NEUROD2 AND NEUROD3 - DISTINCT EXPRESSION PATTERNS AND TRANSCRIPTIONAL ACTIVATION POTENTIALS WITHIN THE NEUROD GENE FAMILY

We have identified two new genes, neuroD2 and neuroD3, on the basis of their similarity to the neurogenic basic-helix-loop-helix (bHLH) gene neuroD. The predicted amino acid sequence of neuroD2 shows a high to neuroD and MATH-2/NEX-1 in the bHLH region, whereas neuroD3 is a more distantly related family member, neuroD3 is expressed transiently duri ng embryonic development, with the highest levels of expression betwee n days 10 and 12, neuroD2 is initially expressed at embryonic day II, with persistent expression in the adult nervous system, In situ and No rthern (RNA) analyses demonstrate that different regions of the adult nervous system have different relative amounts of neuroD and neuroD2 R NA. Similar to neuroD, expression of neuroD2 in developing Xenopus lae vis embryos results in ectopic neurogenesis, indicating that neuroD2 m ediates neuronal differentiation. Transfection of vectors expressing n euroD and neuroD2 into P19 cells shows that both can activate expressi on through simple E-box-driven reporter constructs and can activate a reporter driven by the neuroD2 promoter legion, but the GAP-43 promote r is preferentially activated by neuroD2, The noncongruet expression p attern and target gene specificity of these highly related neurogenic bHLH proteins make them candidates for conferring specific aspects of the neuronal phenotype.