Comparative Expression Dynamics of Intergenic Long Noncoding RNAs in the Genus Drosophila.

Thousands of long noncoding RNAs (IncRNAs) have been annotated in eukaryotic genomes, but comparative transcriptomic approaches are necessary to understand their biological impact and evolution. To facilitate such comparative studies in Drosophila, we identified and characterized IncRNAs in a second Drosophilid the evolutionary model Drosophila pseudoobscura. Using RNA-Seq and computational filtering of protein-coding potential, we identified 1,589 intergenic IncRNA loci in D. pseudoobscura. We surveyed multiple sex-specific developmental stages and found, like in Drosophila melanogaster, increasingly prolific IncRNA expression through male development and an overrepresentation of IncRNAs in the testes. Other trends seen in D. melanogaster, like reduced pupal expression, were not observed. Nonrandom distributions of female-biased and non-testis-specific male-biased IncRNAs between the X chromosome and autosomes are consistent with selection-based models of gene trafficking to optimize genomic location of sex-biased genes. The numerous testis-specific IncRNAs, however, are randomly distributed between the X and autosomes, and we cannot reject the hypothesis that many of these are likely to be spurious transcripts. Finally, using annotated IncRNAs in both species, we identified 134 putative IncRNA homologs between D. pseudoobscura and D. melanogasterand find that many have conserved developmental expression dynamics, making them ideal candidates for future functional analyses.