Figure 6. MPF is required for ER remodeling during meiosis.

A. Simplified kinase cascade activated during oocyte maturation. Indicated in red is the action of different molecular and pharmacological modulators. The arrow indicates activation and the bar inhibition. B. Confocal fields from individual cells expressing mCherry-KDEL and treated as indicated showing ER structure. After imaging cells were lysed and subjected to Western blotting analysis for phosphor-MAPK (p-M), phosphor-Cdc2 (p-C) and tubullin (Tub) as the loading control (Scale bar, 2 µm). Mos indicates cells injected with Mos RNA, CyR: Cyclin B1 RNA; MOS+Wee: inject Wee1 RNA and incubate cells overnight before Mos RNA injection; CyR+U0126: pre-treat with U0126 (50 µM) for 1 h before Cyclin B1 RNA injection. The effectiveness of these treatments is illustrated in Western blots performed on individual oocytes after confocal imaging. The top band (Tub) represents the tubulin loading control, the middle band phosphorylated MAPK (p-M) and the lower band phosphorylated cdc2 at Tyr-15 (p-C). MAPK phosphorylation indicates its activation, whereas the phosphorylation of Cdc2, the kinase subunit of MPF, indicates its inhibition. C–D. Sensitivity of IP₃-dependent Ca²⁺ release measured as indicated in the text.