A Novel Brain-specific Box C/D Small Nucleolar RNA Processed from Tandemly Repeated Introns of a Noncoding RNA Gene in Rats

Jérôme Cavaillé, Patrice Vitali, Eugenia Basyuk, Alexander Hüttenhofer, Jean-Pierre Bachellerie
2001 Journal of Biological Chemistry  
Antisense box C/D small nucleolar RNAs (snoRNAs) guide the 2-O-ribose methylations of eukaryotic rRNAs and small nuclear RNAs (snRNAs) through formation of a specific base pairing at each RNA methylation site. By analysis of a box C/D snoRNA cDNA library constructed from rat brain RNAs, we have identified a novel box C/D snoRNA, RBII-36, which is devoid of complementarity to rRNA or an snRNA and exhibits a brain-specific expression pattern. It is uniformly expressed in all major areas of adult
more » ... jor areas of adult rat brain (except for choroid plexus) and throughout rat brain ontogeny but exclusively detected in neurons in which it exhibits a nucleolar localization. In vertebrates, known methylation guide snoRNAs are intron-encoded and processed from transcripts of housekeeping genes. In contrast, RBII-36 snoRNA is intron-encoded in a gene preferentially expressed in the rat central nervous system and not in proliferating cells. Remarkably, this host gene, which encodes a previously reported noncoding RNA, Bsr, spans tandemly repeated 0.9-kilobase units including the snoRNA-containing intron. The novel brain-specific snoRNA appears to result not only from processing of the debranched lariat but also from endonucleolytic cleavages of unspliced Bsr RNA (i.e. an alternative splicing-independent pathway unreported so far for mammalian intronic snoRNAs). Sequences homologous to RBII-36 snoRNA were exclusively detected in the Rattus genus of rodents, suggesting a very recent origin of this brain-specific snoRNA. In eukaryotic cells, ribosome biogenesis takes place mainly in the nucleolus, through a series of intricate steps including (i) rDNA transcription by the cognate RNA polymerase I, (ii) processing of the pre-rRNA transcript by endo-and exonucleases and covalent modification of a subset of pre-rRNA nucleotides, (iii) packaging of pre-rRNA by ribosomal proteins, and (iv) cytoplasmic export of ribosomal subunits. Pre-rRNA mat-
doi:10.1074/jbc.m103544200 pmid:11346658 fatcat:aetihcpi2vgmdnht7wadivigsq