More then 20 mammalian Antennapedia (1)-class (class 1) homeo box genes are expressed in the developing central nervous system (CNS). Their expression patterns are spatially restricted along both the antero-posterior and dorso-ventral axes. The spatial restrictions within the dorso-ventral axis of the CNS are limited and often extend over many cell layers. These genes generally have different anterior boundaries of expression that are never anterior to the hindbrain. Expression patterns of several divergent homeobox genes have fundamental differences from those of the class 1 genes. En-1 and Evx-1, the murine homologs of the Drosophila engrailed and even-skipped genes respectively, show a much greater localization of transcripts along the dorso-ventral axis. En-1, En-2, Dlx, Tes-1 and some members of the POU gene family are expressed more anteriorly than the hindbrain. Among these Dbx, Dlx, Tes-1, and the POU homeobox genes Brn-1, Brn-2, and Tst-1 are detected in the telencephalon. The telencepholon is an evolutionary unique structure in chordates and is of great interest neurologically. Little is known about the molecular mechanism underlying the regulation of telencephalon development.
See also: "Spatial expression patterns".