The role of Xmsx-2 in the anterior-posterior patterning of the mesoderm in Xenopus laevis

Many molecules are involved in defining mesodermal patterning of the Xenopus embryo. In this paper, evidence is provided that a member of the msx family of genes, the Xmsx-2 gene, is involved in anterior-posterior patterning of the mesoderm. A comparison of its sequence to another previously cloned msx-2 Xenopus homolog, Xhox-7.1' 45] showed that they are closely related. The Xmsx-2 gene is first expressed at midgastrulation predominantly in the dorsal part of the embryo. It showed a complex pattern of spatial expression, consistent with a role in patterning of the anterior-posterior axis. This inference is confirmed by gain-of-function experiments in which overexpressed msx-2 mRNA in developing Xenopus embryos resulted in embryos lacking anterior structures. Analysis of markers in mutant embryos showed that genes involved in ventral-posterior patterning such as Xhox-3, Xwnt-8, and Xvent-1 were upregulated, confirming the posteriorized nature of the embryos. We believe that the Xmsx-2 gene is involved in refining the patterning of the anterior-posterior part of the dorsal mesoderm after the initial signals determining the dorsal or ventral nature of the mesoderm have been specified.