Huang R, Zhi Q, Patel K, Wilting J, Christ B
Anatomisches Institut der Universität Freiburg, Germany.
Anat Embryol (Berl). 2000 Nov;202(5):375-83. doi: 10.1007/s004290000131.
Controversy has surrounded the process of resegmentation of cervico-occipital somites. We have reinvestigated this topic by grafting single somites of quail embryos homotopically into chick embryos. Somites one to five contribute to the skull. Somites one and two contribute to the parasphenoid, which develops by direct ossification in a non-segmental fashion. All cartilaginous derivatives of the somites are segmental. Somite two forms a stripe of cells in the basioccipital, exoccipital and supraoccipital. Somites three to five give rise to the subsequent caudal parts of the basioccipital and exoccipital. Somite five forms the first motion segment including the occipital condyle, the cranial part of the atlas and the tip of the dens axis. Therefore, the border between head and neck is in the centre of somite five, and corresponds to the expression boundary of Choxb-3. Somite six forms the caudal part of the atlas and the cranial part of the axis. Somites two to eight all contribute to the cranio-cervical muscles with the exception of the Mm. rectus capitis dorsalis and ventralis and the M. biventer cervicis, which do not receive contributions from somite two. In contrast, the M. cucullaris capitis is exclusively formed by myogenic cells from somite two, which parallels its exclusive innervation by the accessory nerve. Our data confirm the segmental nature of the occiput, and show that resegmentation is a very regular process involving all except the four cranialmost somites. Except for somites one and two, all of the somites contribute to the muscles located at the appropriate levels.
枕颈部体节重新分割的过程一直存在争议。我们通过将鹌鹑胚胎的单个体节原位移植到鸡胚胎中，对这一主题进行了重新研究。第一至五体节参与颅骨的形成。第一和二体节参与蝶骨体的形成，蝶骨体通过非节段性的直接骨化发育而成。体节的所有软骨衍生物都是节段性的。第二体节在枕骨基部、枕骨外侧部和枕骨上部形成一条细胞带。第三至五体节形成枕骨基部和枕骨外侧部随后的尾部部分。第五体节形成包括枕髁、第一颈椎的颅骨部分和枢椎齿突尖端的第一个运动节段。因此，头与颈的边界在第五体节的中部，与Choxb - 3的表达边界相对应。第六体节形成第一颈椎的尾部部分和枢椎的颅骨部分。第二至八体节都参与颅颈肌的形成，但头背直肌、头腹直肌和颈二腹肌除外，它们不接受第二体节的贡献。相反，头肌环肌完全由来自第二体节的肌原性细胞形成，这与其由副神经的独特支配相对应。我们的数据证实了枕部的节段性本质，并表明重新分割是一个非常规律的过程，除了最前面的四个体节外，所有体节都参与其中。除了第一和二体节外，所有体节都对位于相应水平的肌肉有贡献。
