Cytogenetic and genetic studies of radiation-induced chromosome damage in mouse oocytes. I. Numerical and structural chromosome anomalies in metaphase II oocytes, pre- and post-implantation embryos.
The incidences of X-ray induced numerical and structural chromosome anomalies were screened in a range of developmental stages from metaphase II oocytes through to post-implantation embryos. Following 1 Gy of acute X-rays to immediately preovulatory stage oocytes, the rate of hyperploidy (chromosome gain) was found to be elevated over levels in unirradiated controls, at metaphase II, in 1-cell and 3.5 day pre-implantation embryos but not in 8.5 day post-implantation foetuses. In the latter, however, the frequency of mosiacism was significantly increased. A similar response of an increase in mosaicism but not in hyperploidy in 8.5 day post-implantation embryos was also found after irradiation of dictyate stage oocytes with 4 Gy of acute X-rays. Significantly elevated frequencies of structural chromosome anomalies were present in metaphase II oocytes and pre-implantation embryonic stages, but could not be detected in block-stained chromosome preparations from 8.5 day post-implantation foetuses. However, analysis of chromosome preparations after G-banding showed that almost 14% of 14.5 day foetuses carried a chromosome rearrangement after 1 Gy of X-rays to immediately preovulatory stage oocytes. Overall, our data indicate that the presence of radiation-induced chromosome gains are incompatible with embryonic survival but that a proportion of embryos with structural chromosome damage develop past mid-gestation. These latter embryos are therefore potentially capable of contributing to the genetic burden of the next generation.
Tease
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MRC Radiobiology Unit, Chilton, Didcot UK.
Fisher
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D000818:Animals; D002869:Chromosome Aberrations; D047108:Embryonic Development / Q000528:radiation effects; D005314:Embryonic and Fetal Development / Q000528:radiation effects; D005260:Female; D008677:Metaphase; D051379:Mice; D008809:Mice, Inbred C3H; D009630:Nondisjunction, Genetic; D009865:Oocytes / Q000528:radiation effects*; D011247:Pregnancy