Two contractile pools of actomyosin distinctly load and tune E-cadherin levels during morphogenesis

Girish R. Kale, Xingbo Yang, Jean-Marc Philippe, Madhav Mani, Pierre-François Lenne, Thomas Lecuit

Posted on: 18 April 2018

Preprint posted on 28 January 2018

Article now published in Nature Communications at http://dx.doi.org/10.1038/s41467-018-07448-8

Fine tuning of adhesion complexes through two distinct pools of actomyosin

Selected by Arnaud Monnard

Categories: biophysics, cell biology

Context

In metazoans, germ-band extension is a morphogenetic process that drives body axis elongation along the anterior-posterior axis¹. The extension is highly dynamic and lasts for about 2.5 hours, but most of the visible changes are concentrated during the first 45 min, called the rapid phase. This extension is thought to be mainly driven by cell intercalation², in which planar polarization of actomyosin and interaction with E-cadherin (E-cad) at adhesion junctions play critical roles in junction remodeling³. Moreover recent work has shown that epithelial junction remodeling is achieved through the action of two pools of non-muscle myosin II (junctional or medial Myo), which are regulated separately^3,4.

Key findings

In this study, Kale et al. looked at the distinct interaction between adhesion complexes and medial or junctional Myo. They initially show that the polarized localization of Vinculin (Vinc) at adhesion complexes is achieved through α-Catenin and that this localization depends on Myo. Next they established a direct correlation between junctional tension and both Vinc/E-cad ratio and junctional Myo by measuring the recoil velocity of Myo and the Vinc/E-cad ratio after laser ablation of the junction. The biophysical measurements were then supplemented with non-invasive mechanical inference to deduce junctional tensions. Subsequently, the authors established that the Vinc/E-cad ratio could be used as a representative measure of the “load on adhesion complexes”.

Figure adapted from Kale et al. : (A) Vinc/E-cad ratio correlates with junctional tension estimated using mechanical inference. (B) Schematic representation of a model of the junction to construct shear stress and the corresponding equation.

Having established the Vinc/E-cad ratio as a meaningful measure of tension, they were then able to address the core focus of the paper: to determine the specific contribution of each pool of Myo (junctional and medial) to adhesion complexes. The authors achieved this by selectively reducing or overexpressing medial Myo. In doing so, they found that medial Myo was responsible for the recruitment of adhesion complexes at the junction globally, whereas junctional Myo was responsible for the planar distribution of adhesion complexes by inducing shear stress on vertical junctions.

Why I chose it

A strength of this study lies in its power to decipher the subcellular physical mechanisms that drive ectodermal convergent-extension movements. By looking at the specific contribution of two different pools of myosin on adhesion complexes, the authors offer us a very detailed and novel perspective on junction dynamics. Moreover, the combination of invasive (laser ablation) and non-invasive (mechanical inference, correlative analysis) measurements in an intact living Drosophila embryo allows the authors to elegantly derive physical properties (tension, stress) of the junction.

Future perspectives

It would be interesting to investigate if these results (the specific contribution of two different pools of Myo to adhesion complexes) could be transposed to different model systems, such as in the fly notum. Finally, and as the authors point out, it remains to be elucidated exactly how the generation of contractile forces by myosin-II activity controls junction remodeling during morphogenesis.

References

Irvine, K. D. & Wieschaus, E. Cell intercalation during Drosophila germband extension and its regulation by pair-rule segmentation genes. Development120,827–841 (1994).
Kong, D., Wolf, F. & Großhans, J. Forces directing germ-band extension in Drosophila embryos. Mech. Dev.144,11–22 (2017).
Rauzi, M., Lenne, P. F. & Lecuit, T. Planar polarized actomyosin contractile flows control epithelial junction remodelling. Nature468,1110–1115 (2010).
Kerridge, S. et al.Modular activation of Rho1 by GPCR signalling imparts polarized myosin II activation during morphogenesis. Nat. Cell Biol.(2016). doi:10.1038/ncb3302