XB-ART-14752Development June 1, 1998; 125 (11): 2099-111.
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Expression of the Emx-1 and Dlx-1 homeobox genes define three molecularly distinct domains in the telencephalon of mouse, chick, turtle and frog embryos: implications for the evolution of telencephalic subdivisions in amniotes.
Homologies between vertebrate forebrain subdivisions are still uncertain. In particular the identification of homologs of the mammalian neocortex or the dorsal ventricular ridge (DVR) of birds and reptiles is still a matter of dispute. To get insight about the organization of the primordia of the main telencephalic subdivisions along the anteroposterior axis of the neural tube, a fate map of the dorsal prosencephalon was obtained in avian chimeras at the 8- to 9-somite stage. At this stage, the primordia of the pallium, DVR and striatum were located on the dorsal aspect of the prosencephalon and ordered caudorostrally along the longitudinal axis of the brain. Expression of homeobox-containing genes of the Emx, Dlx and Pax families were used as markers of anteroposterior developmental subdivisions of the forebrain in mouse, chick, turtle and frog. Their expression domains delineated three main telencephalic subdivisions in all species at the onset of neurogenesis: the pallial, intermediate and striatal neuroepithelial domains. The fate of the intermediate subdivisions diverged, however, between species at later stages of development. Homologies between forebrain subdivisions are proposed based on the conservation and divergence of these gene expression patterns.
PubMed ID: 9570774
Article link: Development
Species referenced: Xenopus laevis
Genes referenced: dlx1 emx1l emx2 sult1a1
Article Images: [+] show captions
|Fig. 1. Telencephalic subdivisions in representative species of mammals (mouse), birds (chick), reptiles (turtle) and amphibians (frog). Schematic representation of transverse sections at comparable anteroposterior levels of the rostral telencephalon in adult mouse, chick, turtle and frog brains. The mouse telencephalon contains two main subdivisions the cortex (cx) and striatopallidum (st); the septum (s) and amygdalar (s) regions are also indicated. The putative homologs of the mouse striatopallidum (st) in the other species are depicted in green. This region is known as paleostriatum (pst) in the chick. The DVR of reptiles is a large structure of the lateral telencephalic wall which bulges into the ventricle. It separates the dorsal cortex (dc) from the striatum (st). The complex formed by the neostriatum (n) and the hyperstriatum ventrale (hv) in birds is considered to be the homolog of the reptilian DVR. a, amygdala; cx, cerebral cortex; dc, dorsal cortex; dp, dorsal pallium; DVR, anterior dorsal ventricular ridge; hv, hyperstriatum; lp, lateral pallium; mp, medial pallium; n, neostriatum; pst, paleostriatum; s, septum; st, striatum.|
|Fig. 8. Interpretative scheme of the evolution of telencephalic regionalization. The adult structures produced by the three main subdivisions of the telencephalic vesicle neuroepithelium are depicted in different species based on the results of the present study (see text for details). The ‘pallial’ territory is shown in red, the ‘intermediate’ territory in blue and the ‘basal’ territory in green. Same abbreviations as in Fig. 1.|