Representative axial view of the changes in intracellular free calcium during first cell division
of a zebrafish embryo which has been injected with recombinant f-aequorin (a calcium-specific
bioluminescent reporter), and observed using an Imaging Photon Detector. The photon images
(Panels 1-21) represent 30 seconds of accumulated light with a 30 second gap between each image.
Corresponding brightfield images (Panels 0'-18') were grabbed every 3 minutes. It is possible to
see a distinct localized rise in intracellular calcium that accompanies the first appearance of
the furrow arc at the surface of the cell (Panel 2). This is followed by two sub-surface slow
calcium waves which appear to accompany the outward progression of the leading edges of the
furrowing arc (Panels 3-7). As these wave fronts approach the margins of the blastodisc, a more
intense calcium signal appears in the central region (Panel 8); again it moves out to the margins
of the blastodisc (Panels 9 and 10) but it also moves downwards accompanying the deepening of the
furrow as the blastodisc is split in two (Panels 11-15). Eventually, at the end of the first cell
division, the levels of calcium return to around pre-cleavage levels (Panels 18-21).