Chloral hydrate induced spindle aberrations, metaphase I arrest and aneuploidy in mouse oocytes
Abstract
In view of tissue- and sex-specific differences in chemically-induced aneuploidy, we analysed the effects of chloral hydrate (CH) on cell-cycle progression, spindle formation and aneuploidy in in vitro maturing mouse oocytes with cytogenetic and immunofluorescent methods. CH blocks oocyte maturation irreversibly and concentration dependently. During culture in 125 micrograms/ml CH, germinal vesicle breakdown is delayed, and most oocytes become arrested in meiosis I with bivalent chromosomes. Their spindles are asymmetric or attain fusiform poles. Oocytes which progress to metaphase II also possess astral instead of barrel-shaped, anastral spindles as characteristic for the controls. Resolution of chiasmata without polar body extrusion during exposure to 50 and 125 micrograms/ml CH results in significant rises in 'diploid' metaphase II oocytes. Hyperploidy rates do not increase significantly at any concentration of CH, but hypoploidy levels are elevated at 125 micrograms/ml CH. CH induces lagging of chromosomes during telophase I, inhibits spindle elongation in anaphase B and causes chromosome displacement from the spindle equator in metaphase I and II. Oocytes also become irreversibly arrested in maturation when exposed to CH p...Continue Reading
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