Structure and expression of the mouse necdin gene. Identification of a postmitotic neuron-restrictive core promoter.

Necdin is a 325 amino acid residue protein encoded by a cDNA clone isolated from neurally differentiated embryonal carcinoma cells. In situ hybridization histochemistry revealed that necdin mRNA-containing cells in vivo coincided with postmitotic neurons in the mouse brain from early periods of neurogenesis until adulthood. To study the regulation of necdin gene expression, we have isolated and characterized the necdin gene from a mouse genomic DNA library. The necdin gene contains no intron, and its upstream region lacks canonical TATA and CAAT boxes. To assess promoter activity, the 5'-flanking sequence (844 base pairs) of the necdin gene was fused to the LacZ reporter gene and transiently transfected into retinoic acid-treated P19 embryonal carcinoma cells. Most of the transfectants expressing high levels of LacZ immunoreactivity were postmitotic neurons differentiated from P19 cells. Deletion analysis using luciferase reporter genes demonstrated that a neuron-restrictive core promoter is localized to positions -80 to -35, in which a G+C-rich domain and a putative binding site for transcription factors with PAS (per, arnt, and single-minded) dimerization domain are comprised. These results suggest that postmitotic neuron-restrictive expression of the necdin gene is mediated by the specific cis-acting elements and that this promoter is applicable to postmitotic neuron-targeted expression of various transgenic systems.