Rise of intracellular Ca2+ level causes the decrease of cyclin B1 and Mos in the newt eggs at fertilization.
Unfertilized eggs of the newt, Cynops pyrrhogaster, are arrested at the second meiotic metaphase, with activity of the M-phase promoting factor (MPF) maintained at a high level. After fertilization, the eggs resume the cell cycle, and emit the second polar body. When the change in [Ca2+]i in the fertilized eggs was monitored by aequorin, an early increase in [Ca2+]i was observed 5-10 min after insemination and continued for about 30 sec. A late increase in [Ca2+]i then occurred 10-15 min after fertilization and continued for 30-40 min. The injection of 1,2-Bis (2 aminophenoxy) ethane-N,N,N',N',-tetraacetic acid (BAPTA) into unfertilized eggs inhibited reinitiation of the cell cycle after fertilization. Western blot analysis with antibodies against cyclin B1 or Mos indicated that both cyclin B1 and Mos were present in unfertilized eggs, but both disappeared within 30 min after fertilization. Treatment with Ca2+-ionophore decreased both cyclin B1 and Mos. Chymotryptic activity in Cynops egg extracts was not significantly increased after fertilization or activation by treatment with the Ca2+-ionophore. No change in [Ca2+]i was observed following treatment with cycloheximide, but the amount of both cyclin B1 and Mos rapidly decreased. These results indicate that resumption of meiosis in Cynops eggs is induced by an increase in [Ca2+]i at fertilization, which causes degradation of both cyclin B1 and Mos by inhibition of de novo synthesis of those proteins.
Yamamoto
S
S
Department of Biological Science, Faculty of Science, Yamaguchi University, Japan.
Yamashita
M
M
Iwao
Y
Y
D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002918:Chymotrypsin / Q000378:metabolism; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D003513:Cycloheximide / Q000494:pharmacology; D005306:Fertilization; D007424:Intracellular Fluid / Q000378:metabolism; D007476:Ionophores / Q000494:pharmacology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D017231:Proto-Oncogene Proteins c-mos / Q000378:metabolism*; D012455:Salamandridae; D015053:Zygote / Q000187:drug effects / Q000378:metabolism*
D019926:Cyclin B; D056744:Cyclin B1; D007476:Ionophores; D011500:Protein Synthesis Inhibitors; D000001:Calcimycin; D003513:Cycloheximide; D017231:Proto-Oncogene Proteins c-mos; D002918:Chymotrypsin; D002118:Calcium