Cell News | Issue 01, 2017 - page 36

Cell News 01/2017
E-cadherin controls EGFR signaling and tissue tension for
polarized epidermal junction and barrier formation
Matthias Rübsam
, Aaron F. Mertz
, Akiharu Kubo
, Placido Pereira
, Eric Dufresne
Valerie Horsley
, Wolfgang Ziegler
, Masayuki Amagai5, Carien Niessen
1 Department of Dermatology, 2 Cologne Excellence Cluster on Cellular Stress Responses in Aging-Associated Diseases (CECAD),
3 Center for Molecular Medicine Cologne, University of Cologne, 50931 Cologne, Germany, 4 Yale University, New Haven, CT
06520, USA, 5 Department of Dermatology, Keio University School of Medicine, Tokyo 160-8582, Japan, 6 Hannover Medical
School, 30625 Hannover, Germany
Presenting author: Placido Pereira
Department of Dermatology and Cologne Excellence Cluster
on Cellular Stress Responses in Aging-Associated Diseases
(CECAD), University of Cologne, 50931 Cologne.
Generation of a barrier in multi-layered epithelia like the
epidermis requires restricted positioning of functional tight
junctions (TJ) to the most suprabasal viable layer. This posi-
tioning necessitates tissue-level polarization of junctions and
the cytoskeleton through unknown mechanisms. Previously,
we showed that epidermal E-cadherin is essential for epi-
dermal TJ barrier function. Using quantitative whole-mount
imaging, genetic ablation, and traction force microscopy, we
find that ubiquitously localized E-cadherin coordinates tissue
polarization of vinculin positive, tension-bearing adherens
junction (AJ) and F-actin organization and allows formation of
an apical ZO1-EGFR-positive TJ network only in the granular
layer 2 (SG2). The SG2 layer itself is highly polarized despite
its flattened appearance with a lateral AJ network reaching
up to a continuous ZO-1 positive apical tight junctional ring.
We find that E-cadherin regulates spatiotemporal positioning
of EGFR receptor during epidermal barrier development at
embryonic day 16.5 and balances EGFR activity critical for in
vitro TJ barrier function. In conclusion, our data link E-cad-
herin-dependent control of suprabasal EGFR activity and the
polarized, tissue-level organization of junctions, tension, and
the cytoskeleton to promote in vivo epidermal barrier forma-
tion. Our results further reveal a mechanistic role for EGFR at
TJs and thereby uncover why EGFR inhibitors compromise skin
barrier function in human cancer patients.
Spindle Morphometrics Throughout Neuronal Differentiation
Sebastian Reusch, Simone Reber
Presenting author: Sebastian Reusch
IRI Life Sciences, Humboldt-Universität zu Berlin
Scaling of the mitotic spindle with cell size is a phenomenon,
which is for example seen in the early developmental stages
of many organisms. Here, it has been shown that the length of
the metaphase spindle varies several-fold among cells, which
is essential in order to segregate chromosomes over different
distances. A similar challenge arises during differentiation,
when cells change size, morphology and function. However, it
is not known whether spindle scaling happens during this pro-
cess and how the tubulin code influences microtubule dynam-
ics during cell fate determination. Experiments for analyzing
mechanisms of spindle length control have been based on in
vitro work such as spindle reconstitution assays using Xenopus
laevis egg extracts. Neuronal differentiation of mouse embry-
onic stem cells can be used as a tool to systematically analyze
spindle morphometrics to further identify mechanisms that
contribute to spindle scaling in vivo. We use live cell spinning
disk and super-resolution microscopy to measure and quantify
parameters of mitotic spindle geometry, which we then relate
to cell size during different time points of neuronal differen-
tiation. To study scaling mechanistically, we will affinity-pu-
rify tubulin over the course of differentiation and analyze
the changes in the tubulin code to get information about
post-translational modifications, isoform expression, microtu-
bule dynamics and protofilament number. Finally, analyzing the
dynamics of microtubule associated proteins by mass spec-
trometry during differentiation can further elute how and why
spindle scaling happens.
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