The contribution made by a single somite to the vertebral column: experimental evidence in support of resegmentation using the chick-quail chimaera model.

The somitic involvement in the formation of the vertebral column was examined using the chick-quail chimaera model. Single cervical somites from quail donor embryos were transplanted into similarly staged chick host embryos. Following further incubation, serial sections of variously staged embryos were stained with the Feulgen reaction to distinguish the two cell populations. Quail cells were generally located within a delimited region in one half of each of the two adjacent vertebrae, as well as in the intervening disc. The horizontal plane of division through each vertebra passed approximately through the centre of the body and divided the neural arch into rostral and caudal halves through the rostral border of the caudal notch. These results give support to the controversial theory of resegmentation, in which it was suggested that there is an apparent realignment of segmentation between the somite stage and the subsequent vertebral stage of development.