CSB2: Council for Systems Biology in Boston
CCC2009 poster prize winners announced
Published January 27, 2009
Over 30 posters were presented at Cells, Circuits, and Computation on January 23, 2009. CSB2 is happy to announce that Luke Thompson (MIT Biology) and Yoram Burak (Harvard Center for Brain Science) won the two poster prizes. The abstracts of their poster presentations follow:
Viruses hijacking cyanobacterial carbon metabolism
Luke R. Thompson1, JoAnne Stubbe1,2, and Sallie W. Chisholm1,3
Departments of 1: Biology, 2: Chemistry, and 3: Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge MA
Cyanophage infecting the marine cyanobacteria Prochlorococcus and Synechococcus carry several genes involved in the pentose phosphate pathway (PPP), a nighttime alternative to the Calvin cycle that generates NADPH and ribose. Oxidizing conditions in cyanobacteria at night, when photosystem I cannot generate NADPH, favor flux through the PPP, including the key enzyme transaldolase. Many cyanophage carry a transaldolase gene (talC) that differs markedly in structure from the host transaldolase (talA), suggesting that its acquisition and maintenance by cyanophage stems from functional differences with the host transaldolase. We have shown that the host enzyme is subject to oxidation in aerobic conditions, requiring reductant for full activity, whereas the phage transaldolase has no such effect. Site-directed mutagenesis of host transaldolase cysteines suggests that a mechanism independent of disulfide bond formation is responsible for this redox effect. We have recently found that another PPP-related gene, for the photosynthetic regulatory protein CP12, is also carried by many cyanophage. In cyanobacteria and other phototrophs, CP12 binds and deactivates two Calvin cycle enzymes under nighttime oxidizing conditions, promoting flux through the PPP. It therefore seems that cyanophage promote flux through the PPP by encoding not only enzymes but also a regulatory protein that inhibits the competing Calvin cycle. Phage infection of some cyanobacteria is known to lead to oxidizing conditions. Oxidative inactivation of host transaldolase and activation of phage CP12 may therefore be physiologically important, allowing cyanophage to produce NADPH and ribose for nucleotide biosynthesis and genome replication. Abundance patterns in phage genomes of talC, cp12, and two phage-encoded PPP dehydrogenases (zwf and gnd) are mirrored in environmental sequence databases, suggesting that the metabolic hijacking of cyanobacteria by cyanophage may be a globally important phenomenon.
Fly Magnetism: Planar Cell Polarity in Drosophila Development
Yoram Burak1,2 and Boris Shraiman2
1: Center for Brain Science, Harvard University, Cambridge, MA
2: Kavli Institute for Theoretical Physics, UCSB, Santa Barbara, CA
Cells in the wing blade of Drosophila Melanogaster exhibit an in-plane polarization causing distal orientation of hairs. Establishment of the Planar Cell Polarity (PCP) involves intercellular interactions as well as a global orienting signal. Many of the genetic and molecular components underlying this process have been experimentally identified and a recently advanced system-level model by Amonlirdviman et al (2005) has demonstrated that many of the observed mutant phenotypes can be understood in terms of intercellular interactions involving asymmetric localization of membrane bound proteins. Among key open questions in understanding the emergence of ordered polarization is the effect of stochasticity and the role of the global orienting signal. These issues relate closely to our understanding of ferromagnetism in physical systems. Here we pursue this analogy to help understand how PCP order and its response to perturbations depend on the parameters of a semi-phenomenological model of the underlying molecular processes. We define a “phase diagram” of the model which provides a global view of the dependence of the phenotype on the parameters. We show that the dynamics of PCP has two regimes: rapid growth in the amplitude of local polarization followed by a slower process of alignment which progresses from small to large scales. We discuss the response of the tissue to various types of orienting signals and show that global PCP order can be achieved with a weak orienting signal provided that it acts during the early phase of the process. Finally we define and discuss some of the experimental predictions of the model.