Species Distribution
The mir-2 family is specific to protostomes. There are 8 mir-2-related loci in Drosophila melanogaster: mir-2a-1, mir-2a-2, mir-2b-1, mir-2b-2, mir-2c, mir-13a, mir-13b-1 and mir-13b-2. Most other insect genomes host five mir-2 loci although the number varies in other invertebrates. Mir-13 subfamily emerged from mir-2 sequences before the insect radiation.
Although mir-11 and mir-6 have similar sequences to mir-2 microRNAs, they are not evolutionarily related, and therefore should not be considered from the same microRNA family.
Mir-2 hairpin precursor sequences are highly conserved, in particular in their 3' arm in which the first 10 nucleotides are identical to all family members. Functional mir-2 microRNAs come from the 3' arm of the precursors, and most of them have the same Drosha processing point. That means that the seed sequence is virtually the same in all these products, hence, they should target the same transcripts.
Mir-2 microRNAs are organized in a large cluster in most insects. This cluster has typically 5 members of the mir-2 family plus mir-71, an evolutionarily unrelated microRNA. The number of mir-2 sequences differs among invertebrate lineages although they remain tightly clustered in the genome. A notable exception has been observed in Drosophila melanogaster, in which the mir-2 family is organized in two clusters and two single loci. Additionally, mir-7 microRNA has been lost in the Drosophila lineage.
Read more about this topic: Mir-2 Micro RNA Precursor
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