSL) of the teleostean yolk cell is known to play important roles in the induction of cellular mesendoderm, as well as the patterning of dorsal tissues. To determine how this extraembryonic endodermal compartment is subdivided and morphologically transformed during early development, we have examined collective movements of vitally stained YSL nuclei in axiating zebrafish embryos by using four-dimensional confocal microscopy. During blastulation, gastrulation, and early segmentation, zebrafish YSL nuclei display several highly patterned movements, which are organized into spatially distinct morphogenetic domains along the anterior-posterior and dorsal-ventral axes. During the late blastula period, with the onset of epiboly, nuclei throughout the YSL initiate longitudinal movements that are directed along the animal-vegetal axis. As epiboly progresses, nuclei progressively recede from the advancing margin of the epibolic YSL. However, a small group of nuclei is retained at the YSL margin to form a constricting blastoporal ring. During mid-gastrulation, YSL nuclei undergo convergent-extension behavior toward the dorsal midline, with a subset of nuclei forming an axial domain that underlies the notochord. These highly patterned movements of YSL nuclei share remarkable similarities to the morphogenetic movements of deep cells in the overlying zebrafish blastoderm. The macroscopic shape changes of the zebrafish yolk cell, as well as the morphogenetic movements of its YSL nuclei, are homologous to several morphogenetic behaviors that are regionally expressed within the vegetal endodermal cell mass of gastrulating Xenopus embryos. In contrast to the cellular endoderm of Xenopus, the dynamics of zebrafish YSL show that a syncytial endodermal germ layer can express a temporal sequence of morphogenetic domains without undergoing progressive steps of cell fate restriction.
硬骨鱼类卵黄细胞的卵黄合胞体层（YSL）在诱导细胞中胚层以及背侧组织的模式形成中发挥着重要作用。为了确定这个胚外内胚层区域在早期发育过程中是如何细分和形态转变的，我们使用四维共聚焦显微镜检查了经活体染色的斑马鱼胚胎中YSL细胞核的集体运动。在囊胚形成、原肠胚形成和早期体节形成过程中，斑马鱼YSL细胞核表现出几种高度有序的运动，这些运动沿着前后轴和背腹轴组织成空间上不同的形态发生域。在囊胚后期，随着外包的开始，整个YSL中的细胞核开始沿动植物轴进行纵向运动。随着外包的进行，细胞核逐渐从外包YSL的推进边缘后退。然而，一小群细胞核保留在YSL边缘形成一个收缩的胚孔环。在原肠胚中期，YSL细胞核向背中线进行汇聚延伸行为，其中一部分细胞核形成位于脊索下方的轴向域。YSL细胞核的这些高度有序的运动与斑马鱼胚盘上层深层细胞的形态发生运动有显著相似之处。斑马鱼卵黄细胞的宏观形状变化及其YSL细胞核的形态发生运动与非洲爪蟾原肠胚植物内胚层细胞团中局部表达的几种形态发生行为同源。与非洲爪蟾的细胞内胚层不同，斑马鱼YSL的动态变化表明，合胞体的内胚层胚层可以表达形态发生域的时间序列，而无需经历细胞命运限制的渐进步骤。
