@article {70083, title = {An expanded palette of bright and photostable organellar Ca2+ sensors}, journal = {eLife}, year = {2025}, month = {2025 Aug 26}, abstract = {

The use of fluorescent sensors for functional imaging has revolutionized the study of organellar Ca2+\ signaling. However, understanding the dynamic interplay between intracellular Ca2+\ sinks and sources has been hindered by the lack of bright, photostable, and multiplexed measurements in different organelles, limiting our ability to define how Ca2+\ shapes cell physiology across fields of biology. Here we introduce a new toolkit of chemigenetic organellar Ca2+\ indicators whose color is tunable by reconstituting their fluorescence with different exogenous rhodamine dye-ligands, which significantly expand the capacity for multiplexing organellar Ca2+\ measurements. These sensors, which we named ER-HaloCaMP and Mito-HaloCaMP, are optimized to report Ca2+dynamics in the endoplasmic reticulum (ER) and mitochondria of mammalian cells and neurons, and show significantly improved brightness, photostability and responsiveness when compared to current best-in-class alternatives. Using either red or far-red dye-ligands, both ER-HaloCaMP and Mito-HaloCaMP enable visualizing ER and mitochondrial Ca2+\ dynamics in neuronal axons, a subcellular location that only contains a few ER tubules and small mitochondria, structural limitations that have impaired measurements with previous red sensors. To show the expanded multiplexing capacities of our toolkit, we measured interorganellar Ca2+\ fluxes simultaneously in three different subcellular compartments in live cells, revealing that the amplitude of ER Ca2+release controls the efficacy of ER-mitochondria Ca2+\ coupling in a cooperative manner. Organellar HaloCaMPs enable also measuring Ca2+\ dynamics in intact brain tissue from flies and rodents, demonstrating their versatility across biological models. Our new toolkit provides an expanded palette of bright, photostable and responsive organellar Ca2+\ sensors, which will facilitate future studies of intracellular Ca2+\ signaling across fields of biology in health and disease.

}, doi = {10.7554/elife.107845.1}, url = {http://dx.doi.org/10.7554/eLife.107845.1}, author = {Moret, Agathe and Farrants, Helen and Fan, Ruolin and Zingg, Kelsey G and Silva, Bryon and Roselli, Camilla and Oertner, Thomas G and Gee, Christine E and Hadjieconomou, Dafni and Rangaraju, Vidhya and Schreiter, Eric R and de Juan-Sanz, Jaime} } @article {68915, title = {Rational Engineering of an Improved Genetically Encoded pH Sensor Based on Superecliptic pHluorin.}, journal = {ACS Sensors}, volume = {8}, year = {2023}, month = {2023 Aug 25}, pages = {3014-3022}, abstract = {

Genetically encoded pH sensors based on fluorescent proteins are valuable tools for the imaging of cellular events that are associated with pH changes, such as exocytosis and endocytosis. Superecliptic pHluorin (SEP) is a pH-sensitive green fluorescent protein (GFP) variant widely used for such applications. Here, we report the rational design, development, structure, and applications of Lime, an improved SEP variant with higher fluorescence brightness and greater pH sensitivity. The X-ray crystal structure of Lime supports the mechanistic rationale that guided the introduction of beneficial mutations. Lime provides substantial improvements relative to SEP for imaging of endocytosis and exocytosis. Furthermore, Lime and its variants are advantageous for a broader range of applications including the detection of synaptic release and neuronal voltage changes.

}, issn = {2379-3694}, doi = {10.1021/acssensors.3c00484}, author = {Shen, Yi and Wen, Yurong and Sposini, Silvia and Vishwanath, Anjali Amrapali and Abdelfattah, Ahmed S and Schreiter, Eric R and Lemieux, M Joanne and de Juan-Sanz, Jaime and Perrais, David and Campbell, Robert E} } @article {48266, title = {Axonal Endoplasmic Reticulum Ca(2+) Content Controls Release Probability in CNS Nerve Terminals.}, journal = {Neuron}, volume = {93}, year = {2017}, month = {2017 Jan 30}, pages = {867-81}, abstract = {

Although the endoplasmic reticulum (ER) extends throughout axons and axonal ER dysfunction is implicated in numerous neurological diseases, its role at nerve terminals is poorly understood. We developed novel genetically encoded ER-targeted low-affinity Ca(2+) indicators optimized for examining axonal ER Ca(2+). Our experiments revealed that presynaptic function is tightly controlled by ER Ca(2+) content. We found that neuronal activity drives net Ca(2+) uptake into presynaptic ER although this activity does not contribute significantly to shaping cytosolic Ca(2+) except during prolonged repetitive firing. In contrast, we found that axonal ER acts as an actuator of plasma membrane (PM) function: [Ca(2+)]ER controls STIM1 activation in presynaptic terminals, which results in the local modulation of presynaptic function, impacting activity-driven Ca(2+) entry and release probability. These experiments reveal a critical role of presynaptic ER in the control of neurotransmitter release and will help frame future investigations into the molecular basis of ER-driven neuronal disease states.

}, issn = {1097-4199}, doi = {10.1016/j.neuron.2017.01.010}, author = {de Juan-Sanz, Jaime and Holt, Graham T and Schreiter, Eric R and de Juan, Fernando and Kim, Douglas S and Ryan, Timothy A} }