Calcium signaling is one of the most universal and versatile intracellular messengers. The versatility of calcium signaling is reflected in its ability to control multiple processes such as autophagy, apoptosis, transcription, development, proliferation, differentiation, metabolism, contraction, secretion, learning, and memory. Various organelles (e.g., eBER, SR, mitochondria), cell types (e.g., nerve cells, muscle cells, pancreatic cells, stem cells, cancer cells), tissues (e.g., neural tissue, sensory tissue, endocrine tissue), organs (e.g . , heart, brain, muscle) and animal models (e.g., mice, zebrafish, Drosophila, C. elegans) exhibit unique features of Ca2+ dynamics to mediate desired physiological processes.

Monitoring the Ca2+ dynamics provides mass information for the mechanistic studies of physiological and pathological processes. The genetically encoded calcium indicators (GECIs), such as the GCaMP series, GCaMP-X, XCaMP series, CaMPARI, and RCaMP, have been the most popular tools for calcium measurement, which allow us to monitor calcium dynamics from the superresolution level to the whole organ or animal level. Beyond that, chemical Ca2+ dyes (e.g., fura-2, OGB, fluo-4) also provide a simple but not long-lasting solution for calcium monitoring. This Methods Collection will concentrate on strategies for selecting and employing appropriate calcium indicators to monitor Ca2+ dynamics in living organisms. Detailed information on the selection of GECIs or Ca2+ dyes, targeted living organisms, protocols of indicator loading or expression, equipment for Ca2+ imaging, and settings for Ca2+ imaging will be provided in this collection.