On the role of miRNAs in adult tissues

We are thrilled to share a new paper describing a novel approach to interfere with global microRNA activity in cells and in living animals without affecting miRNA biogenesis or miRNA abundance. You can read the paper on eLife or on bioRxiv, where it was initially posted as a preprint.

At the core of this work is a peptide (T6B) previously generated by Gunter Meister and Tom Tuschl that binds to Argonaute proteins and prevents the assembly of a functional miRISC complex, thus effectively blocking miRNA-mediated gene repression without impairing miRNA biogenesis.

Schematics of how T6B works

To explore the consequences of miRNA-inhibition in vivo, we have generated a novel genetically engineered mouse strain that expresses the T6B peptide fused to YFP in a doxycycline-inducible manner. By crossing it with an appropriate rtTA expressing strain it is possible to block miRNA function in a tissue-restricted and temporally controlled manner.

T6B-YFP expression in a panel of tissues and in embryos

The effect is fully reversible, and miRNA biogenesis (or endogenous siRNA function) are not affected. The entity of de-repression of predicted miRNA targets is roughly proportional to the corresponding miRNA family abundance.

Bubble plot showing global inhibition of miRNA function in MEFs

Each “bubble” in the plot above is a set of predicted targets of a miRNA family. On the x axis we plotted the average log2 fold change compared to the background(reported as z-score) and on the y-axis is the miRNA family abundance. Using this novel mouse strain we show that although miRNA-mediated repression is required during embryonic development, in many adult tissues it seems largely dispensable under homeostatic conditions, and becomes essential only in after acute damage and during regeneration. 

A notable exception is represented by the skeletal muscle and the heart, where even under physiologic conditions T6B induction results in tissue degeneration and death.

Effect of T6B expression on muscle and heart

We have a ton of follow-up experiments planned and we hope our colleagues interested in the biology of miRNAs will find it useful. As always, the mouse strain will be freely available through @jacksonlab as soon as we have completed the donation process. 

This work was the result of a collaborative effort between our lab, the Thompson lab, the @KevinHaigisLab lab, the Tuschl lab, the @dbetel lab, the @VidigalJoana lab, and the @MeisterLab

Dr. Gaspare La Rocca deserves a special mention as he was the main driver of this project. He came up with the idea, performed—together with Bryan King—most of the key experiments, and persisted through many ups and downs during the past few years. 

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