Determination of somite cells: independence of cell differentiation and morphogenesis.
Determination of somite cells: independence of cell differentiation and morphogenesis.
复制标题
体细胞的测定：细胞分化和形态发生的独立性。
作者：
H. Aoyama;Ken Asamoto
体节是脊椎动物在发育过程中短暂出现的中胚层结构。位于体节腹内侧的细胞分化成产生软骨的硬节，而体节的其他部分分化成产生肌肉和真皮的真皮肌节。硬结进一步分为吻侧的一半，其中神经嵴细胞定居和运动神经生长，和尾侧的一半。为了了解这些轴是何时确定的，以及它们如何支配以后的发育，特别是来自体节的软骨的形态发生，我们将2.5日龄鹌鹑胚胎新形成的3个尾部体节移植到大约相同年龄的鸡胚中，其中一些轴发生逆转。结果总结如下。(1)当移植逆转只有背腹轴，一天后，两个尾部体节引起了正常dermomyotomes和sclerotomes，而最喙体节引起了一个sclerotome异常位于外胚层下方。这些结果表明，背腹轴不是在体节形成时确定的，而是在体节形成后约3小时开始确定的。(2)当移植逆转只有rostrocaudal轴，两天后，背根神经节的雏形形成在尾侧（原来的喙）移植的巩膜。体节的喙尾轴在体节形成时就已确定。(3)当移植逆转的背腹和rostrocaudal轴，两天后的操作，sclerotomes来自未来dermomyotomal区域的体节显示，保持其原来的rostrocaudal轴，从神经节的雏形的位置判断。结合结果1和2，这表明，沿吻尾轴的巩膜细胞沿着的命运是事先确定的，并独立于体节细胞分化为皮肌节和巩膜节的决定。(4)在9.5日龄的嵌合体胚胎中，由吻尾反转体节衍生的椎骨和肋骨的形态沿吻尾轴沿着反转。研究表明，当体节从节段板形成时，源自体节的软骨形态本质上是由体节决定的。因此，脊柱的rostrocaudal模式由体节中胚层固有的因素控制，而不是由该中胚层和脊索和/或神经管之间的相互作用，分割后产生的。
Somites are mesodermal structures which appear transiently in vertebrates in the course of their development. Cells situated ventromedially in a somite differentiate into the sclerotome, which gives rise to cartilage, while the other part of the somite differentiates into dermomyotome which gives rise to muscle and dermis. The sclerotome is further divided into a rostral half, where neural crest cells settle and motor nerves grow, and a caudal half. To find out when these axes are determined and how they rule later development, especially the morphogenesis of cartilage derived from the somites, we transplanted the newly formed three caudal somites of 2.5-day-old quail embryos into chick embryos of about the same age, with reversal of some axes. The results were summarized as follows. (1) When transplantation reversed only the dorsoventral axis, one day after the operation the two caudal somites gave rise to normal dermomyotomes and sclerotomes, while the most rostral somite gave rise to a sclerotome abnormally situated just beneath ectoderm. These results suggest that the dorsoventral axis was not determined when the somites were formed, but began to be determined about three hours after their formation. (2) When the transplantation reversed only the rostrocaudal axis, two days after the operation the rudiments of dorsal root ganglia were formed at the caudal (originally rostral) halves of the transplanted sclerotomes. The rostrocaudal axis of the somites had therefore been determined when the somites were formed. (3) When the transplantation reversed both the dorsoventral and the rostrocaudal axes, two days after the operation, sclerotomes derived from the prospective dermomyotomal region of the somites were shown to keep their original rostrocaudal axis, judging from the position of the rudiments of ganglia. Combined with results 1 and 2, this suggested that the fate of the sclerotomal cells along the rostrocaudal axis was determined previously and independently of the determination of somite cell differentiation into dermomyotome and sclerotome. (4) In the 9.5-day-old chimeric embryos with rostrocaudally reversed somites, the morphology of vertebrae and ribs derived from the explanted somites were reversed along the rostrocaudal axis. The morphology of cartilage derived from the somites was shown to be determined intrinsically in the somites by the time these were formed from the segmental plate. The rostrocaudal pattern of the vertebral column is therefore controlled by factors intrinsic to the somitic mesoderm, and not by interactions between this mesoderm and the notochord and/or neural tube, arising after segmentation.