Trichlorfon-induced polyploidy and nondisjunction in mouse oocytes from preantral follicle culture

Trichlorfon (TCF), an organophosphate insecticide and potent inhibitor of choline esterases, was previously shown to induce first meiotic nondisjunction and spindle aberrations in isolated, follicle cell-denuded mouse oocytes maturing in vitro. To explore dose-response and direct and indirect, potentially synergistic effects of TCF on the somatic cells and the oocyte within a follicle, we presently employed preantral follicle culture. 100 microg/ml TCF added at the time of hormonally stimulated resumption of meiosis of follicle cell-enclosed mouse oocytes, 16 h before in vitro ovulation, induced significant rises in first meiotic nondisjunction in oocytes from preantral follicle culture. Lower concentrations (6 microg/ml TCF) disturbed polar body formation. Nuclear maturation to meiosis II in absence of cytokinesis resulted in significant increases in polyploidy. Oocytes maturing in follicles in the presence of TCF had aberrant second meiotic spindles. Influences of TCF on somatic cell function were evident by reduced follicular mucification in vitro and deceased progesterone production. In contrast to TCF, acetylcholine (0.1-100 microM) increased progesterone production. The observations therefore suggest that TCF influences oocyte maturation and folliculogenesis directly and indirectly. High TCF is aneugenic at first meiotic division in oocytes, irrespective of the presence or absence of follicle cells. At lower concentrations TCF interferes with spindle formation, chromosome congression at meiosis II, and coordination of nuclear and cytoplasmic maturation, posing risks for second meiotic errors. The observations suggest that chronic TCF exposure during maturation in the follicle may predispose oocytes to the formation of chromosomally unbalanced preimplantation embryos after fertilization.