Cytogenetic analysis of mouse oocytes and one-cell zygotes as a potential assay for heritable germ cell aneuploidy

Assays are needed for detecting chemically-induced aneuploidy, for investigating the mechanisms of aneuploidy production, and for obtaining heritable germ cell data that can be used to formulate human risk estimates. In this report, we describe the results of experiments designed to study aneuploidy in metaphase II (MII) oocytes induced by intraperitoneal (i.p.) or oral dosages of colchicine, and to investigate the proportion of aneuploid oocytes transmitted to one-cell (1C) zygotes following oral administration of colchicine immediately following HCG. The proportions (and percentages) of hyperploid MII oocytes were: 1/606 (0.2), 37/504 (7.3), 152/731 (20.8) and 75/319 (23.5) for control, 0.2, 0.3 and 0.4 mg/kg, respectively for i.p. administration of colchicine; and 3/216 (1.4), 8/539 (1.5), 81/511 (15.9), 71/398 (17.8) and 98/391 (25.1) for control, 1.0, 2.0, 3.0 and 4.0 mg/kg, respectively for oral administration of colchicine. The proportions of hyperploid 1C zygotes were 2/327 (0.6), 21/389 (5.4), 62/435 (14.3) and 69/438 (15.8) for control, 2.0, 3.0 and 4.0 mg/kg, respectively for oral colchicine. The proportions of hyperploid MII oocytes and 1C zygotes were significantly higher (Chi-square, P less than 0.01) at each i.p. or oral dose (except 1.0 mg/kg oral) than in the controls. The frequencies of hyperploidy induced by oral doses of colchicine were greater in MII oocytes than in 1C zygotes. We also found that the frequency of developmentally delayed and polyploid 1C zygotes increased with the dose of oral colchicine. Developmentally delayed zygotes contained male-derived chromosomes and female-derived fragmented pronuclei and pronuclei with decondensed chromosomes. These results indicate that higher doses of oral colchicine are needed to induce comparable levels of aneuploidy found after i.p. administration, and that aneuploid oocytes are fertilized and reach first cleavage metaphase. In addition, colchicine induces a spectrum of events including aneuploidy, polyploidy and developmentally delayed oocytes and zygotes.