Publication Date:
2012-07-31
Description:
The recent discovery of microRNAs (miRNAs) in unicellular eukaryotes, including miRNAs known previously only from animals or plants, implies that miRNAs have a deep evolutionary history among eukaryotes. This contrasts with the prevailing view that miRNAs evolved convergently in animals and plants. We re-evaluate the evidence and find that none of the 73 plant and animal miRNAs described from protists meet the required criteria for miRNA annotation and, by implication, animals and plants did not acquire any of their respective miRNA genes from the crown ancestor of eukaryotes. Furthermore, of the 159 novel miRNAs previously identified among the seven species of unicellular protists examined, only 28 from the algae Ectocarpus and Chlamydomonas , meet the criteria for miRNA annotation. Therefore, at present only five groups of eukaryotes are known to possess miRNAs, indicating that miRNAs have evolved independently within eukaryotes through exaptation of their shared inherited RNAi machinery. Only five eukaryotic clades (plants, green algae, brown algae, demosponges, and eumetazoans) are currently known to possess microRNAs, with each clade evolving their own unique repertoire. The only conserved element in microRNA biogenesis is the multi-domain protein DICER and provides another example of molecular exaptation.
Print ISSN:
0265-9247
Electronic ISSN:
1521-1878
Topics:
Biology
,
Medicine
