Fig. 5.

Colocalization of neuronal bHLH differentiation factors by in situ hybridization (embryonic day 14). Immediately adjacent parasagittal sections of rat embryos were hybridized with riboprobes specific for NEX(A, E), neuroD(B, F), and NDRF(C, G). For better orientation, one adjacent section was stained with thionin (Thio;D, H).A–C, Overviews reveal highly overlapping expression patterns of NEX, neuroD, andNDRF in the cortical neuroepithelium of the telencephalon (arrow 1 in A). Lining the 4th ventricle (arrow 2), the spinal trigeminal nucleus and the principal sensory trigeminal nucleus are also stained with all three probes. Note the absence of expression of either bHLH gene outside the nervous system (the pancreatic expression ofneuroD/β2 is not visible in the plane of this section). Some regions are only expressing the neuroDgene, including the olfactory neuroepithelium (arrow 3in B) and the dorsal root ganglia (arrow 4). E–G, Higher magnification of the dorsal telencephalon reveals colocalization of all three transcripts in the cortical preplate (pp inE) and the absence of the transcripts from the ventricular zone (vz) lining the lateral ventricle (lv). Note the rostral and caudal expression boundaries and the absence of either transcript from the basal telencephalon (bt). At E14, a more prominent expression ofneuroD (compared with NEX andNDRF expression) is seen in the neuroepithelium of the hippocampus (arrow 5 in F) and amygdala (arrow 6). No hybridization signal was obtained with sense-orientated probes (data not shown).