Abstracts (first author)
MicroRNA evolution by arms switching and bi-directional transcription
Proper regulation of gene expression and function is in part regulated by non-coding RNAs. One important class of noncoding RNAs, the microRNA, modulates transcript expression activity. To illustrate how microRNAs can contribute to the evolution of animals’ biological regulation, here, I will focus on discussing 1) arms switching and 2) bi-directional transcription of microRNAs located inside the Hox complexes (i.e. miR-10 and miR-iab-4/8). Hox genes are essential transcription factors that establish segmental identity on the head-tail axis of all animals. The miR-10 family is highly conserved in sequence and genomic position among the anterior Hox genes of all bilaterians. By investigating the phenomenon where many miRNAs make functional mature products from one or both arms of the hairpin precursor, it is observed that changes in the miR-10 expression and in the dominant precursor arm from which the mature miRNA sequence derives. Since the predicted messenger RNA targets and inferred function of sequences from opposite arms differ significantly, arm switching provides a fundamental mechanism to evolve the function of a miRNA locus and target gene network. On the other hand, current deep sequencing studies have identified more than 9000 animal microRNAs, but only few loci are known to produce miRNAs from both sense and antisense transcripts. In fly Drosophila melanogaster, the iab-4/iab-8 locus encodes bi-directionally transcribed microRNAs that regulate the function of flanking Hox transcription factors. By expression and functional analyses, it is shown that bi-directional transcription of the miR-iab-4/iab-8 is a conserved Hox regulatory mechanism between fly and the beetle Tribolium castaneum. However, there are key differences in the way Hox genes are being targeted. This allows the understanding of how multiple products from sense and antisense microRNAs target common sites.