Investigating a Signaling Mechanism for the Establishment of Cellular Polarity Through the Detection of Protein Interactions with the FdRacA Small GTPase
Presented by: Derek Rains
Mentor: John Fowler
Department of Botany/Plant Pathology, Oregon State University

During early embryonic development, zygotes of the brown alga Fucus distichus begin to develop a "bud" which orients itself in a direction away from a nearby unilateral light source. This development of polarity in the cells provides both a direction for zygotic growth as well as an orientation for the first plane of cell division. Localized in the growing tip of the polarizing zygotes is the Fucus protein FdRacA, which is a small GTPase. FdRacA is likely to be a signaling molecule that aids in the establishment of cellular polarity. Therefore of particular interest to the understanding of the biological pathway by which cell polarity is defined is the identification of other proteins which specifically interact with FdRacA. Candidate interacting proteins could either act upstream of FdRacA by assisting the conversion of the protein to its active GTP bound form, or may interact downstream of the active FdRacA in a signaling cascade which leads to polar growth. To investigate these possibilities, I used a yeast two hybrid screen to isolate over 120 candidate interactors. The yeast two hybrid screen works on the premise that only FdRacA interacting proteins from a Fucus cDNA library will be selected for by growth of transformed yeast colonies on a selective medium. Three interesting candidates I have identified so far show simflarities to myosin, the trans-membrane protein Notch, and an aldolase. Possible hypotheses for the function of these candidates in a signaling cascade mechanism will be presented.