Engineering Approaches to Biomolecular Motors

Engineering Approaches to Biomolecular Motors: From in vitro to in vivo Friday Speaker Abstracts

Optical Coherence Tomography for Depth-resolved Imaging of Intracellular Motility in

Mammary Epithelial Cell Organoids and Excised Tissue

Amy Oldenburg

1,2,3

, Xiao Yu

, Liza Makowski

, Melissa Troester

University of North Carolina at Chapel Hill, Department of Physics & Astronomy, Chapel Hill,

NC, USA,

University of North Carolina at Chapel Hill, Department of Biomedical Engineering,

Chapel Hill, NC, USA,

Lineberger Comprehensive Cancer Center, University of North

Carolina at Chapel Hill, Chapel Hill, NC, USA.

Optical Coherence Tomography (OCT) is a method for real-time, depth resolved imaging with

micrometer-scale resolution. OCT employs low-coherence interferometry which enables imaging

several mean-free scattering path lengths into tissues and 3D cell cultures (typically >1 mm).

Here we use OCT to study the intracellular motility of mammary epithelial cell (MEC) organoids

grown in 3D tissue culture, as well as freshly excised mouse mammary tissue. This motility is

apparent as a speckle fluctuation in OCT corresponding to nanoscale motions of light scattering

cellular features. The power spectrum of the observed speckle fluctuations exhibits 1/f power law

scaling over the range from 0.01 – 1 Hz, and is notably inconsistent with the Lorentzian profile

expected for Brownian motion.

We studied changes in the apparent motility of an MEC line (

in 3D culture

longitudinally (1hr – 6 days) after exposure to a variety of substances: doxorubicin and taxol

(chemotherapeutics), estrogen (a hormone), and blebbistatin (a myosin II inhibitor). Significant

changes in the motility spectra compared to control were found (p<0.01). Furthermore, freshly

excised mouse mammary tissue displayed significantly different motility spectra from formalin-

fixed (p<0.001).

OCT provides a new capability for visualizing the amplitude and fluctuation spectrum of

intracellular motility over the entire cross-section of an organoid or tissue. Future experiments

aim for a better understanding of subcellular components, including molecular motors, giving

rise to the observed non-Brownian speckle fluctuations. This represents a novel tool for

understanding changes in nonequilibrium cell motion in organized tissues.