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Fig. 6. CamKII acts downstream of the fertilization Ca²⁺ signal. (A) Microinjection of CA-CamKII induces meiotic progression in the absence of Ca²⁺ spiking. Intracellular Ca²⁺ was recorded in eggs induced to complete meiosis by microinjection of cRNA to CA-CamKII (black, n=12) or PLC (grey, n=8). Second polar body (PB2; arrow) and pronucleus (PN; arrowhead) formation are at the times indicated. (B) Eggs were treated with a parthenogenetic stimulus of Sr²⁺ medium but were kept arrested at MetII by KN-93 for a period of 2 hours. CA-CamKII cRNA was then microinjected into eggs. After CA-CamKII injection, eggs exited meiosis but Ca²⁺ spiking was not recovered (n=15). (C) CA-CamKII-induced meiotic progression was not blocked by the Ca²⁺ chelator BAPTA. BAPTA-loaded eggs were either incubated in Sr²⁺-containing medium; or microinjected with CA-CamKII cRNA; or were incubated in Sr²⁺-containing medium followed 2 hours later by CA-CamKII cRNA microinjection. As expected, BAPTA blocked Sr²⁺-induced egg activation but had no inhibitory effect on meiotic progression induced by CA-CamKII, suggesting that the CA-CamKII works downstream of the sperm Ca²⁺ signal. Furthermore, in eggs where BAPTA blocked Sr²⁺-induced meiotic progression, microinjection of CamKII cRNA overcame this block. The number of eggs used is indicated in parenthesis.

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