Figure 4.

The ER network undergoes tubule-to-sheet conversion during the transition from interphase to meiosis and mitosis. (A) A crude CSF extract was driven into interphase by addition of Ca²⁺ ions. The ER network was stained with the hydrophobic dye DiIC₁₈ and visualized by confocal fluorescence microscopy. Bar, 10 µm. (B) As in A, but the meiotic (CSF) state of the extract was maintained by omitting Ca²⁺. Bar, 20 µm. (C and D) As in B, but with addition of demembranated sperm. C shows the MTs stained with Alexa fluor 488–labeled tubulin, and D shows the membranes stained with DiIC₁₈. Bars, 10 µm. (E) Interphase cytosol, light membranes, and an energy regenerating system were mixed with cyclin BΔ90 to generate a mitotic state. A control was performed with buffer. The membranes were stained with octadecyl rhodamine and visualized by confocal microscopy. The bottom panels show magnified views of the three-way junctions highlighted in the boxed area. Bars: (top) 20 µm; (bottom) 10 µm. (F) The number of three-way junctions in E was counted and expressed as a percentage of the control. The data plotted are the mean ± SD of three independent experiments. ***, P < 0.001, Student’s t test.