PARTHENOGENETIC ACTIVATION OF CHINESE-HAMSTER OOCYTES BY CHEMICAL STIMULI AND ITS CYTOGENETIC EVALUATION

This study was undertaken parthenogenetically to activate Chinese hams ter oocytes in vitro by chemical stimuli. Oocytes were exposed to five different chemical agents, ethanol (EtOH), strontium chloride (SrCl2) , cycloheximide (CHX), phorbol ester (PMA), and ionophore A23187 (IA23 ). No parthenogenetic activation was observed in the oocytes treated w ith 8% EtOH for 8-11 min, 1.7 mM and 5.0 mM SrCl2 for 1 hr, 100 mu M a nd 400 mu M CHX for 2 hr, and 81 nM and 162 nM PMA for 5 min. In contr ast, 89.7% of oocytes parthenogenetically extruded the second polar bo dy in treatment with 3 mu M IA23 for 5 min, but only 22.6% of them for med a pronucleus and developed to 2-cell embryos. The remaining ova st opped their cell cycle immediately after completion of the second meio tic division. They had unichromatid chromosomes (monads), which are ca lled MIII chromosomes. Treatment with 5 mu M IA23 for 5 min was so del eterious that >90% of oocytes were degenerated. However, oocyte activa tion was significantly improved when the treatment with 3 mu M IA23 fo r 5 min was followed by treatment with 8% EtOH for 10 min, 100 mu M CH X for 2 hr, 81 nM PMA for 5 min or 3 mu M IA23 for 5 min: rates of pro nuclear formation were 54.4%, 84.3%, 34.2%, and 54.6%, respectively. M ore than 80% of pronucleate ova successfully developed into 2-cell sta ge. Additive treatment with 5 mN SrCl2 for 1 hr had no positive effect on pronuclear formation. Incidences of aneuploidy (4.6%) and structur al chromosome aberrations (1.0%) in parthenogenons produced by combine d stimuli of IA23 and CHX were not significantly different from those (3.8% and 1.6%, respectively) in female pronuclei of ova fertilized in vitro, showing that combined treatments with IA23 and CHX cause neith er nondisjunction at the second meiotic division nor structural aberra tions in MII chromosomes. The present technique for parthenogenetic ac tivation of Chinese hamster oocytes may be useful as an assessment sys tem to detect aneugenic and clastogenic effects of mutagens on mammali an oocytes. (C) 1997 Wiley-Liss, Inc.