Ca2+ signalling and early embryonic patterning during zebrafish development

It has been proposed that Ca2+ signalling, in the form of pulses, waves and steady gradients, may play a crucial role in key pattern-forming events during early vertebrate development. With reference to the embryo of the zebrafish (Danio rerio), herein we review the Ca2+ transients reported from the cleavage to segmentation periods. This time-window includes most of the major pattern-forming events of early development, which transform a single-cell zygote into a complex multicellular embryo with established primary germ layers and body axes. Data are presented to support our proposal that intracellular Ca2+ waves are an essential feature of embryonic cytokinesis and that propagating intercellular Ca2+ waves (both long and short range) may play a crucial role in: (i) the establishment of the embryonic periderm and the coordination of cell movements during epiboly, convergence and extension; (ii) the establishment of the basic embryonic axes and germ layers; and (iii) definition of the morphological boundaries of specific tissue domains and embryonic structures, including future organ anlagen. The potential downstream targets of these Ca2+ transients are also discussed, as well as how they may integrate with other pattern-forming signalling pathways known to modulate early developmental events.