Phylogenetic comparison of the RNA editase ADAR2 genes reveals conservation and diversity in editing site sequence and alternative splicing patterns

Dobromir Slavov
Eleanor Roosevelt Institute
1899 Gaylord Street
Denver, CO 80206-1210
USA
telephone: 303-336-5684
fax: 303-333-8423
email: slavov@eri.uchsc.edu
prestype: Poster
presenter: Dobromir Slavov

Dobromir Slavov and Katheleen Gardiner

ADAR2 (Adenosine Deaminase that Acts on RNA ­2) is one of three known mammalian genes that encode A-to-I RNA editases, enzymes that deaminate specific adenosine (A) residues in specific pre-mRNAs to produce inosines (I). Known substrates of ADAR2 include sites within pre-mRNAs of the ionotropic glutamate receptors, GluR2-GluR7, and the serotonin receptor, 5HT2C. Because the ribosome reads I residues as G residues, and because the edited sites largely occur within coding regions, most of these editing events result in amino acid changes. Editing has been demonstrated to affect protein function, reducing calcium permeability and desensitization recovery times in the glutamate receptors and reducing receptor-G protein coupling in the serotonin receptor. Editing activity is highly regulated; levels are rarely 100% for any of the known pre-mRNA substrates and vary with developmental time and among brain regions. Lack of editing, at least of GluRB, is neonatal lethal. A-to-I RNA editing and the enzymes controlling it thus provide an important mechanism for regulation of neurological development and function by means of regulation of protein function and diversity.

Because of the important biological role of A-to-I editing, it is of interest to examine the evolutionary conservation of ADAR2 regulatory features. We therefore undertook a phylogenetic comparison of the genomic structure, editing and alternative splicing of the ADAR2 genes from human, mouse, chicken, fugu and zebrafish. Here we show that the genomic sequences and RNA secondary structures required for the ADAR2 self-editing within intron 2 are highly conserved among all organisms, more highly conserved than coding exons. Also conserved are general patterns of alternative splicing within the 5’ UTRs. There is, however, diversity in other respects. In chicken and mammalian ADAR2, but not in fish, alternative splicing that likely affects the catalytic domain is observed, although locations and mechanisms differ. Complex 3’ end alternative splicing appears to be mammalian-specific, as does conservation within the 3’UTR.