Calcineurin is a protein phosphatase that is active only in the presence of high concentrations of calcium ions.  It is expressed in many different tissues, and is involved in many activities during development.  In the immune system, calcineurin is turned on during T cell activation in the immune response and dephosphorylates a transcription factor called NFAT, for nuclear factor of activated T cells.  NFAT then turns on the transcription of other proteins in combination with the heteromeric transcription factor AP-1.
    NFAT expression, however, is not restricted to the immune system; several isoforms are also found in the nervous system where it presumably acts as a transcription factor in response to calcium signals mediated by calcineurin.  Calcium entry can be activated during synaptic signaling through the NMDA receptor, and is specifically linked to learning and memory.  Calcium signaling also plays a significant role during neural development and formation of proper connections between neurons.
    Our main question is: what is the role of NFAT in the nervous system?  We are studying NFAT activation in the visual system of Xenopus tadpoles using a fusion protein of NFAT with GFP (green fluorescent protein).  A DNA plasmid which expressed NFAT-GFP is electroporated into tadpoles, visualized with a confocal microscope, and the tadpoles treated with drugs that alter calcium signaling.  The next day the same tadpoles will be imaged again to see how the NFAT-GFP expression changed.  In addition, we will image electroporated tadpoles and then stimulate the visual system with either electrodes or strobe lighting, followed by further imaging.  Lastly, using a calcium sensitive version of GFP called GCaMP, we will study the intracellular calcium levels during various types of drug treatment and visual stimulation.


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