Pax genes and sclerotome development

Differentiation of somites leads to the development of dermomyotome and sclerotome with the latter forming after an epithelial-mesenchymal transition of the ventral part of the somite. Inductive effects of the notochord are required for differentiation of the sclerotome and for proper formation of the axial skeleton, the inductive effect of the notochord being mediated by sonic hedgehog (SHH), the mammalian homologue of the Drosophila segment polarity gene hedgehog. Shh acts by antagonizing the activity of the cAMP dependent protein kinase A (Pka). Pax1 and Pax9 are paired box containing genes expressed in the developing sclerotome that may be involved in mediating the inductive effects of the notochord. Loss of Pax1 function in mice leads to severe abnormalities in sclerotome differentiation and vertebral column formation.