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giving a giant talk

Aurelia R. Honerkamp-Smith

Postdoctoral researcher

fellow of Churchill College

Current work

I'm currently a postdoctoral researcher in the Goldstein lab. I'm an experimentalist. I study the interactions between fluid flow, lipid membranes and membrane proteins. I'm also interested in the physics of development in green algae.






Tigra Fader Sample #1 - Simple Slide Show Some recent experimental images. For details see below or the publications page.



PRL cover image

Vesicles

I'm interested in using fluid flow to move and sort membrane lipids and proteins. In a recently published paper, I used confocal movies like the ones below to reconstruct the 3D flow field throughout vesicles. Using a calculation by Francis G. Woodhouse, the flow field can be used to measure the membrane viscosity.










Movies of polystyrene beads (green) flowing inside and outside a hemispherical vesicle (red) at three different heights in the vesicle.


Volvox inversion

Volvox carteri is a microscopic swimming algae which forms a hollow sphere. The spheroid consists of somatic cells, each of which has a photoreceptor and two flagella. Inside are the germ cells which will become the next generation. The spheroid coordinates the beating of its flagella to steer towards light. Each spheroid arises from a germ cell that initially develops inside out, with the flagella pointing towards the center. The developing embryo therefore inverts as soon as cell division has finished.

Recently I have been using a light sheet microscope to record live movies of inversion in V. carteri: click on the lefthand picture to watch. Or, if you have red and blue anaglyph glasses, click on the righthand picture to watch in 3D!

carteri_motherbw carteri_mother3D

With Stephanie Höhn I have been working on recording movies of inversion in V. globator embryos, and comparing their shapes with a model devised by Pierre Haas. This movie shows the results.

top of a chara plant

Chara

Another model organism used in the Goldstein lab is Chara australis, also known as stonewort. It is a freshwater algae with large cells in which cytoplasmic streaming is easily visible, and streaming in Chara has been studied for many years. Each individual cell of the plant, seen in the image at left, is about 1 mm wide, and can be many centimeters long.









Previous work

I did my PhD research with Prof. Sarah L. Keller in the Department of Chemistry at the University of Washington, on critical phase transitions in giant unilamellar vesicles.


vesicle images next to ising model images

Static critical exponents

Giant unilamellar vesicles with a ternary composition can separate into coexisting liquid phases. I used fluorescence microscopy and image analysis to show that the fluctuations that appear in ternary lipid bilayers are consistent with the universality class of the 2D Ising model. This work was done in collaboration with Marcel den Nijs (UW Physics), Michael Schick (UW Physics), Marcus Collins (UW Chemistry, currently Biochemistry), Pietro Cicuta (University of Cambridge Physics) and Sarah Veatch (formerly at Cornell, currently at University of Michigan). The paper is here. Similar results are found in plasma membrane vesicles isolated directly from living cells (experiments done by Sarah Veatch, here).



Below, you can watch a temperature quench (a sudden drop of about 4 degrees C) in two different vesicles with an off-critical compositions:

off-critical1 off-critical1

The temperature quench looks different when the vesicle has a composition close to the critical point (this movie and the two above were recorded as described in this paper):

spinodal

At constant temperature, persistent fluctuations are observed, both above and below the critical temperature. These movies show the vesicle from figure 1 of this paper.

critical fluct 6 critical fluct 5 critical fluct 4 critical fluct 3 critical fluct 2 critical fluct 1


dynamic scaling collapse

Dynamic critical exponent

More recently, I used similar techniques to find the dynamic critical exponent for bilayer concentration fluctuations. Once dynamics are considered, the 2-D Ising universality class breaks into multiple sub-classes that depend on the mechanism by which lipid momentum is dissipated. Critical dynamics in lipid membranes are governed not only by membrane properties, but also by how the membrane couples to the surrounding bulk fluid. Ben Machta at Cornell (now at Princeton) was instrumental in interpreting and analyzing this experiment, which is now published.