PhD Exit Seminar – Debanjan Barua (Winklbauer Lab)

Cell contact and tissue architecture in the Xenopus laevis gastrula

Cell-cell contact and tissue architecture in the multilayered tissues of the Xenopus laevis gastrula is a complex and fascinating topic. These tissues must be flexible in order to allow for dynamic cell rearrangements while maintaining tissue integrity. Here, I describe the layout of these tissues by exploring the landscape of adhesive cell-cell contacts, describing the mechanics of interstitial channels between cells, and analyzing the effect of tissue-tissue interactions on tissue cohesion. I use transmission electron microscopy (TEM) to analyze the ultrastructure of these multilayered tissues. I find that modulation of adhesion is reflected structurally at cell-cell contacts which span a wide range of intercellular separation distances. Altogether, cell-cell adhesion in the Xenopus gastrula can be categorized into two general types: narrow contacts mediated by Syndecan-4 and C-cadherin along which cells are 0-50nm apart, and wider 50-1000nm contacts mediated by the glycocalyx. These tissues are also permeated by a network of channels that appear in TEM sections as interstitial gaps. I characterize this interstitial space in the ectoderm by examining the geometry and mechanics of gaps at three-cell junctions. From this, I generate a model of interstitial gap mechanics which suggests that gaps can be formed by the insertion of a fluid-like extracellular matrix material at three-cell junctions such that cell adhesion is locally disrupted and a small cortical tension difference between cell-cell contacts and the free cell surface at gaps of 0.003 mJ/m2 is generated. Lastly, to examine the effects of tissue-tissue interactions on tissue cohesion, I examined Eph/ephrin signaling at the ectoderm-mesoderm boundary. I show that the mesoderm is more sensitive to Eph/ephrin signaling than the ectoderm and that asymmetrical expression of a few Eph receptors and ephrin ligands establishes a mirror on the ectodermal side of the cleft which allows the mesoderm to be weakly self-adhesive and also weakly adhesive to the ectoderm. Integrating these concepts together, I propose that the flexible architecture of these multilayered tissues is maintained by a balance of adhesive contacts and non-adhesive gaps that can be regulated by tissue-tissue interactions.

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Join Zoom Meeting

Thursday, February 18th, 2021

https://utoronto.zoom.us/j/89779977983

Meeting ID: 897 7997 7983