Figure 1.

History of the miR-9 gene family. (A) Phylogenetic tree showing the evolutionary relationships between different model species and the composition of the miR-9 gene family in their respective genomes. The preferred microRNA strand is represented in red, while the non-preferred (or “star”) is represented in black. No miR-9 gene has been recovered so far from genomes of cnidarian species, such as the sea anemone or hydra, suggesting that the emergence of a miR-9 gene occurred at the transition towards triploblasty. At the origin of jawed vertebrates, two rounds of whole genome duplications (WGD) have occurred. An additional WGD occurred in the teleost lineage. These duplication events likely account for the presence of multiple miR-9 genes in vertebrates. Eutherian mammals lost one class of miR-9 genes (corresponding to miR-9-4, also called miR-9b). (B) Alignment of pre-miR-9 sequences from Drosophila and human. Sequences, names and reference numbers were retrieved from miRBase.¹ Nucleotides highlighted in bold correspond to the two microRNA strands, with the preferred strand in red, and the non-preferred one in black.