IDENTIFICATION OF A NOVEL NEURAL CELL-ADHESION MOLECULE-RELATED GENE WITH A POTENTIAL ROLE IN SELECTIVE AXONAL PROJECTION

We describe here the cloning of mouse complementary DNAs encoding a no vel protein, Rb-8 neural cell adhesion molecule (RNCAM), with a predic ted extracellular region of five immunoglobulin Ca-type domains follow ed by two fibronectin type III domains, Alternative splicing is likely to generate two RNCAM isoforms, which are differently attached to the cell membrane, These structural features and overall sequence identit y identify this protein as a novel member of a cell adhesion molecule subgroup together with vertebrate neural cell adhesion molecule, Aplys ia cell adhesion molecule, and Drosophila fasciclin II, In insects, fa sciclin II is present on a restricted subset of embryonic central nerv ous system axons where it controls selective axon fasciculation. Intri guingly, RNCAM likewise is expressed in subsets of olfactory and vomer onasal neurons with topographically defined axonal projections, The sp atial expression RNCAM corresponds precisely to that of certain odoran t receptor expression zones of the olfactory epithelium. These express ion patterns thus render RNCAM the first described cell adhesion molec ule with a potential regulatory role in formation of selective axonal projections important for olfactory sensory information coding.