Inherited variations in catecholamine metabolism are thought to underlie individual differences in neurophysiology and susceptibility to disease. These studies are aimed at understanding the genetic basis of variations in the structure and regulation of monoamine oxidases (MAO, E.C.1.4.3.4.), the enzymes primarily responsible for the degradation of amine neurotransmitters. Efforts will be directed first to cloning cDNAs for MAO using mRNA from several species - bovine, rodent and human, and several molecular biologic strategies including expression vector libraries, immunoaffinity purification of mRNA and synthetic oligonucleotides. Molecular genetic and biochemical methods will then be used to determine whether the A and B forms of MAO, which appear to have different structures and discrete functions in the nervous system, are encoded in separate genes and subject to distinct regulatory controls. Genes will be isolated from human genomic libraries and characterized with respect to sequence and intron/exon positions. Their chromosomal location will be determined using somatic cell hybrids and/or in situ hybridization to metaphase chromosomes. Linkage analyses will be carried out in human pedigrees to establish whether inherited variations in platelet MAO-B activity are determined by the structural gene for MAO-B using DNA polymorphisms and genomic blotting. Regulation of gene expression will be monitored by the sizes and amount of mRNA present under culture conditions where levels of MAO-A or MAO-B are changing. These include increased MAO-A activity in rat sympathetic neurons manifesting adrenergic versus cholinergic phenotype and in human skin fibroblasts exposed to glucocorticoids, as well as elevation of MAO-B activity in newborn mouse astrocytes as they proceed through their normal developmental sequence. Monoamine oxidase offers several intriguing phenomena for understanding neural functions - how multiple forms of the same enzyme have evolved and are used to effect different functions, how inherited variations in activity are determined, and how genes are developmentally and hormonally regulated.
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