Expression of the genes GAD67 and Distal-less-4 in the forebrain of Xenopus laevis confirms a common pattern in tetrapods.
We investigated whether gamma-amino butyric acidergic (GABAergic) cell populations correlate positionally with specific Dlx-expressing histogenetic territories in an anamniote tetrapod, the frog Xenopus laevis. To that end, we cloned a fragment of Xenopus GAD67 gene (xGAD67, expressed in GABAergic neurons) and compared its expression with that of Distal-less-4 gene (xDll-4, ortholog of mouse Dlx2) in the forebrain at late larval and adult stages. In Xenopus, GABAergic neurons were densely concentrated in xDll-4-positive territories, such as the telencephalic subpallium, part of the hypothalamus, and ventral thalamus, where nearly all neurons expressed both genes. In contrast, the pallium of Xenopus generally contained dispersed neurons expressing xGAD67 or xDll-4, which may represent local circuit neurons. As in amniotes, these pallial interneurons may have been produced in the subpallium and migrated tangentially into the pallium during development. In Xenopus, the ventral division of the classic lateral pallium contained extremely few GABAergic cells and showed only low signal of the pallial gene Emx1, suggesting that it may represent the amphibian ventral pallium, homologous to that of amniotes. At caudal forebrain levels, a number of GABAergic neurons was observed in several areas (dorsal thalamus, pretectum), but no correlation to xDll-4 was observed there. The location of GABAergic neurons in the forebrain and their relation to the developmental regulatory genes Dll and Dlx were very similar in Xenopus and in amniotes. The close correlation in the expression of both genes in rostral forebrain regions supported the notion that Dll/Dlx are among the genes involved in the acquisition of the GABAergic phenotype.
Department of Human Anatomy, Faculty of Medicine, University of Murcia, 30100 Murcia, Spain.
Aurora
A
Brox
Luis
L
Puelles
Beatriz
B
Ferreiro
Loreta
L
Medina
D000818:Animals; D015870:Gene Expression; D005968:Glutamate Decarboxylase / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D016548:Prosencephalon / Q000201:enzymology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014018:Tissue Distribution; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000235:genetics / Q000378:metabolism*
D018398:Homeodomain Proteins; D007527:Isoenzymes; D029867:Xenopus Proteins; C470088:dll4 protein, Xenopus; D005968:Glutamate Decarboxylase; C402565:glutamate decarboxylase 1