Beckman Institute Graduate Student Seminar Scheduled for September 26

The Fall 2007 Beckman Institute Graduate Student Seminar Series begins Wednesday, September 26. Three short presentations will be featured: "A Mechanistic Approach to the Identification and Interpretation of Contrast in Viscoelasticity Imaging" by Rebecca Yapp; and "Genotype x Environment: Caste Determination in an Ant Society" by Christopher Smith; and "Macromolecular Yoga: Merging Data from Different Resolutions to Reveal Biomolecular Function" by Elizabeth Villa. The hour-long seminar begins at Noon and is open to the public. It will be held in Beckman Institute Room 1005 and lunch will be served.

The Beckman Institute Graduate Student Seminar Series presents the work of outstanding graduate students working in Beckman research groups. The seminars begin at Noon in Beckman Institute Room 1005 and are open to the public. Lunch will be served.

A Mechanistic Approach to the Identification and Interpretation of Contrast in Viscoelasticity Imaging
Rebecca Yapp

Ultrasonic elasticity imaging is emerging as a useful tool for breast cancer detection. It is a technique by which a stress is applied to tissue and the strain is mapped as a function of position. Contrast in strain images is provided by differences in the mechanical properties of tissue. Breast tissue can be considered a viscoelastic polymer system. To consider both the elastic and viscous properties we turn to a technique we call viscoelasticity imaging which maps the strain as a function of both position and time. It has been shown that additional imaging parameters can be obtained from the time varying strain data. In my studies, I experimentally model breast tissue with a gelatin phantom which allows the flexibility to change the properties to mimic breast cancer conditions. My research project focuses on understanding the mechanisms by which contrast occurs to aid in both finding and understanding image contrast for these disease specific conditions. Mechanical testing studies in the form of creep and stress relaxation are used to analyze the effect of various conditions on a macroscopic scale and compression tests monitored by Fourier Transform-Infrared Spectroscopy are used to gain a molecular level understanding.

Genotype x Environment: Caste Determination in an Ant Society
Christopher Smith

Caste is a hallmark of social evolution. Research has shown that caste can be determined exclusively by either nutritional variation among individuals or by genetic differences. Both environmental and genetic caste determination systems affect the nature of colony demographic regulation and fitness. In most cases, however, caste is likely an interaction between both genotype and environment. In this study we investigated both the nutritional and genetic influence on caste in the Florida harvester ant, Pogonomyrmex badius, which produces three distinct female morphs: minor workers, major workers and reproductive females. Our methods included experimentally manipulating colony food supplies, stable isotope analyses, and genotyping of individuals. Overall, this research demonstrates that caste is a complex interaction of nutritional and genetic factors. The caste determination system of Pogonomyrmex badius is intermediate between the extremes of completely genetic and environmental (phenotypic plasticity) caste determination, allowing flexibility in allocation decisions, but insuring that all castes can be produced even in the absence of environmental influences.

Macromolecular Yoga: Merging Data from Different Resolutions to Reveal Biomolecular Function
Elizabeth Villa

A key to understanding how biological systems function is to look at their structures captured at work. Experimental techniques reveal different levels of macromolecular structure: high-resolution techniques such as X-ray crystallography contain atomistic details, but the structures obtained are often in non-functional states; alternatively, techniques such as cryo-electron microscopy capture the system in a biologically functional state, albeit at low resolution. Computational techniques can bridge the resolution gap by adapting crystallographic structures to electron microscope density maps, thus providing the details of the molecules in different functional states; and by analyzing their physical and dynamical properties, thus revealing astonishing views of cellular processes. This lecture will present a novel method for combining multiresolution data to obtain atomistic structures of macromolecules in functional states. Examples of applications will include structures of poliovirus at different stages of infection, the complete structure of the flagellar hook of bacteria, and the structure of a bacterial ribosome upon antibiotic binding, which results in the death of the bacteria.