Morphogen-like properties of small RNA gradients: A new paradigm for the role of small RNAs in developmental biology

Project Information

MorphGrad

Grant agreement ID: 709293

DOI

10.3030/709293

Project closed

EC signature date 16 December 2016

Start date 1 March 2017

End date 28 February 2019

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 159 460,80

EU contribution

€ 159 460,80

Coordinated by

EBERHARD KARLS UNIVERSITAET TUEBINGEN
Germany

Periodic Reporting for period 1 - MorphGrad (Morphogen-like properties of small RNA gradients: A new paradigm for the role of small RNAs in developmental biology)

Reporting period: 2017-03-01 to 2019-02-28

Summary of the context and overall objectives of the project

This fellowship investigated the mechanisms by which small RNAs function as novel intercellular messengers that provide important developmental signals. Coordinated development of multicellular organisms depends on the ability of cells to assess their relative positions within the growing organism. This is achieved through intercellular communication, commonly based on the production and perception of mobile signaling molecules. In addition to the well-established peptide ligands, transcription factors, and hormones, small RNAs have emerged as a new class of mobile instructive signals in development. Small RNAs possess intrinsic properties that make them particularly well suited to drive developmental change. These include a high degree of specificity, a direct and rapid mode of action, and the ability to confer sensitivity and robustness onto gene regulatory networks. One additional obvious advantage of employing mobile small RNAs in development is that they represent a distinct class of signaling molecules whose movement can, in principle, be regulated independently from that of other mobile signals. However, despite its central importance, an understanding of how the cell-to-cell movement of small RNAs is governed has been lacking. This fellowship investigated the mechanisms by which small RNAs move from cell to cell and function as novel intercellular messengers that provide important developmental signals.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

To investigate the process of small RNA mobility, we took advantage of a so-called miRNA sensor system. Here, an artificial miRNA is expressed from tissue-specific promoters and assayed for its capacity to silence a ubiquitously-expressed, cell-autonomous, easy-to-score reporter. Our observations using this system reveal a new paradigm for how miRNAs function as mobile signals. We showed that small RNA mobility is precisely regulated through a gating mechanism that acts independent of mechanisms controlling protein movement, identifying the small RNA as the mobile unit. The gating of small RNA mobility occurs at defined cell-cell interfaces. This generates directional movement between neighbouring cells that generates selectivity in long-distance signalling, and helps safeguard functional domains within the dynamic plant stem cell niches while mitigating a ‘signalling gridlock’ in contexts where developmental patterning events occur in close spatial and temporal vicinity.

To identify the gate-keepers regulating cell-to-cell small RNA mobility, we used the same sensor system in an unbiased forward genetic screen. In contrast to earlier screens, no a priori assumption was made as to whether regulators of miRNA mobility act by facilitating or confining movement. This screen design may have been invaluable, as we identified several mutants in putative facilitators and restrictors of miRNA mobility. The screen has been completed, but we are still in the process of identifying the causative gene lesions. Once completed this will generate another important publication, as indeed factors regulating small RNA mobility can be used to modulate development and tune abiotic and biotic stress responses across the plant.

Peer reviewed publications:
D.S. Skopelitis, K. Hill*, S. Klesen, C.F. Marco, P. von Born, D.H. Chitwood, M.C.P.Timmermans (2018). Gating of miRNA movement at defined cell-cell interfaces governs their impact as positional signals. Nature Communications 9, 3107-3117. *Equal contribution.

Conference presentations:
Talk: Kristine Hill (2018) Gating of miRNA movement at defined cell-cell interfaces governs their impact as positional signals. 29th International Conference on Arabidopsis Research Turku, Finland.
Talk: Kristine Hill (2017) Regulation of cell-to-cell miRNA mobility. Intercellular communication in development and disease, EMBO meeting, Berlin, Germany
Poster: Kristine Hill, Damianos Skopelitis, Simon Klesen, & Marja Timmermans (2018) Regulation of cell-to-cell miRNA mobility. RegioPlantScience Meeting, ZMPB, Tübingen, Germany.
Poster: Kristine Hill, Damianos Skopelitis, Simon Klesen, & Marja Timmermans (2017) Regulation of cell-to-cell miRNA mobility. FASEB Mechanisms in Plant Development, Saxons River, Vt, US.

In addition, M. Timmermans presented findings from this project at a number of national and international conferences and seminars.

Talk: Kristine Hill (2017) Regulation of cell-to-cell miRNA mobility. Intercellular communication in development and disease, EMBO meeting, Berlin, Germany
Poster: Kristine Hill, Damianos Skopelitis, Simon Klesen, & Marja Timmermans (2018) Regulation of cell-to-cell miRNA mobility. RegioPlantScience Meeting, ZMPB, Tübingen, Germany.
Poster: Kristine Hill, Damianos Skopelitis, Simon Klesen, & Marja Timmermans (2017) Regulation of cell-to-cell miRNA mobility. FASEB Mechanisms in Plant Development, Saxons River, Vt, US.

In addition, M. Timmermans presented findings from this project at a number of national and international conferences and seminars.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The movement of small RNAs is fundamental to plant development, growth, and survival. Besides providing positional information in development, mobile small RNAs are critical for protection against the damaging effects of transposons, and in coordinating abiotic and biotic stress responses across the plant. Our results show how the movement of miRNAs is a carefully regulated. Together with outcomes from the screen, this knowledge can be used to modulate development and tune abiotic and biotic stress responses across the plant, e.g. to protect plants against stress from drought or nutrient deprivation. For further information, see Skopelitis, Hill, et al., 2018. Nat Commun. 9, 3107-3117.

Schematic representation of polarised gate-keepers regulating the cell-to-cell movement of miRNAs.