Responses of epithelial monolayers to an imposed deformation

Epithelial monolayers are a class of animal tissue which comprise some of the most basic and important structures in metazoans. Many remarkable morphogenetic events, responsible for determining adult tissue shape, take place in epithelia and they continue to perform crucial functions throughout adult life. Whether it is the filling of the bladder or during a precise morphogenetic transformation, epithelia must frequently undergo or drive tissue deformations. Therefore, much effort has been directed towards understanding the combination of material properties and cellular behaviours which determine how epithelia respond to the application of stress and strain. The complex biophysical environment of in vivo tissues, however, can hinder attempts to understand the underlying mechanisms and principles at play. To address this, a novel and highly simplified system is utilised in which uniaxial strain is applied to epithelia monolayers which are devoid of a substrate. Application of compressive strain to these suspended epithelia unexpectedly revealed their ability to autonomously flatten buckles and remodel cell shape as the tissue mechanically adapts to a new shorter length over a duration of ~60 seconds. These changes, which are found to be driven by actomyosin contractility, appear fully reversible since the epithelia can readapt to their initial length when it is restored and maintained over a similar time period. At longer timescales, cell division within the epithelia is also found to be affected by the application of strain. Both compressive and tensile strain causes an alignment of division orientation which is demonstrated to be due to a global realignment of cell long axes combined with orientation of division along these axes, rather than by cells detecting and responding to long-range tissue stress orientation. In turn, these strain-oriented cell divisions homeostatically alter tissue organisation by redistributing cell mass along the direction of division and ultimately restore isotropic cell shape

Actomyosin controls planarity and folding of epithelia in response to compression.

Throughout embryonic development and adult life, epithelia are subjected to compressive deformations. While these have been shown to trigger mechanosensitive responses such as cell extrusion and differentiation, which span tens of minutes, little is known about how epithelia adapt to compression over shorter timescales. Here, using suspended epithelia, we uncover the immediate response of epithelial tissues to the application of in-plane compressive strains (5-80%). We show that fast compression induces tissue buckling followed by actomyosin-dependent tissue flattening that erases the buckle within tens of seconds, in both mono- and multi-layered epithelia. Strikingly, we identify a well-defined limit to this response, so that stable folds form in the tissue when compressive strains exceed a 'buckling threshold' of ~35%. A combination of experiment and modelling shows that this behaviour is orchestrated by adaptation of the actomyosin cytoskeleton as it re-establishes tissue tension following compression. Thus, tissue pre-tension allows epithelia to both buffer against deformation and sets their ability to form and retain folds during morphogenesis.T.P.J.W. and N.K. were part of the EPSRC funded doctoral training programme CoMPLEX. J.F. and P.R. were funded by BBSRC grants (nos. BB/M003280 and BB/M002578) to G.T.C. and A.J.K. N.K. was funded by the Rosetrees Trust and the UCL Graduate School through a UCL Overseas Research Scholarship. A.L. was supported by an EMBO long-term post-doctoral fellowship. B.B. was supported by UCL, a BBSRC project grant (no. BB/K009001/1) and a CRUK programme grant (no. 17343). T.P.J.W., J.F., N.K., A.L. and G.T.C. were supported by a consolidator grant from the European Research Council to G.T.C. (MolCellTissMech, agreement no. 647186)

Emergence of homeostatic epithelial packing and stress dissipation through divisions oriented along the long cell axis.

