Calcium signalling is required for anterior patterning in the mouse embryo

Anterior-Posterior axis formation in the mouse embryo requires the active migration of the DVE cell population at E5.5. While intracellular Ca 2+ signalling has been shown to control cell migration in multiple cell contexts, it is unknown whether it is required for DVE migration. The pattern of Ca 2+ activity in the mouse embryo at early peri-implantation stages is also unknown. Using the GCaMP6f Ca 2+ reporter line we performed a detailed assessment of Ca 2+ dynamics between E0.5 – E5.5 using live imaging. We find that prior to implantation, Ca 2+ transients are rare, but at E5.5 widespread, periodic, Ca 2+ transients in extra-embryonic tissues can be observed, including in the VE and ExE. In contrast, cells of the E5.5 epiblast remain relatively quiescent but show sporadic large-scale multi-cellular waves. Inhibition of SERCA at E5.5 abolishes Ca 2+ transients and leads to DVE arrest, indicative that these transients are required for axial patterning. Together these results reveal the pattern of Ca 2+ handling in the early mouse embryo and a novel requirement in anterior-posterior axis formation.