Dockter J L, Ordahl C P
Department of Anatomy and the Cardiovascular Research Institute, Box 0452, University of California San Francisco, San Francisco, CA 94143-0452, USA.
Development. 1998 Jun;125(11):2113-24. doi: 10.1242/dev.125.11.2113.
When the somite first forms the cells appear to be equivalent in potential. In order to understand the lineage diversification of the somite, the determination of sclerotome cells to the cartilage fate was tested using an in vivo challenge assay in which quail sclerotome fragments were grafted into a dorsal position in a chick host. Grafts containing undetermined cells were expected to differentiate into other tissues while grafts containing determined chondrocyte precursors were expected to consistently give rise to cartilage. We found that grafted sclerotome fragments from somite stages V-XX were capable of giving rise to integrated muscle and dermis and that it was not until fragments from stage XII somites were grafted that cartilage was consistently produced in the assay. Sclerotomal tissue from embryonic day 4-6 embryos remained as morphologically unintegrated mesenchyme when grafted into an embryonic day 2 host, but formed only cartilage when placed into an identically aged host. Vertebral body cartilage from embryonic day 7 and embryonic day 8 embryos formed exclusively ectopic cartilage in an embryonic day 2 host. We conclude that cells determined to the cartilage fate do not appear until somite stage XII, but that not all sclerotome cells are determined at this time. The effect of host age on the differentiation and morphogenetic behavior of sclerotome fragment grafts in this assay indicate the existence of developmental eras within the embryo.
当体节最初形成时，细胞在潜能上似乎是等同的。为了了解体节的谱系分化，利用体内挑战试验检测了硬骨节细胞向软骨命运的定向，该试验中，将鹌鹑硬骨节片段移植到鸡宿主的背部位置。含有未定向细胞的移植物预期会分化为其他组织，而含有定向软骨细胞前体的移植物预期会持续产生软骨。我们发现，来自体节V-XX期的移植硬骨节片段能够产生整合的肌肉和真皮，并且直到移植来自 XII 期体节的片段时，试验中才持续产生软骨。当将来自胚胎第4-6天胚胎的硬骨节组织移植到胚胎第2天的宿主中时，它保持为形态上未整合的间充质，但当置于相同年龄的宿主中时仅形成软骨。来自胚胎第7天和胚胎第8天胚胎的椎体软骨在胚胎第2天的宿主中仅形成异位软骨。我们得出结论，直到体节 XII 期才出现定向为软骨命运的细胞，但此时并非所有硬骨节细胞都已定向。在该试验中宿主年龄对硬骨节片段移植物的分化和形态发生行为的影响表明胚胎内存在发育阶段。
