CLONING OF HUMAN NEURONATIN GENE AND ITS LOCALIZATION TO CHROMOSOME-20Q11.2-12 - THE DEDUCED PROTEIN IS A NOVEL PROTEOLIPID

Human brain development is a continuum governed by differential gene; expression. Therefore, wt proceeded to identify genes selectively expr essed in the developing brain. Using differential display and library screening, a novel rat cDNA, neuronatin, was identified and used to sc reen a human fetal brain cDNA library. Human neuronatin cDNA was isola ted and sequenced. The cDNA was 1159 bp long and corresponded in size to the 1.25 kb message detected on Northern analysis. Neuronatin mRNA was selectively expressed in human brain during fetal development, but became repressed in adulthood. When studied in the rat, neuronatin mR NA first appeared at mid-gestation in association with the onset of ne urogenesis, becoming most pronounced later in development when neuroep ithelial proliferation and neuroblast commitment are manifest, and dec lined postnatally coinciding with the completion of neurogenesis. The deduced protein has two distinct domains, a hydrophobic N-terminal and basic C-terminal rich in arginine residues. Both the amino acid seque nce and secondary structure of this amphipathic polypeptide exhibited homology to PMP1 and phospholamban members of the 'proteolipid' class of proteins which function as regulatory subunits of membrane channels . The neuronatin gene, 3973 bases long, contains in its 5'-flanking re gion a neural restrictive silencer element which may govern neuron-spe cific expression. Based on screening a somatic cell hybrid panel, neur onatin gene was assigned to chromosome-20. And, using deletion constru cts of chromosome-20 and fluorescence in situ hybridization, neuronati n was localized to chromosome-20q11.2-12. In conclusion, neuronatin is a novel human gene that is developmentatally regulated and expressed in the brain. The deduced protein is a proteolipid that may function a s a unique regulator of ion channels during brain development. The def initive localization of neuronatin to human chromosome 20q11.2-12 prov ides the basis to investigate this gene as a candidate in neuro-develo pmental diseases that may also map to this region.