Regionalization of the axial skeleton derived from the somites: its ontogenesis and phylogenesis

在哺乳动物和鸟类的中轴骨骼中，肋骨只在胸部区域。 肋的大部分由远侧肋组成，远侧肋依赖于表面外胚层发育。 因此，中轴骨的区域化被认为是远端肋骨根据其位置的差异性发育。 将2天鸡胚胸体节异位移植到腰骶部，形成了比正常肋骨短的异位肋骨。 在该嵌合体的发育过程中，我们发现胸体节细胞在遇到腰骶侧板中胚层时停止了迁移，另一方面，我们比较了鸡胚和小鼠胚胎的中轴骨骼发育，发现骨化顺序不同，这与哺乳动物和鸟类的生殖过程中中轴骨骼的区域化独立发生的观点一致。

In the axial skeleton of mammals and birds, the ribs are exclusively in the thoracic region. The most part of the rib is consisuted of the distal rib, which develops depending on the surface ectoderm. Regionalization of the axial skeleton is, thus, considered to be differential development of the distal rib according to its location. An ectopic transplantation of the thoracic somite into the lumbosacral region in a 2-day chick embryo caused ectopic rib, which was shorter than the normal rib. In the course of development of this chimera, we found that the thoracic somite cells stopped their migration when they met the lumbosacral lateral plate mesoderm.On the other hand, we compared the axial skeleton development between chick embryos and mouse embryos and found that order of the ossification was different, which coincide with an idea that the regionalization of the axial skeleton independently occurs in the course of phylogenesis of mammals and birds.