The influence of cooling on the oranization of meiotic spindle of the mouse oocyte

The effect of cooling on the organization of the microtubulesystem of the mouse oocyte has been investigated. Cooling to25, 18 or 4°C for varying periods of time resulted in aprogressive disassembly of the spindle and the dispersal ofthe chromosomes. The extent of the changes observed was greaterat lower temperatures and with longer periods of exposure. Transferof oocytes from either 37 or 4 to 24°C resulted in the rapidand transient appearance of polar asters and of multiple cytoplasmicasters associated with the pericentriolar material present atthe spindle poles and in the cytocortex of the oocyte. Thistransient aster formation appeared to be driven by the elevatedlevels of free tubulin released during spindle disassembly.An apparent reversal of many of the changes induced by low temperaturewas observed in many but not all oocytes on their restorationto 37°C for 1 h. These results have implications for ourunderstanding of microtubule organization in the oocyte, andfor the handling of oocytes during IVF and GIFT therapeuticprocedures and during the cryopreservation of oocytes.