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METHODS IN CELL PHYSIOLOGY
1Department of Medicine and 2Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, Chicago, Illinois 60637
Submitted 19 March 2004 ; accepted in final form 21 May 2004
The use of biosynthetic fluorescent sensors is an important new approach for imaging Ca2+ in cells. Genetically encoded indicators based on green fluorescent protein, calmodulin, and fluorescence resonance energy transfer (FRET) have been utilized to measure Ca2+ in nonmammalian transgenic organisms and provide information about the organization and regulation of Ca2+ signaling events in vivo. However, expression of biosynthetic FRET-based Ca2+ indicators in transgenic mammals has proven to be problematic. Here, we report transgenic expression of an endoplasmic reticulum (ER) Ca2+ biosensor in mouse pancreas. We targeted expression of a yellow cameleon3.3er (YC3.3er) transgene with mouse insulin I promoter. YC3.3er protein expression was limited to pancreatic
-cells within islets of Langerhans and absent in the exocrine pancreas and other tissues. Animals developed and matured normally; sensor expression was unaffected by age. Glucose tolerance in transgenic mice was also unaffected, indicating the transgenic biosensor did not impair endocrine pancreas function. ER Ca2+ responses after administration of thapsigargin, carbachol, and glucose were measured in individual
-cells of intact islets using confocal microscopy and confirmed the function of the biosensor. We conclude that controlling transgene transcription with a cell-specific promoter permits transgenic expression of FRET-based Ca2+ sensors in mammals and that this approach will facilitate real-time optical imaging of signal transduction events in living tissues.
intracellular calcium; cameleon; fluorescence resonance energy transfer
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