Nova Alternative RNA Splicing Targets Neuronal Proteins

A new study describes a method to purify protein-RNA complexes from mouse brain that allows researchers to identify an array of RNA molecules regulated by Nova, an RNA-binding protein that regulates alternative RNA splicing.

Nova proteins are neuron-specific antigens targeted in paraneoplastic opsoclonus myoclonus ataxia (POMA), an autoimmune neurologic disease characterized by abnormal motor inhibition. Nova proteins regulate neuronal pre-messenger RNA splicing by directly binding to RNA.

RNA splicing is an essential, precisely regulated post-transcriptional process that occurs prior to mRNA translation. A gene is first transcribed into a pre-messenger RNA (pre-mRNA), which is a copy of the genomic DNA containing intronic regions destined to be removed during pre-mRNA processing (RNA splicing), as well as exonic sequences that are retained within the mature mRNA. During RNA splicing, exons can either be retained in the mature message or targeted for removal in different combinations to create a diverse array of mRNAs from a single pre-mRNA, a process referred to as alternative RNA splicing.

Alternative splice events that affect the protein coding region of the mRNA will give rise to proteins that differ in their sequence and therefore in their activities. Alternative splicing within the noncoding regions of the RNA can result in changes in regulatory elements such as translation enhancers or RNA stability domains, which may have a dramatic effect on the level of protein expression.

Investigators at Rockefeller University (New York, NY, USA; www.rockefeller.edu) employed a technique called cross-linking and immunoprecipitation (CLIP) to chemically bond the NOVA protein to its RNA targets. In a novel adaptation of this method, they applied it to intact mouse brains in order to trap the protein-RNA complexes as they are in situ. In the November 14, 2003, issue of Science, they reported that 34 transcripts were identified multiple times by Nova CLIP. Three-quarters of these encoded proteins functioned at the neuronal synapse, and one-third were involved in neuronal inhibition.

"Looking at these targets as a group, they have a tremendous biological coherence to them,” observed senior author Dr. Robert B. Darnell, a Howard Hughes Medical Institute investigator at Rockefeller University. "Almost 70% of them are RNAs that have something to do with the neuronal synapse. One-third of the Nova synaptic RNA targets encode proteins involved in inhibiting neuronal function. Regulating neuronal inhibition plays a key role in the balance-controlling nervous system function normally as well as in neurological disorders such as epilepsy.”



Related Links:
Rockefeller University