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SUMMARY:Mechanical forces driving zebrafish epiboly - Dr Carl-Philipp Heis
 enberg\, IST Austria\, Klosterneuburg\, Austria
DTSTART:20110920T153000Z
DTEND:20110920T155500Z
UID:TALK31867@talks.cam.ac.uk
CONTACT:Duncan Simpson
DESCRIPTION:The molecular and cellular mechanisms by which tissues take sh
 ape are fundamental to many biological processes. While the genetic pathwa
 ys controlling tissue morphogenesis have been intensively analyzed\, its m
 echanical principles are poorly understood. An excellent assay system to s
 tudy the biophysical basis of tissue morphogenesis is zebrafish gastrulati
 on\, where within a few hours major morphogenetic changes result in the fo
 rmation of germ layers and the establishment of the body axis.\nTo obtain 
 insight into the biophysical basis of tissue morphogenesis during gastrula
 tion\, we study enveloping cell layer (EVL) epiboly\, the spreading of a s
 quamous epithelium over the yolk cell. A circumferential actomyosin band w
 ithin the yolk syncytial layer (YSL) has been proposed to act as a purse s
 tring pulling on the EVLmargin. However\, direct evidence supporting this 
 hypothesis has been missing. Using laser ablation to measure tension withi
 n the actomyosin band\, we find an anisotropic tension distribution with h
 ighest tension parallel to the EVL margin. Notably\, there is also tension
  perpendicular to the EVL margin\, indicating that the actomyosin band is 
 not free to constrict in this direction. To understand how anisotropic ten
 sion within the actomyosin band controls EVL epiboly\, we have developed a
  hydrodynamic description of this process\, modeling the actomyosin cortex
  as an active\, viscoelastic gel. Quantifications of cortical flows within
  the EVL and YSL are consistent with predictions from our theory\, support
 ing the general plausibility of our theoretical approach.\nBased upon expe
 rimental and theoretical results\, we propose a new mechanism for the acto
 myosin band in EVL epiboly: in addition to function as a geometry-dependen
 t purse string\, it exerts a friction-based pulling force. \nMartin Behrnd
 t\, Guillaume Salbreux\, Stephan Grill\, Carl-Philipp Heisenberg\nhttp://w
 ww.ist.ac.at/research/research-groups/heisenberg-group/\n
LOCATION:MR2\, Centre for Mathematical Sciences\, Wilberforce Road\, Cambr
 idge
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