Department of Cell Recognition, Tokyo Metropolitan Institute of Gerontology, Sakaecho, Itabashi-ku, Tokyo, Japan.
NB-3 is a neural recognition molecule which is a member of contactin/F3 subgroup in the immunoglobulin superfamily. We report here the developmental expression pattern and localization of NB-3 mRNA in mouse brain, determination of the NB-3 gene organization and identification of the promoter region. We also describe a splicing isoform of mouse NB-3. Mouse NB-3 exhibited 96% identity with rat NB-3 at the amino acid sequence level. The splicing isoform lacked the amino acid residues between 62 and 78 of the original NB-3, which constituted a part of the first immunoglobulin-like domain. The expression of NB-3 mRNA was evident after birth, reaching a maximum at the postnatal seventh day, and declined thereafter in the cerebrum, whereas the mRNA increased in the cerebellum to adulthood. In situ hybridization demonstrated that NB-3 mRNA was preferentially expressed in the accessory olfactory bulb, layers II/III and V of the cerebral cortex, piriform cortex, anterior thalamic nuclei, locus coeruleus of the pons and mesencephalic trigeminal nucleus, and in Purkinje cells of the cerebellum. The mouse NB-3 gene consisted of 23 exons spanning more than 130kb. The overall organization of the gene was similar to those of the F11, axonin-1 and TAX-1 genes of the subgroup. By reporter gene analysis with the 5'-flanking region of the gene, we found a basal promoter activity in the 1.2kb fragment upstream of the putative transcription initiation site. This study provides a basis for elucidating the biological significance of the contactin/F3 subgroup molecules.