Gbx2 expression in the late embryonic chick dorsal thalamus.

The expression pattern of the transcription factor gene Gbx2 in the forebrain of chicken embryos (embryonic day 14) was mapped using digoxigenin-labeled riboprobes and compared with the expression of the transcription factors Pax6 and Nkx2.2. The topographic analysis of Gbx2 expression on coronal and sagittal sections discriminated the positions and boundaries of diverse neuronal nuclei belonging to the dorsal thalamus from neighboring territories (the epithalamus, ventral thalamus, pretectum, and the underlying basal plate). The differential expression of Gbx2 within the dorsal thalamus clearly corresponds with the existence of four primary subdivisions identified in a previous study from this laboratory [13]: the anteroventral region and dorsal, intermediate, and ventral tiers. The subhabenular region turned out not to express Gbx2; this possibly implies it needs to be distinguished as a fifth separate dorsal thalamus subdivision.