Book of Abstracts: Albany 2009
June 16-20 2009
© Adenine Press (2008)
The role of Noncoding RNAs in splicing and neurogenesis
The result of the ENCODE project has indicated that while over 90% of the human genome is transcribed into RNA, protein-coding genes occupy only 2% of the human genome, with the rest of the genome transcribed into RNAs that will not be translated into proteins. It is likely that a significant percentage of such RNAs play functional roles in the cell. A number of non-coding RNAs are highly abundant and have been known for a long time to play critical roles in processes that sustain cellular life, including the ribosomal RNAs, RNase P, tRNAs and snRNAs. A less understood group of non-coding RNAs, the small regulatory RNAs and large mRNA-like non-coding transcripts, seem to play regulatory roles in the cells. While recent studies have shed light on several aspects of the function of small RNAs, the function of large non-coding transcripts has remained almost completely unknown. In our efforts to understand the function of non-coding RNAs, we have selected snRNAs as representatives of housekeeping RNAs for analysis. Also, we have chosen a mRNA-like large RNA in an attempt to understand the mode and scope of the function of this novel class of RNAs in vivo.
Mechanistic and structural similarities between spliceosomal snRNAs and self-splicing group II introns, ribozymes found in both pro- and eukaryotes, have led to the hypothesis that snRNAs are descendents of these ribozymes and thus might play a catalytic role in the spliceosome. To determine if this might indeed be the case, we attempted to determine if the snRNAs can catalyze the chemistry of the splicing reaction. Interestingly, upon incubation with short RNA oligonucleotides, a basepaired complex formed by two of the spliceosomal snRNAs could catalyze a two step reaction chemically identical to group II intron-catalyzed splicing and the second step of the spliceosomal splicing. This reaction was dependent on and occurred in proximity of sequences in the two snRNAs that are known to be involved in splicing. The ability of spliceosomal snRNAs to catalyze splicing in the absence of spliceosomal proteins indicates that despite the presence of ~200 proteins in the spliceosome, the catalytic function of snRNAs has been conserved during the evolution of eukaryotic splicing machines and is likely harnessed during spliceosomal catalysis.
To gain insight into the function of the other major class of non-coding RNAs, the regulatory RNAs, we analyzed the cellular function of a pre-mRNA-like large RNA by first determining its tissue expression pattern. Interestingly, it showed a highly specific expression pattern which was largely restricted to neuronal tissues. Overexpression of the RNA in cell types as diverse as myoblasts and fibroblasts blocked their normal differentiation pathway, and instead led to their differentiation into neurons. This surprising result suggested that this RNA may play a key regulatory role in neuronal differentiation and reprogramming of cellular fate and proves the power of RNAs as cellular regulators.
Center for RNA Molecular Biology