Intracellular microrheology of motile Amoeba proteus
Salman S Rogers 1, Thomas A Waigh 1* and Jian R Lu 1
1 University of Manchester
* To whom correspondence should be addressed. E-mail: thomas.waigh{at}manchester.ac.uk.
Submitted on October 12, 2007
Revised on November 5, 2007
Accepted on 16 November 2007
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Abstract |
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The motility of motile Amoeba proteus was examined using the technique of passive particle tracking microrheology, with the aid of newly-developed particle tracking software, a fast digital camera and an optical microscope. We tracked large numbers of endogeneous particles in the amoebae, which displayed subdiffusive motion at short time scales, corresponding to thermal motion in a viscoelastic medium, and superdiffusive motion at long time scales due to the convection of the cytoplasm. Subdiffusive motion was characterised by a rheological scaling exponent of 3/4 in the cortex, indicative of the semiflexible dynamics of the actin fibres. We observed shear-thinning in the flowing endoplasm, where exponents increased with increasing flow rate; i.e. the endoplasm became more fluid-like. The rheology of the cortex is found to be isotropic, reflecting an isotropic actin gel. A clear difference was seen between cortical and endoplasmic layers in terms of both viscoelasticity and flow velocity, where the profile of the latter is close to a Poiseuille flow for a Newtonian fluid.
Key Words:
Amoeba proteus, cytoskeleton, microrheology, motility, particle tracking, viscoelasticity
