Aequorin-based genetic approaches to visualize Ca ²⁺ signaling in developing animal systems

Background: In recent years, as our understanding of the various roles played by Ca ^{2 +} signaling in development and differentiation has expanded, the challenge of imaging Ca ^{2 +} dynamics within living cells, tissues, and whole animal systems has been extended to include specific signaling activity in organelles and non-membrane bound sub-cellular domains. Scope of review: In this review we outline how recent advances in genetics and molecular biology have contributed to improving and developing current bioluminescence-based Ca ^{2 +} imaging techniques. Reporters can now be targeted to specific cell types, or indeed organelles or domains within a particular cell. Major conclusions: These advances have contributed to our current understanding of the specificity and heterogeneity of developmental Ca ^{2 +} signaling. The improvement in the spatial resolution that results from specifically targeting a Ca ^{2 +} reporter has helped to reveal how a ubiquitous signaling messenger like Ca ^{2 +} can regulate coincidental but different signaling events within an individual cell; a Ca ^{2 +} signaling paradox that until now has been hard to explain. General significance: Techniques used to target specific reporters via genetic means will have applications beyond those of the Ca ^{2 +} signaling field, and these will, therefore, make a significant contribution in extending our understanding of the signaling networks that regulate animal development. This article is part of a Special Issue entitled Biochemical, biophysical and genetic approaches to intracellular calcium signalling.