%0 Journal Article
%T Vive la diff¨¦rence: biogenesis and evolution of microRNAs in plants and animals
%A Michael J Axtell
%A Jakub O Westholm
%A Eric C Lai
%J Genome Biology
%D 2011
%I BioMed Central
%R 10.1186/gb-2011-12-4-221
%X The first microRNAs (miRNAs) to be discovered, lin-4 and let-7, were found to be regulators of Caenorhabditis elegans development [1-3], and they established a paradigm for eukaryotic gene regulation in which short hairpins generate RNAs of approximately 22 nucleotides (nt) that repress specific target mRNAs. miRNAs have proved to be pervasive in both animals [4-6] and plants [7,8], acting as sequence-specific guides for target recognition [9,10]. Several thousand miRNAs have now been found in dozens of plants and animals [11]. Moreover, the biogenesis and activity of miRNAs are strongly related to those of small interfering RNAs (siRNAs) that mediate RNA interference, another ancient mechanism for post-transcriptional gene silencing [12].Although miRNAs mediate diverse aspects of development and physiology in both plants and animals [13,14], there are substantial differences between them. For example, the loci that produce miRNAs have distinct genomic arrangements in each kingdom. Furthermore, miRNAs are excised from precursor transcripts by different pathways in the two kingdoms, and in different subcellular compartments. Once made, plant and animal miRNAs have vastly different suites of direct targets; the number of direct targets of a given animal miRNA generally exceeds that of a given plant miRNA by at least an order of magnitude [15]. Herein, we focus on how these differences contribute to, and are the result of, distinct evolutionary characteristics of miRNAs in the two kingdoms. We also highlight many commonalities between the respective systems that may reflect a shared evolutionary heritage or convergent strategies for handling and metabolizing double-stranded RNAs.What is a miRNA? Answering this question is not a simple task, as no single definition clearly and specifically encompasses all miRNAs. Although practical guides for miRNA annotation in plants and animals exist [16,17], not all loci reported in the miRBase registry [18] have been annotated to t
%U http://genomebiology.com/2011/12/4/221