DLX-P, MASH-1, AND MAP-5 EXPRESSION AND BROMODEOXYURIDINE INCORPORATION DEFINE MOLECULARLY DISTINCT CELL-POPULATIONS IN THE EMBRYONIC MOUSEFOREBRAIN

Recently, the Dlx family of homeobox genes have been identified as can didates for regulating patterning and differentiation of the forebrain . We have made a polyclonal antiserum to the protein product of the Dl x-2 gene. Using this antiserum, we have characterized the spatial and temporal pattern of DLX-2 protein expression during murine development and in the adult mouse brain. These studies demonstrate that, like th e mRNA from the Dlx-2 gene, DLX-2 protein is expressed in mouse embryo nic forebrain, limbs, tail, genital tubercle, and branchial arches. Wi thin the embryonic forebrain, DLX-2 protein is expressed within specif ic transverse and longitudinal domains. Analysis of expression within the wall of the forebrain shows that DLX-2 is expressed in proliferati ve regions including the ventricular and subventricular zones. DLX-2 i s expressed in the same cells as MASH-1, a marker of relatively undiff erentiated cells, but in a reciprocal fashion to MAP-2, a marker of te rminal neuronal differentiation. A number of DLX-2-expressing cells, b ut not all, can be labeled with bromodeoxyuridine (BrdU). Using the pa tterns of DLX-2, MASH-1, MAP-2 expression, and bromodeoxyuridine incor poration, we identify four molecularly distinct populations of cells t hat may correspond to different stages of neuronal differentiation in the mouse basal forebrain, in which DLX-2 is expressed at the transiti on from proliferation to terminal differentiation.