Genome Sequence of the Pea Aphid Acyrthosiphon pisum
miRNA biogenesis is initiated in the nucleus by the Drosha-Pasha complex, resulting in precursors of around 60–70 nucleotides named pre-miRNAs. Pre-miRNAs are exported from the nucleus to the cytoplasm by Exportin-5. In the cytoplasm, Dicer-1 and its cofactor Loquacious (Loq) cleave these pre-miRNAs to produce mature miRNA duplexes. A duplex is then separated and one strand is selected as the mature miRNA whereas the other strand is degraded. This mature miRNA is integrated into the multiprotein RISC complex, which includes the key protein Argonaute 1 (Ago1). Integration of miRNAs into RISC will lead to the inhibition of targeted genes either by the degradation of the target mRNA or by the inhibition of its translation. All components of the miRNA pathway have been identified in the pea aphid. Shown are the number of homologs in A. pisum (Ap) as well as Drosophila melanogaster (Dm), Anopheles gambiae (Ag), Tribolium castaneum (Tc), and Apis mellifera (Am). While all these genes are monogenic in these insect species, the pea aphid possesses two copies of dicer-1, loquacious, and argonaute-1 and four copies of pasha (red font). The second loquacious copy is degraded and probably corresponds to a pseudogene.