Analysis of relationship between somite segmentation and vertebra segmentation

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Formation of the vertebral body from somites involves a process called resegmentation, by which the caudal half of a sclerotome is combined with the rostral half of the next sclerotome. We examined the relationship between resegmentation and rostro-caudal patterning of somite by using the Uncx4.1-LacZ transgene. Our results suggested that in the thoracic and lumbar vertebrae, the Uncx4.1-expressing caudal sclerotome gave rise to the intervertebral disc (IVD) and rostral portion of the vertebral body (VB). In the cervical vertebrae, the caudal sclerotome contributed to the IVD and both ends of the VB. This finding suggests that the rostro-caudal gene expression boundary does not necessarily coincide with the resegmentation boundary. Expression analysis of IVD marker genes including Pax1 in the wild-type, Mesp2 KO, and Ripply1/2 DKO embryos also supported the idea that a metameric pattern of IVD/VB is generated independently of Mesp2/Ripply-mediated rostro-caudal patterning of somite.