ATL is required for ER network formation in crude interphase and mitotic extracts. (A and B) Demembranated sperm was added to a crude interphase X. laevis egg extract containing Alexa fluor 488–labeled tubulin and the hydrophobic dye DiIC18. The extract also contained 2 µM of the cytoplasmic fragment of X. laevis ATL2 (cytATL) to inhibit ATL-mediated membrane fusion. Labeled MT asters (A) and ER membranes (B) were visualized by confocal fluorescence microscopy. Bars, 20 µm. (C and D) As in A and B, but with 2 µM of a point mutant of cytATL (cytATL(R232Q)) that does not inhibit fusion. Bars, 20 µm. (E and F) Inhibition of ATL-mediated fusion in mitotic extracts. 2 µM cytATL(R232Q) (E) or cytATL (F) were added to CSF extracts and the membranes were stained with DiIC18. Bars, 10 µm.
