Unveiling the functional and evolutionary landscape of RNA editing in chicken using genomics and transcriptomics

The evolutionary and functional features of RNA editing are well studied in mammals,cephalopods,and insects,but not in birds.Here,we integrated transcriptomic and whole-genomic analyses to exhaustively characterize the expansive repertoire of adenosine-to-inosine(A-to-I)RNA editing sites(RESs)in the chicken.In addition,we investigated the evolutionary status of the chicken editome as a potential mechanism of domestication.We detected the lowest editing level in the liver of chickens,compared to muscles in humans,and found higher editing activity and specificity in the brain than in non-neural tissues,consistent with the brain’s functional complexity.To a certain extent,specific editing activity may account for the specific functions of tissues.Our results also revealed that sequences critical to RES secondary structures remained conserved within avian evolution.Furthermore,the RNA editome was shaped by purifying selection during chicken domestication and most RESs may have served as a selection pool for a few functional RESs involved in chicken domestication,including evolution of nervous and immune systems.Regulation of RNA editing in chickens by adenosine deaminase acting on RNA(ADAR)enzymes may be affected by non-ADAR factors whose expression levels changed widely after ADAR knockdown.Collectively,we provide comprehensive lists of candidate RESs and non-ADAR-editing regulators in the chicken,thus contributing to our current understanding of the functions and evolution of RNA editing in animals.

The RNA editome of Macaca mulatta and functional characterization of RNA editing in mitochondria

RNA editing was first discovered in mitochondrial RNA molecular. However, whether adenosine-toinosine(A-to-I) RNA editing has functions in nuclear genes involved in mitochondria remains elusive.Here, we retrieved 707,246 A-to-I RNA editing sites in Macaca mulatta leveraging massive transcriptomes of 30 different tissues and genomes of nine tissues, together with the reported data, and found that A-to-I RNA editing occurred frequently in nuclear genes that have functions in mitochondria. The mitochondrial structure, the level of ATP production, and the expression of some key genes involved in mitochondrial function were dysregulated after knocking down the expression of ADAR1 and ADAR2, the key genes encoding the enzyme responsible for RNA editing. When investigating dynamic changes of RNA editing during brain development, an amino-acid-changing RNA editing site(I234/V) in MFN1, a mediator of mitochondrial fusion, was identified to be significantly correlated with age, and could influence the function of MFN1. When studying transcriptomes of brain disorder, we found that dysregulated RNA editing sites in autism were also enriched within genes having mitochondrial functions. These data indicated that RNA editing had a significant function in mitochondria via their influence on nuclear genes.

Integrative analyses of RNA editing,alternative splicing,and expression of young genes in human brain transcriptome by deep RNA sequencing

Next-generation RNA sequencing has been successfully used for identification of transcript assembly,evaluation of gene expression levels,and detection of post-transcriptional modifications.Despite these large-scale studies,additional comprehensive RNA-seq data from different subregions of the human brain are required to fully evaluate the evolutionary patterns experienced by the human brain transcriptome.Here,we provide a total of 6.5 billion RNA-seq reads fromdifferent subregions of the human brain.A significant correlation was observed between the levels of alternative splicing and RNA editing,which might be explained by a competition between the molecularmachineries responsible for the splicing and editing of RNA.Younghuman protein-coding genesdemonstrate biased expression to the neocortical and non-neocortical regions during evolution on the lineage leading to humans.Wealso found that a significantly greater number of young human protein-coding genes are expressed in the putamen,a tissue that was also observed to have the highest level of RNA-editing activity.The putamen,which previously received little attention,plays an important role in cognitive ability,and our data suggest a potential contribution of the putamen to human evolution.