Origin and Evolution
The mir-2 family originated before the last common ancestor of protostomes, and has been ever since linked to mir-71. The evolution of mir-2 is characterized by successive expansions by duplication events. Since most paralogous microRNAs conserve their function, it has been suggested that mir-2 evolution is dominated by a birth-and-death dynamics driven by random drift.
One mir-2 microRNA in Drosophila, dme-miR-2a-2, is two nucleotides offset with respect to the canonical products of other mir-2 precursors. This is likely to affect the function of that particular microRNA. This functional shift is associated to a change in the genomic distribution of mir-2 sequences in Drosophila. The functional diversification of microRNAs may require breaking the genomic linkage between paralogs, probably to avoid the co-regulation of multiple products by the same regulatory sequences.
In the human parasite Schistosoma mansoni the whole mir-71/mir-2 cluster has been duplicated, and one of the copies is in the sexual chromosome.
Read more about this topic: Mir-2 Micro RNA Precursor
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