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Mech Dev April 1, 2006; 123 (4): 321-33.

Interaction between X-Delta-2 and Hox genes regulates segmentation and patterning of the anteroposterior axis.

In vertebrates, the paraxial mesoderm already exhibits a complex Hox gene pattern by the time that segmentation occurs and somites are formed. The anterior boundaries of the Hox genes are always maintained at the same somite number, suggesting coordination between somite formation and Hox expression. To study this interaction, we used morpholinos to knockdown either the somitogenesis gene X-Delta-2 or the complete Hox paralogous group 1 (PG1) in Xenopus laevis. When X-Delta-2 is knocked down, Hox genes from different paralogous groups are downregulated from the beginning of their expression at gastrula stages. This effect is not via the canonical Notch pathway, as it is independent of the Notch effector Su(H). We also reveal for the first time a clear role for Hox genes in somitogenesis, as loss of PG1 gene function results in the perturbation of somite formation and downregulation of the X-Delta-2 expression in the PSM. This effect on X-Delta-2 expression is also observed during neurula stages, before the somites are formed. These results show that somitogenesis and patterning of the anteroposterior axis are closely linked via a feedback loop involving Hox genes and X-Delta-2, suggesting the existence of a coordination mechanism between somite formation and anteroposterior patterning. Such a mechanism is likely to be functional during gastrulation, before the formation of the first pair of somites, as suggested by the early X-Delta-2 regulation of the Hox genes.

PubMed ID: 16644189
Article link: Mech Dev

Genes referenced: bmp4 cad cdx4 dlc dll1 egr2 en2 fgf4 hes4 hes7.1 hes7.2 hoxa1 hoxb4 hoxb9 hoxc6 hoxc9-like hoxd1 myod1 notch1 tbxt
Morpholinos: dlc MO1 dlc MO2 hoxa1 MO1 hoxa1 MO2 hoxb1 MO1 hoxb1 MO2 hoxd1 MO1 hoxd1 MO2

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