Elucidating The Nanoscale Architecture Of The Desmosome

Authors

• William F. Dean, University of Alabama at Birmingham

Advisor(s)

Alexa Mattheyses

Committee Member(s)

Aaron Lucius
David Schneider
Hui-Ting Lee
Susan Bellis

School

Joint Health Sciences (Interdisciplinary)

Document Type

Dissertation

Department (new version)

Cell Biology

Date of Award

9-9-2024

Abstract

Desmosomes are intercellular anchoring junctions that are crucial for maintaining the mechanical integrity of tissues routinely subjected to large forces, such as epithelia and cardiac muscle. Adhesion in desmosomes is mediated by a specialized class of transmembrane glycoproteins known as the desmosomal cadherins (DCs). Defects in desmosomal adhesion are associated with severe disease of the heart and skin and are frequently linked to mutations in the DCs. It is therefore important to understand the relationship between DC architecture and desmosome function. Accordingly, several groups have attempted to elucidate DC architecture—primarily using electron tomography (ET). However, ET studies of the desmosome are limited in spatial resolution by the inherent flexibility of the DCs, which has led to conflicting results. Consequently, the precise geometric arrangement of the DCs—and the underlying relationship between DC architecture and adhesive function—remain incompletely understood. Excitation-resolved fluorescence polarization microscopy (FPM) is a powerful technique which can be used to measure the order and orientation of fluorescently labeled biomolecules in their native cellular environments. In this dissertation, I leveraged the advantages of FPM by targeting flexible DC domains inaccessible to ET, providing several novel insights into DC architecture and dynamics. I showed that DC ectodomains are significantly more ordered than their intracellular counterparts, reflecting a drastic disparity in architecture between opposing sides of the plasma membrane. Notably, this may account for the unique ability of desmosomes to simultaneously maintain strong intercellular adhesion while also remaining plastic enough to facilitate rapid junctional remodeling in response to cellular cues. Indeed, the disparity between intracellular and extracellular architecture was consistent and broadly conserved across multiple DC isoforms, suggesting it is functionally relevant. Importantly, by statistically correlating FPM measurements with mathematical modeling informed by existing structural data, I was able to discriminate between competing models of DC architecture that could not be distinguished using ET. Finally, I found that DC organization and intercellular adhesive strength increase in a coordinated fashion during desmosome assembly. Taken together, my work has clarified the nanoscale architecture of the DCs, while also shedding light the poorly understood relationship between structure and function in the desmosome.

ProQuest ID

https://proquest.com/docview/3101857817