Figure 1. ER remodeling and IP₃ receptor clustering during meiosis.

A. Functional clustering of elementary Ca²⁺ release events during oocyte maturation. Xenopus oocytes were injected with 10 µM caged IP₃ and 40 µM Oregon-green. Oocyte maturation was induced with progesterone and both immature oocytes and fully mature eggs were imaged in linescan mode at 488 nm with the 405 nm laser at low intensity (0.2%) to continuously uncage cIP₃. The same region in the cell was scanned continuously in linescan mode with the x-axis representing time and the y-axis space. The single isolated Ca²⁺ puffs observed in the oocyte coalesce into larger release events referred to as single release events (SRE). B. The ER remodels during oocyte maturation to form large patches in the egg. Oocytes were injected with GFP-IP₃ receptor (IP₃R) (50 ng/cell) and mCherry-KDEL (10 ng/cell). Images show the formation of ER patches in both animal and vegetal hemisphere to which IP₃ receptors localize (Scale bar, 2 µm). C. Frequency of ER patches on the animal and vegetable poles (n = 166; 14 frogs). D. ER patch density and area (n = 38). E. Width of elementary Ca²⁺ release events in the egg as compared to the width of ER patches.