J RNAi Gene Silencing (2015), 11, 507-514
Published online: 16 February 2015
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Properties and kinetics of microRNA regulation through canonical seed sites
Jerry S Chen 1,3, Arra C Revilla 3, Michael Guerrero 3, Abygail M Gumbayan 3 and Robert W Zeller 1,2,3,*
1 Computational Science Research Center
2 Center for Applied and Experimental Genomics, 3Department of Biology, University of California, 5500 Campanile Drive, San Diego, CA 92182, USA
*Correspondence to: Robert Zeller, Email: firstname.lastname@example.org, Tel: +619 594 6458, Fax: +619 594 5676
Received: 26 November 2014, Revised: 22 January 2015, Accepted: 16 February 2015
© Copyright The Author(s). First Published by Library Publishing Media. This is an open access article, published under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0). This license permits non-commercial use, distribution and reproduction of the article, provided the original work is appropriately acknowledged with correct citation details.
MicroRNAs are a fundamental class of small RNAs involved in post-transcriptional gene regulation; however, the mechanism by which microRNAs regulate their gene targets in animals remains poorly understood. Practically, a mechanistic understanding of microRNA binding and regulation is crucial for the rational design of microRNA-based vectors for RNA interference. In this report, we focus on the largest known class of microRNA targets, the canonical seed targets, and explore the factors involved in modulating target downregulation in vivo at the protein level. Using an in vivo sensor assay in the ascidian Ciona intestinalis, we quantify miR-124-mediated downregulation of 38 canonical seed targets cloned from the Ciona genome as well as 10 control non-targets. Supporting previous findings, we observed that the seed type and number of seed sites are correlated with downregulation. However, up to a 50% variation in downregulation levels was observed for targets within the same seed class, indicating a role of non-seed factors in modulating downregulation. Although we did not observe a significant correlation of previously reported non-seed determinants with downregulation levels at saturation in our assay, our data suggest that two previously identified factors, secondary structure and 3’end complementarity, may play a role in the initial kinetics of microRNA-target binding. Importantly, using different concentrations of miR-124 we show that dose-dependent target downregulation profiles follow Michaelis-Menten kinetics. In summary, our findings emphasize the importance of non-seed factors as well as the importance of cellular concentrations of microRNAs relative to their targets when studying the mechanisms of endogenous microRNA regulation.
KEYWORDS: microRNA, miRNA targets, canonical target, seed site, Michaelis-Menten