Epigenetics in Health and Disease (Chris Mathews' Library) by Igor Kovalchuk Ph.D. MD & Olga Kovalchuk Ph.D. MD

Author:Igor Kovalchuk, Ph.D., MD & Olga Kovalchuk, Ph.D., MD
Language: eng
Format: epub
Publisher: FT Press
Published: 2012-06-13T16:00:00+00:00

Evolutionary conservation of miRNAs

According to Release 16 of the miRNA Registry Database (www.mirbase.org), there are 916 miRNAs from plants including Arabidopsis, rice (Oryza sativa), corn (Zea mays), poplar (Populus trichocarpa), as well as many others. miRNA genes are conserved among many plants. The fact that miRNAs are conserved in rice and Arabidopsis suggests that miRNA regulatory mechanism has developed before the divergence of monocot and dicot plants (reviewed in Yang et al., 2007). miR166 targets class III homeodomain-leucine zipper (HD-ZIP III) transcription factors in various plants, providing further evidence that miRNA-based regulation is one of the oldest mechanisms of posttranscriptional regulation in plants. The expression of flowering plant miRNAs—such as miR160, miR390, and miR160—were detected in gymnosperms, fern, and moss, suggesting that many plant miRNAs have remained mostly unchanged since before the emergence of flowering plants (reviewed in Yang et al., 2007). Analysis of hairpin structures of miRNAs belonging to the same gene family showed a high degree of conservation among the analyzed plants species (Yang et al., 2007). In fact, more than eight families of miRNA genes have apparently appeared before the emergence of seed plants. At the same time, most of the other miRNA families exhibit a substantial degree of divergence between species, possibly allowing to them regulate common processes that became specialized in a given plant species. This diversity is also reflected in that some of the miRNAs specific to Arabidopsis have appeared recently and are rather unique (nonconserved) for dictos. According to one of the models, miRNA genes appeared as a result of the transcription of genes that underwent inverted duplication. “Read through” transcription of such genes results in the formation of hairpin structures that are recognized by DCL1 as a pri-miRNA.

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