Conservation of gene architecture and domains amidst sequence divergence in the hsr[omega] lncRNA gene across the Drosophila genus: an in silico analysis

The developmentally active and cell-stress responsive hsr[omega] locus in Drosophila melanogaster carries two exons, one omega intron, one short translatable open reading frame (ORF[omega]), long stretch of unique tandem repeats and an overlapping mir-4951 near its 3' end. It produces multiple long noncoding RNAs (lncRNAs) using two transcription start and four termination sites. Earlier cytogenetic studies revealed functional conservation of hsr[omega] in several Drosophila species. However, sequence analysis in three species showed poor conservation for ORF[omega], tandem repeat and other regions while the 16 nt at 5' and 60 nt at 3' splice junctions of the omega intron, respectively, were found to be ultra-conserved. The present bioinformatic study using the splice-junction landmarks in D. melanogaster hsr[omega] identified orthologues in publicly available 34 Drosophila species genomes. Each orthologue carries a short ORF[omega], ultra-conserved splice junctions of omega intron, repeat region, conserved 3'-end located at mir-4951, and syntenic neighbours. Multiple copies of conserved nonamer motifs are seen in the tandem repeat region, despite a high variability in the repeat sequences. Intriguingly, only the omega intron sequences in different species show evolutionary relationships matching the general phylogenetic history in the genus. Search in other known insect genomes did not reveal sequence homology although a locus with similar functional properties is suggested in Chironomus and Ceratitis genera. Amidst the high sequence divergence, the conserved organization of exons, ORF[omega] and omega intron in this gene's proximal part and tandem repeats in distal part across the Drosophila genus is remarkable and possibly reflects functional importance of higher order structure of hsr[omega] lncRNAs and the small omega peptide.