---
OA_place: repository
_id: '1403'
abstract:
- lang: eng
  text: A variety of developmental and disease related processes depend on epithelial
    cell sheet spreading. In order to gain insight into the biophysical mechanism(s)
    underlying the tissue morphogenesis we studied the spreading of an epithelium
    during the early development of the zebrafish embryo. In zebrafish epiboly the
    enveloping cell layer (EVL), a simple squamous epithelium, spreads over the yolk
    cell to completely engulf it at the end of gastrulation. Previous studies have
    proposed that an actomyosin ring forming within the yolk syncytial layer (YSL)
    acts as purse string that through constriction along its circumference pulls on
    the margin of the EVL. Direct biophysical evidence for this hypothesis has however
    been missing. The aim of the thesis was to understand how the actomyosin ring
    may generate pulling forces onto the EVL and what cellular mechanism(s) may facilitate
    the spreading of the epithelium. Using laser ablation to measure cortical tension
    within the actomyosin ring we found an anisotropic tension distribution, which
    was highest along the circumference of the ring. However the low degree of anisotropy
    was incompatible with the actomyosin ring functioning as a purse string only.
    Additionally, we observed retrograde cortical flow from vegetal parts of the ring
    into the EVL margin. Interpreting the experimental data using a theoretical distribution
    that models  the tissues as active viscous gels led us to proposen that the actomyosin
    ring has a twofold contribution to EVL epiboly. It not only acts as a purse string
    through constriction along its circumference, but in addition constriction along
    the width of the ring generates pulling forces through friction-resisted cortical
    flow. Moreover, when rendering the purse string mechanism unproductive EVL epiboly
    proceeded normally indicating that the flow-friction mechanism is sufficient to
    drive the process. Aiming to understand what cellular mechanism(s) may facilitate
    the spreading of the epithelium we found that tension-oriented EVL cell divisions
    limit tissue anisotropy by releasing tension along the division axis and promote
    epithelial spreading. Notably, EVL cells undergo ectopic cell fusion in conditions
    in which oriented-cell division is impaired or the epithelium is mechanically
    challenged. Taken together our study of EVL epiboly suggests a novel mechanism
    of force generation for actomyosin rings through friction-resisted cortical flow
    and highlights the importance of tension-oriented cell divisions in epithelial
    morphogenesis.
acknowledged_ssus:
- _id: SSU
alternative_title:
- IST Austria Thesis
article_processing_charge: No
author:
- first_name: Martin
  full_name: Behrndt, Martin
  id: 3ECECA3A-F248-11E8-B48F-1D18A9856A87
  last_name: Behrndt
citation:
  ama: Behrndt M. Forces driving epithelial spreading in zebrafish epiboly. 2014.
  apa: Behrndt, M. (2014). <i>Forces driving epithelial spreading in zebrafish epiboly</i>.
    IST Austria.
  chicago: Behrndt, Martin. “Forces Driving Epithelial Spreading in Zebrafish Epiboly.”
    IST Austria, 2014.
  ieee: M. Behrndt, “Forces driving epithelial spreading in zebrafish epiboly,” IST
    Austria, 2014.
  ista: Behrndt M. 2014. Forces driving epithelial spreading in zebrafish epiboly.
    IST Austria.
  mla: Behrndt, Martin. <i>Forces Driving Epithelial Spreading in Zebrafish Epiboly</i>.
    IST Austria, 2014.
  short: M. Behrndt, Forces Driving Epithelial Spreading in Zebrafish Epiboly, IST
    Austria, 2014.
corr_author: '1'
date_created: 2018-12-11T11:51:49Z
date_published: 2014-08-01T00:00:00Z
date_updated: 2026-03-09T14:56:18Z
day: '01'
ddc:
- '590'
degree_awarded: PhD
department:
- _id: CaHe
file:
- access_level: closed
  checksum: 67df5501b1b5b313c3bf9a360d713693
  content_type: application/pdf
  creator: cchlebak
  date_created: 2026-03-09T14:53:14Z
  date_updated: 2026-03-09T14:53:14Z
  file_id: '21421'
  file_name: 2014 Behrnd final.pdf
  file_size: 24842978
  relation: main_file
file_date_updated: 2026-03-09T14:53:14Z
has_accepted_license: '1'
language:
- iso: eng
month: '08'
oa_version: None
page: '91'
publication_status: published
publisher: IST Austria
publist_id: '5804'
related_material:
  record:
  - id: '2282'
    relation: part_of_dissertation
    status: public
  - id: '2950'
    relation: part_of_dissertation
    status: public
  - id: '3373'
    relation: part_of_dissertation
    status: public
status: public
supervisor:
- first_name: Carl-Philipp J
  full_name: Heisenberg, Carl-Philipp J
  id: 39427864-F248-11E8-B48F-1D18A9856A87
  last_name: Heisenberg
  orcid: 0000-0002-0912-4566
title: Forces driving epithelial spreading in zebrafish epiboly
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2014'
...