Intracellular microrheology of motile Amoeba proteus

TL;DR

This study used passive particle tracking microrheology to analyze the viscoelastic properties and flow behavior of Amoeba proteus's cytoplasm, revealing differences between cortex and endoplasm and their rheological characteristics.

Contribution

It introduces a novel application of particle tracking microrheology to study intracellular mechanics in Amoeba proteus, highlighting distinct viscoelastic behaviors.

Findings

Cortex exhibits semiflexible actin fiber dynamics with a rheological exponent of 3/4.

Endoplasm shows shear-thinning behavior with increasing flow rate.

Viscoelastic properties differ significantly between cortex and endoplasm.

Abstract

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.