PRIMARY STRUCTURE, NEURAL-SPECIFIC EXPRESSION, AND DENDRITIC LOCATION OF HUMAN BC200 RNA

Primate BC200 RNA is a 200-nucleotide-long, nontranslatable RNA that is prevalently expressed in the nervous system. We have determined the primary structure of human BC200 RNA, using cDNA cloning and PCR techniques. BC200 RNA can be subdivided into three structural domains. The 5' region is homologous to Alu repetitive elements that are found in high copy numbers in primate genomes. The central part of BC200 RNA is characterized by a high percentage of A-residues, with a few interspersed other nucleotides. The 3' sequence is unique to BC200 RNA and shows no apparent similarity with known human DNA sequences. Sequence similarity with rodent BC1 RNA is limited to several short elements, and BC1/BC200 sequence comparisons indicate that the two genes have evolved via separate phylogenetic routes. Probes directed against the 3' unique part of BC200 RNA detected a single band corresponding to approximately 200 nucleotides on RNA blots. This band was identified only with RNA isolated from human brain, not with RNA from non-neural organs such as lung or kidney. In situ hybridization to selected areas of the human nervous system showed that BC200 RNA is expressed by a subpopulation of neurons that is analogous to the BC1 RNA-expressing subset of neurons in the corresponding areas of the rat nervous system. Moreover, like rat BC1 RNA, human BC200 RNA was localized to dendrite-rich neuropil areas, for example, in the inner plexiform layer of the retina. These results indicate that BC1 RNA and BC200 RNA, although of different evolutionary pedigree, may play analogous functional roles, in rodents and primates, respectively, in somatodendritic domains of nerve cells.