The cartography of cell motion
Tyson, R. A. (Richard Anthony) (2011) The cartography of cell motion. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2581468~S1
Cell motility plays an important role throughout biology, the polymerisation of actin
being fundamental in producing protrusive force. However, it is increasingly apparent
that intracellular pressure, arising from myosin-II contraction, is a co-driver of motility.
In its extreme form, pressure manifests itself as hemispherical protrusions, referred to as
blebs, where membrane is torn from the underlying cortex. Although many components
and signalling pathways have been identified, we lack a complete model of motility,
particularly of the regulation and mechanics of blebbing. Advances in microscopy are
continually improving the quality of time series image data, but the absence of highthroughput
tools for extracting quantitative numbers remains an analysis bottle-neck.
We develop the next generation of the successful QuimP software designed for
automated analysis of motile cells, producing quantitative spatio-temporal maps of protein
distributions and changes in cell morphology. Key to QuimP's new functionality,
we present the Electrostatic Contour Migration Method (ECMM) that provides high
resolution tracking of local deformation with better uniformity and efficiency than rival
methods. Photobleaching experiments are used to give insight into the accuracy and
limitations of in silico membrane tracking algorithms. We employ ECMM to build an
automated protrusion tracking method (ECMM-APT) sensitive not only to pseudopodia,
but also the complex characteristics of high speed blebs.
QuimP is applied to characterising the protrusive behaviour of Dictyostelium,
induced to bleb by imaging under agar. We show blebs are characterised by distinct
speed-displacement distributions, can reach speeds of 4.9μm/sec, and preferentially
form at the
anks during chemotaxis. Significantly, blebs emerge from
at to concave
membrane regions suggesting curvature is a major determinant of bleb location, size,
and speed. We hypothesise that actin driven pseudopodia at the leading edge induce
changes in curvature and therefore membrane tension, positive curvature inhibiting
blebbing at the very front, and negative curvature enhancing blebbing at the sides.
This possibly provides the necessary space for rear advancement. Furthermore, bleb
kymographs reveal a retrograde shift of the cortex at the point of bleb expansion, suggesting
inward contractive forces acting on the cortex even at concave regions. Strains
defficient in phospholipid signalling show impaired chemotaxis and blebbing.
Finally, we present further applications of QuimP, for example, we conclusively
show that dishevelled is not polarised during Xenopus gastrulation, contrary to hypotheses
in the literature.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QH Natural history > QH301 Biology|
|Library of Congress Subject Headings (LCSH):||Cells -- Motility -- Computer programs|
|Official Date:||December 2011|
|Institution:||University of Warwick|
|Theses Department:||Systems Biology Doctoral Training Centre|
|Extent:||xvii, 174 leaves : ill., charts|
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