Tag: Poster 51

Tramtrack69 Restricts Axon Growth through the Activin Signaling Pathway

Presenter: Alex Whitebirch

Mentor: Tory Herman

AM Poster Presentation

Poster 51

Connections between nerve cells are established by the outgrowth of long projections called “axons.” The motile end of a growing axon is the growth cone, a dynamic structure of actin filaments and microtubules. We are interested in how neurons downregulate the motility of their growth cones once the latter have reached their final targets. Studying this process may improve our under standing of how neurons control growth cone motility during regeneration after injury. In the Drosophila eye, R7 photoreceptor neurons are born in the retina of the fly and project their axons into the optic lobe. The Herman lab has found that the transcription factor Tramtrack69 (Ttk69) is required to prevent R7 axons from continuing to grow even after they reach their targets. Ttk69 is absent from R7s during axon outgrowth but present in R7s as their axons approach their targets. Early misexpression of Ttk69 causes premature termination of R7 axons. We conclude that Ttk69 is both necessary and sufficient to restrict axonal growth. We have found that Ttk69 does so by promoting signaling through the conserved TGF/Activin pathway. Because Ttk69 is known to be a transcriptional repressor, we hypothesize that Ttk69 represses an antagonist of the Activin pathway. Using RNA interference, I will disrupt expression of genes known to antagonize Activin signaling, including follistatin and cripto-like, in R7 cells lacking Ttk69. Suppression of the ttk69 mutant phenotype would indicate that the gene in question might be a target of Ttk69 repression.

Probing the Nucleic Acid Binding Properties of the Single-stranded DNA Binding Protein of bacteriophage T4 Replication Complex at Single Nucleotide Resolution

Presenter: Benjamin Camel

Co-Presenters: Katherine Meze, Davis Jose, Peter von Hippel

Faculty Mentor: Davis Jose, Peter von Hippel

Presentation Type: Poster 51

Primary Research Area: Science

Major: Biochemistry

Funding Source: GM-15792, NIH, $350k/yr. (4 yrs.)

Previous studies have mapped the structural details and assembly properties of the single-stranded (ss)DNA binding protein (gp32) of bacteriophage T4 as it binds to various ssDNA lattices, both as isolated monomers and as cooperatively bound gp32 clusters. Building on previous studies, our work seeks to understand these binding interactions at single nucleotide resolution. We have utilized site-specifically positioned 2-aminopurine (2-AP) fluorescent base analogs of adenine incorporated into ssDNA lattices as either monomer or dimer-pair probes, to map the detailed interactions of gp32 with ssDNA lattices of various lengths. To this end we have employed changes in the fluorescent and circular dichroism (CD) spectra of these probes in order to determine how the binding site of the protein interacts with these site-specifically positioned probes. Our results demonstrate that gp32 binds at random at low concentrations, and then shifts to preferential binding at the 5’-end of the lattice as the proteins shift into cooperative, cluster-bound forms at higher gp32 concentrations. We have also used acrylamide quenching to monitor solvent exposure of the ssDNA bases at various lattice positions. These results provide new insights into the molecular mechanisms of the gp32-ssDNA interactions that are involved in controlling the functions of the T4 DNA replication complex.

Investigating How Light Regulates Protein Synthesis in Chloroplasts

Presenter(s): Carolyn Brewster – Biology, Math and Computer Science

Faculty Mentor(s): Alice Barkan

Poster 51

Research Area: Natural/Physical Science

Funding: O’Day Fellowship

Photosynthesis provides the fuel for earth’s biomes. The protein PsbA is essential for photosynthesis but is also damaged as a consequence of photosynthesis; PsbA must therefore be constantly replaced to maintain photosynthetic activity. Accordingly, PsbA synthesis increases dramatically within minutes after shifting plants from dark to light. The mechanisms underlying this response are not known. We are investigating these mechanisms with a two-pronged approach: we are studying proteins that we suspect may be involved in PsbA light-regulation, and we are designing protein “tags” to isolate potential regulators that are attached to PsbA mRNA. We identified two candidate regulators, HCF244 and TPJ1, based on their patterns of gene expression. Using a combination of techniques, we discovered that HCF244 is required for PsbA synthesis whereas TPJ1 is not. We found that TPJ1 activates production of a different protein involved in photosynthesis. Thus, HCF244 is a good candidate for regulating PsbA synthesis in response to light, but TPJ1 is not. In the second approach, we designed a method to engineer proteins to bind specifically to the PsbA RNA. We expressed these engineered proteins in plants and confirmed that they bind specifically to PsbA RNA in vivo. We are using these proteins as “hooks” to purify PsbA RNA and the proteins bound to it. These will be evaluated for their role in PsbA regulation. In addition to elucidating mechanisms that regulate production of the photosynthetic apparatus, this is the first demonstration that proteins can be designed to purify specific RNA-protein particles from an organism.

Modulating Diradical Character in Indenoindenodibenzothiopene and Benzofluorenofluorene Structures For Ultimate Application Within Organic Electronics

Presenter(s): Eric Strand

Faculty Mentor(s): Michael Haley & Joshua Barker

Poster 51

Session: Sciences

The Haley Lab is interested in the synthesis and characterization of organic hydrocarbon scaffolds which can be used as semiconductors. The family of indenofluorene hydrocarbons exhibit unique electronic properties such as antiaromaticity and diradical character, which contribute to their allure for scientists. Our lab has developed highly modular synthetic routes toward many analogues of this parent scaffold, which can be further optimized through subtle synthetic tuning. Our ultimate goal is to create a library of analogues with tuned electronic characteristics such that we may identify the most promising candidates for device implementation. Fusing a variety of aryl moieties onto the parent scaffold allows for this by decreasing the HOMO-LUMO energy gap and subsequently improvement in electron mobility and conductivity. Initially focused on proving the diradical character in an analogue of indenoindenodibenzothiopene, our current project has successfully shown this by reacting the molecule through a known radical degradation pathway.

Our studies into indenofluorenes have shown promise in regard to the ability of these molecules to serve as potential replacements for current inorganic counterparts within devices. Continuous fundamental studies into the electronic abilities of these molecules will help to elucidate the ideal characteristics of organic semiconductors, which is imperative for the feasible implementation of these molecules into devices. This project is now focused on the optimization of previous synthetic routes such that further studies into these highly interesting molecules can be carried out.