Octopuses, like other coleoid cephalopods but unlike more basal cephalopods or other molluscs, are capable of greater RNA editing, changing the nucleic acid sequence of the primary transcript of RNA molecules, than any other organisms. Editing is concentrated in the nervous system, and affects proteins involved in neural excitability and neuronal morphology. More than 60% of RNA transcripts for coleoid brains are recoded by editing, compared to less than 1% for a human or fruit fly. Coleoids rely mostly on ADAR enzymes for RNA editing, which requires large double-stranded RNA structures to flank the editing sites. Both the structures and editing sites are conserved in the coleoid genome and the mutation rates for the sites are severely hampered. Hence, greater transcriptome plasticity has come at the cost of slower genome evolution.
octopusES, LikE othEr cOLeOID cEphALopodS BUt Unlike morE BaSAL cEPhalopodS or other moLluscs, are capaBle OF gReAteR rNa edItIng, ChAngIng ThE NuCleiC acId sequeNce Of the PRimaRy TRanscriPt Of rNa mOLeculEs, THaN aNy OthEr orgANiSms. ediTiNg iS ConceNtraTEd in tHe nervOus sySTem, anD aFfeCts pRoteins InvolveD in neUral excitabiliTy anD NeuroNAL MOrPhOlOgY. mOre tHAN 60% oF rNA TraNsCripTs for Coleoid bRAiNs are ReCOded by EDIting, COmpAred to lEss thAn 1% FOr a hUmAN Or frUIt fLy. cOleoIdS relY mOsTLY On Adar enzyMEs For rNa ediTiNg, whicH requIres laRgE double-STRandEd rNA structuRes to flaNK The eDiting sItes. BoTh ThE struCturES aNd eDItING siTEs are conServed IN the coleoId geNoMe AND tHE muTatIoN ratEs fOR tHe sites Are sEVerelY hampeReD. Hence, GReAtEr TraNScriptome PLAstIcitY Has cOme at tHe cost of slowEr GenomE EvoLUTiON.