The telencephalon of the frog Xenopus based on calretinin immunostaining and gene expression patterns.

To further understand the organization and evolution of the telencephalon, we analyzed in the frog Xenopus laevis the expression of the genes Distal-less-4 (Xdll-4, comparable to the mouse gene Dlx2) and GAD-67 (XGAD-67, expressed in GABAergic cells), and compared this with calretinin immunostaining and the cytoarchitecture of the telencephalon. Our results show that like in other vertebrates, the telencephalon of the frog Xenopus is divided into two major territories: a basal, subpallial region showing a high density of cells expressing Xdll-4 and XGAD-67, and a dorsal, pallial region showing only few, dispersed cells expressing these genes. The subpallial territory of the frog Xenopus includes the septum, the amphibian basal ganglia, some basal forebrain cholinergic cell groups and some amygdala nuclei. In the pallium of the frog Xenopus, medial, dorsal, lateral, and ventral parts could be distinguished, similar to those described in amniotes. In summary, the amphibian telencephalon shows a basic morphogenetic organization similar to that of amniotes, which suggests that this organization is common to the telencephalon of all tetrapods.