THE ROLE OF CA2-INDUCED GERMINAL VESICLE BREAKDOWN OF XENOPUS-LAEVIS OOCYTES - THE SYNERGIC EFFECTS OF MICROTUBULE DEPOLYMERIZATION AND CA2+( IN PROGESTERONE)
Ns. Duesbery et Y. Masui, THE ROLE OF CA2-INDUCED GERMINAL VESICLE BREAKDOWN OF XENOPUS-LAEVIS OOCYTES - THE SYNERGIC EFFECTS OF MICROTUBULE DEPOLYMERIZATION AND CA2+( IN PROGESTERONE), Development, genes and evolution, 206(2), 1996, pp. 110-124
By monitoring Ca-45(2+) influx and efflux from oocytes a transient inc
rease followed by a transient decrease in the Ca2+-content of progeste
rone-treated oocytes was observed. Chelation of intracellular Ca2+ wit
h EGTA or BAPTA-type buffers inhibited progesterone-induced GVBD. Buff
ers with a mid-range K-d (similar to 1.5 mu M) were most effective in
inhibiting GVBD whereas buffers with a K-d above or below this value w
ere less effective. These observations indicate that intracellular C2, probably in the form of a localized release, is required for progest
erone-induced oocyte maturation. However, Ca2+ alone was insufficient
to induce GVBD. When the effects of nocodazole and taxol upon this Ca2
+-requirement were tested, we observed that taxol-induced microtubule
polymerization not only delayed progesterone-induced GVBD but also com
pletely inhibited it in combination with BAPTA-AM. Conversely, nocodaz
ole-induced microtubule depolymerization in combination with ionophore
A23187 not only accelerated progesterone-induced GVBD, but also induc
ed GVBD in the absence of progesterone. The combined treatment of oocy
tes with nocodazole and InsP(3), or with cold microtubule depolymeriza
tion synergistically promote GVBD. In both nocodazole-and cold-treated
oocytes, the GV was displayed to the periphery of the oocytes and und
erwent GVBD when treated with A231187. However, when the GV was displa
ced to the cortex by a centrifugel force under conditions that would n
ot cause microtubule depolymerization and the oocyte was treated with
A231187, oocytes did not undergo GVBD.