Cyclophosphamide-induced aberrations of chromosome pairing in pachytene oocytes

The aim of this study was to characterise damage to synaptonemal complexes in oocytes following cyclophosphamide exposure. Pregnant mice were treated with three different doses of cyclophosphamide (10, 30 and 50 mg/kg body weight) at day 13 of gestation, when oogonia and very early meiotic cells in the female fetuses are found. Primary oocytes were analysed by light- and electron microscopy at gestational day 17 to reveal effects of the alkylating agent on the chromosomal pairing behaviour. Our pachytene analysis demonstrated that the fraction of cells with lesions of synaptonemal complexes, partial asynapsis and desynaptic bivalents were significantly increased over the levels in the control group. The frequency of alterations was similar at doses of 30 and 50 mg/kg. In addition, a significant increase in frequency of univalents over the base level became evident, showing the highest incidence on a dose of 50 mg/kg.