Fig. 4. PLC triggers Ca²⁺ oscillations in MII-arrested mouse eggs. (A) Dose-dependent Ca²⁺ oscillations in fura-red loaded mouse eggs triggered by microinjection of cRNA encoding mouse sperm PLC (2 and 0.002 mg/ml, top and middle trace, respectively) and after preincubation with 10 µM cycloheximide (0.02 mg/ml, bottom trace). (B) Mean interspike interval of Ca²⁺ oscillations in eggs following microinjection of various PLC cRNA concentrations (2-0.002 mg/ml in pipette, i.e. <0.1-0.0001 mg/ml in egg) compared with the interval observed upon in vitro fertilisation (IVF). Number of microinjected eggs is shown above each condition. *, significantly different from IVF at the 5% level (Student’s unpaired t-test).