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Comment les amibes utilisent-elles la physique
pour survivre?
Marcus Hauser Abteilung Biophysik,
Otto-von-Guericke-Universität Magdeburg
Ecole interdisciplinaire d'échanges et de
formation en biologie Île de Berder, 29 Mars 4
Avril 2009
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Otto von Guericke
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Dictyostelium discoideum
Life cycle
unicellular
multicellular
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Waves and cell aggregation

• starvation
• solution
• cell aggregation
• cellcell communication

cAMP - signal transduction - chemoattractant ?
chemotaxis
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Dictyostelium discoideum

• Martiel Goldbeter
• extracellular
  intracellular

inhibition of cAMP degradation activation of gene
expression
neighbouring cells
receptor active inactive
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Dictyostelium discoideum

• Production / release of cAMP
• autocatalytic process
• Membrane receptors have refractory
• phase

• considered
• reaction
• diffusion (of cAMP)
• missing
• - cell density

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Dictyostelium discoideum

• Excitable system
• n cell density
• ? chemotactic mobility
• u activator, cAMP
• v inhibitor, membrane receptor

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Dyctiostelium discoideum
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dark field microskopy - cAMP
bright chemotaxis dark refractory gray ran
dom motion
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dark field microscopy light microscopy cAMP
waves cell motion
15, 5 mm 0,93 mm
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Excitable systems - Characteristics

• Excitability
• 3 phases - excitable
• - excited
• - refractory

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Excitable systems - Characteristics

• Spiral waves

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Excitable systems - Characteristics
collision of wave fronts ? annihilation of
waves ? formation of territories
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formation of territories
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formation of territories
simulation Voronoi tesselation experiments dev
iation from Voronoi tesselation due to
stochastic effects
AA Polezhaev, C. Hilgardt, T. Mair, SC Müller,
IEE Proc. Syst. Biol. 2005, 152, 75 - 79
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cell streams
x
t
P. Vanková, J. Cejková, C. Hilgardt, L.
Šebestíková, MJB Hauser, H. Ševcíková, CHISA
Porceedings, Academia, Prag, 2005
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aggregation without cell streams
Additon of 3',4'-O-isopropylidenadenosine
IPA cAMP
outside inside
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aggregation without cell streams
0.25 mM IPA IPA IPA
C. Hilgardt, J. Cejková, MJB Hauser, H.
Ševcíková, Biophys Chem 2008, 132, 9 - 17
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aggregation without cell streams
with cell streams
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aggregation without cell streams

• in presence of IPA
• long range waves
• no cell streams
• but formation of small
• territories
• normal friuting bodies
• high number of spores
• IPA acts as inhibitor of
• ACA
• Dynamics as reporter of
• changes in functionality

density of spores
X
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other stages
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Slug, Pseudoplasmodium
C. Weijer, Dundee
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Slug, Pseudoplasmodium
front pre-stalk cells (20 ) rotating
waves back pre-spore cells (80 ) pulsating
waves
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excitability epsp lt epst
scroll wave
model system (Belousov-Zhabotinsky reaction)
z
O2
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Summary
Comment les D. discoydeum untilisent-elles la
pyhsique ?

• aggregation phase excitable systems
• reaction diffusion
• chemotaxis
• excitiation waves (spirals) organising centres
• (pace makers)
• territory formation
• Pseudoplasmodium scroll waves
• internal organisation
• genetic "checkpoints" link to gene / protein
• expression

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