REGIONALIZED EXPRESSION OF THE DBX FAMILY HOMEOBOX GENES IN THE EMBRYONIC CNS OF THE MOUSE

Here we report the identification of a novel homeobox gene family Dbx in mouse, which consists of Dbx and Dbx2. The two genes share similar structural organization and are encoded by different chromosomes. The predicted Dbx and Dbx2 proteins share 85% identity in their homeodomai n amino acid sequences, but otherwise showed no significant similarity . Characterization of the expression of these two genes in the embryos suggested their role in the development of the CNS. In the forebrain, Dbx is expressed in various regions, while Dbx2 showed a more restric ted pattern of expression. In the midbrain, the expression domains of Dbx and Dbx2 overlap along the dorso-lateral wall of the ventricle. In the hindbrain and spinal cord, both genes are expressed in the bounda ry separating the basal and alar plates, which seems to correspond to the sulcus limitans. Expression of the Dbx/Dbx2 genes is restricted to the ventricular region of the embryonic CNS except for that of Dbx in the septum of the telencephalon. Together these observations indicate possible participation of the members of the Dbx family in regionaliz ation of the CNS. While the expression of Dbx was restricted to the CN S, Dbx2 was also expressed in some of the mesenchymal cells, such as l imb buds and tooth germs.