SPATIALLY RESTRICTED EXPRESSION OF DLX-1, DLX-2(TES-1), GBX-2, AND WNT-3 IN THE EMBRYONIC DAY 12.5 MOUSE FOREBRAIN DEFINES POTENTIAL TRANSVERSE AND LONGITUDINAL SEGMENTAL BOUNDARIES

The expression patterns of four genes that are potential regulators of development were examined in the CNS of the embryonic day 12.5 mouse embryo. Three of the genes, Dlx-1, Dlx-2 (Tes-1), and Gbx-2, encode ho meodomain-containing proteins, and one gene, Wnt-3, encodes a putative secreted differentiation factor. These genes are expressed in spatial ly restricted transverse and longitudinal domains in the embryonic neu ral tube, and are also differentially expressed within the wall of the neural tube. Dlx-1 and Dlx-2 are expressed in two separate regions of the forebrain in an identical pattern. The Gbx-2 gene is expressed in four domains, two of which share sharp boundaries with the domains of the Dlx genes. One boundary is in the basal telencephalon between dee p and superficial strata of the medial ganglionic eminence; the other boundary is in the diencephalon at the zona limitans intrathalamica. T he Wnt-3 gene is expressed in a dorsal longitudinal zone extending fro m the hindbrain into the diencephalon, where its expression terminates at the zona limitans intrathalamica. Reciprocal patterns of expressio n are found within the dorsal thalamus for the Gbx-2 and Wnt-3 genes. These findings are consistent with neuromeric theories of forebrain de velopment, and based upon them we suggest a model for forebrain segmen tation.