Fig. 2. Ca²⁺ wave pacemakers in eggs. (A) A sequence showing a Ca²⁺ wave initiated by the meiosis II pacemaker (MII PM) in the vegetal pole (v) of a mouse egg injected with sperm extracts. The second polar body is visible in the animal pole (a). (B) A sequence showing two examples of fertilized ascidian eggs displaying Ca²⁺ waves initiated by the MII calcium wave pacemaker located in the vegetal contraction pole (MII PM). (C) Two examples of a UV flash releasing cgPtdIns(4,5)P₂ applied between two waves, the fertilized ascidian eggs respond by eliciting a wave from the animal pole of the egg (artPM). (D) The distribution of ER and mitochondria in the contraction pole (cp). A layer of cortical ER in the cortical most layer can be seen (in red) juxtaposed to the mitochondria-rich sub-cortical region (in green). (E) Schematic representation of the contraction pole showing the microvillated plasma membrane, microfilaments (in blue), as well as the ER-rich domains in the cortex (red) and the mitochondria-rich subcortical domain (green). (F) Calcium Green/Texas Red ratiometric image of [Ca²⁺]_c, showing the initiation of a Ca²⁺ wave elicited by the MII pacemaker in the contraction pole.