Fig. 1.

[Ca²⁺]_ER and [Ca²⁺]_i undergo simultaneous but opposite changes in concentration during oscillations in mouse MII eggs. Ca²⁺ responses were induced by injection of 0.05 μg/μl mouse PLCζ cRNA into MII eggs. In vitro transcribed D1ER RNA was injected into eggs 5 hr before the initiation of [Ca²⁺]_i measurements. The emission ratio of D1ER (YFP/CFP) was used to estimate relative changes in [Ca²⁺]_ER (right axis, blue trace). [Ca²⁺]_i (left axis, red trace) was recorded using Rhod-2. Rhod-2 is generally used to measure mitochondrial Ca²⁺, although given that it fails to target into mitochondria in mouse eggs, it is possible to use it as a reported of [Ca²⁺]_i (Dumollard, R. et al.).