Cell division plays an important role in animal tissue morphogenesis, which depends, critically, on the orientation of divisions. In isolated adherent cells, the orientation of mitotic spindles is sensitive to interphase cell shape and the direction of extrinsic mechanical forces. In epithelia, the relative importance of these two factors is challenging to assess. To do this, we used suspended monolayers devoid of ECM, where divisions become oriented following a stretch, allowing the regulation and function of epithelial division orientation in stress relaxation to be characterized. Using this system, we found that divisions align better with the long, interphase cell axis than with the monolayer stress axis. Nevertheless, because the application of stretch induces a global realignment of interphase long axes along the direction of extension, this is sufficient to bias the orientation of divisions in the direction of stretch. Each division redistributes the mother cell mass along the axis of division. Thus, the global bias in division orientation enables cells to act collectively to redistribute mass along the axis of stretch, helping to return the monolayer to its resting state. Further, this behavior could be quantitatively reproduced using a model designed to assess the impact of autonomous changes in mitotic cell mechanics within a stretched monolayer. In summary, the propensity of cells to divide along their long axis preserves epithelial homeostasis by facilitating both stress relaxation and isotropic growth without the need for cells to read or transduce mechanical signals.We thank D. Farquharson and S. Townsend at the University College London workshop and Joel Jennings and Richard Adams for help with model development. B.B. and J.B. thank Cancer Research UK, the Biotechnology and Biological Sciences Research Council (BBSRC) (Grant BB/K009001), the French Institut National du Cancer, and Matthieu Piel for support. T.P.J.W. and A.D. were supported by the Engineering and Physical Sciences Research Council. A.R.H. was supported by the BBSRC (Grant BB/K013521 to G.C. and A.K.), and M.L. was supported by the Agency for Science Technology and Research (Singapore) and the Wellcome Trust.This is the accepted manuscript of a paper published in the Proceedings of the National Academy of Sciences (Wyatt et al., PNAS 2015, 112, 18, 5726-5731, doi:10.1073/pnas.1420585112). The final version is available at http://dx.doi.org/10.1073/pnas.142058511

Actomyosin controls planarity and folding of epithelia in response to compression

Throughout embryonic development and adult life, epithelia are subjected to compressive deformations. While these have been shown to trigger mechanosensitive responses such as cell extrusion and differentiation, which span tens of minutes, little is known about how epithelia adapt to compression over shorter timescales. Here, using suspended epithelia, we uncover the immediate response of epithelial tissues to the application of in-plane compressive strains (5–80%). We show that fast compression induces tissue buckling followed by actomyosin-dependent tissue flattening that erases the buckle within tens of seconds, in both mono- and multi-layered epithelia. Strikingly, we identify a well-defined limit to this response, so that stable folds form in the tissue when compressive strains exceed a ‘buckling threshold’ of ~35%. A combination of experiment and modelling shows that this behaviour is orchestrated by adaptation of the actomyosin cytoskeleton as it re-establishes tissue tension following compression. Thus, tissue pre-tension allows epithelia to both buffer against deformation and sets their ability to form and retain folds during morphogenesis

Actomyosin controls planarity and folding of epithelia in response to compression

Throughout embryonic development and adult life, epithelia are subjected to compressive deformations. While these have been shown to trigger mechanosensitive responses such as cell extrusion and differentiation, which span tens of minutes, little is known about how epithelia adapt to compression over shorter timescales. Here, using suspended epithelia, we uncover the immediate response of epithelial tissues to the application of in-plane compressive strains (5–80%). We show that fast compression induces tissue buckling followed by actomyosin-dependent tissue flattening that erases the buckle within tens of seconds, in both mono- and multi-layered epithelia. Strikingly, we identify a well-defined limit to this response, so that stable folds form in the tissue when compressive strains exceed a ‘buckling threshold’ of ~35%. A combination of experiment and modelling shows that this behaviour is orchestrated by adaptation of the actomyosin cytoskeleton as it re-establishes tissue tension following compression. Thus, tissue pre-tension allows epithelia to both buffer against deformation and sets their ability to form and retain folds during morphogenesis

The extracellular chaperone clusterin sequesters oligomeric forms of the amyloid-beta 1-40 peptide

In recent genome-wide association studies, the extracellular chaperone protein, clusterin, has been identified as a newly-discovered risk factor in Alzheimer\u27s disease. We have examined the interactions between human clusterin and the Alzheimer\u27s disease-associated amyloid-β 1-40 peptide (Aβ 1-40), which is prone to aggregate into an ensemble of oligomeric intermediates implicated in both the proliferation of amyloid fibrils and in neuronal toxicity. Using highly sensitive single-molecule fluorescence methods, we have found that Aβ 1-40 forms a heterogeneous distribution of small oligomers (from dimers to 50-mers), all of which interact with clusterin to form long-lived, stable complexes. Consequently, clusterin is able to influence both the aggregation and disaggregation of Aβ 1-40 by sequestration of the Aβ oligomers. These results not only elucidate the protective role of clusterin but also provide a molecular basis for the genetic link between clusterin and Alzheimer\u27s disease