Intracellular calcium signaling plays important roles to regulate cell activity during embryogenesis and in adult organisms. In this study, we generate stable transgenic lines, Tg[βactin2:GCaMP6s] stl351to leverage the ultra-sensitive calcium indicator GCaMP6s together with the transparent characteristics of zebrafish embryos, for improved in vivo calcium imaging during early embryogenesis. During the cleavage stages, calcium signaling is associated with the cleavage furrow progression in zebrafish. We recently discovered that embryos lacking maternal and zygotic function of atypical cadherin dachsous1b (MZdchs1b) display abnormal cleavages (Li-Villarreal et al., Development, 2015). Using the Tg[bactin:GCaMP6s], we observed that MZdchs1b embryos displayed various furrow positioning, propagation, and deepening defects at cleavage stages.
During the blastula stages, we detected higher frequency of calcium transients in the enveloping layer (EVL) cells, and a longer dorsal-biased calcium signaling window (3-5hpf) in the WT blastomeres compared with earlier studies. We further report the direct visualization of calcium signaling in the gastrula dorsal forerunner cells (DFCs), which are formed by ingression of dorsal surface epithelium cells at the margin in a Nodal signaling dependent manner. Interestingly, we found that excess Nodal signaling not only leads to the increased number of calcium transients, but also an increase of calcium transient duration specifically in the DFCs. Current studies are addressing whether embryos dorsalized by inhibition of BMP activity show altered pattern of calcium signaling in the EVL. We anticipate that the GCaMP6s transgenic lines described here offer a valuable addition to the zebrafish toolbox that will enable to visualize many more dynamic calcium events at embryonic and larval stages as well as in adult animals.