Troponin C-based biosensors: A new family of genetically encoded indicators for in vivo calcium imaging in the nervous system

Fluorescence imaging represents a powerful approach for the detection of intracellular Ca²⁺ signals in vivo. With appropriate techniques, Ca²⁺ signals can be recorded at many levels of complexity, ranging from large scale neuronal networks down to individual presynaptic boutons or postsynaptic spines. Here we review the applicability of genetically encoded Ca²⁺ indicators for in vivo Ca²⁺ imaging of neural function. We describe some of the recent progress in sensor design and evaluate the performance of the new family of Troponin C-based Ca²⁺ indicators. Further, we analyze properties of Ca²⁺ biosensors transgenically expressed in various experimental animal models and illustrate their use for measuring somatic and dendritic Ca²⁺ signals in neurons of the mammalian brain.