Experimental Epidemiology of Chromosome Anomalies : Production of Chromosome Anomalies in Aged Mice

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  • YAMAMOTO Masaharu
    Department of Hygiene and Preventive Medicine, Niigata University School of Medicine

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  • 染色体異常の実験疫学的研究

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Abstract

The study sought to establish an animal model of chromosome anomalies in man. Based on knowledge of reproductive performance in aged mice, an attempt was made to reveal the underlying mechanism of chromosome anomalies. Epidemiologic discipline of this kind may be used to define environmental factors which are responsible to non-disjunction in relation to ageing of the mother. Experimental findings are summarized as follows: 1. A decline of the reproductive performance in aged mice (10 to 16 months-old) was demonstrated. The rate of ovulation was slightly decreased after 10 months of age, but no tendency to decrease was noted in relation to ageing of the mother. An initial reduction in litter-size in aged mice, therefore, was probably due to the embryonic death after 70 M. Yamamoto ovulation. Another finding suggested that the major cause of embryonic loss in aged mice occurred before or during implantation rather than after implantation or during the early organogenesis up to the 10. 5th day of gestation. 2. With advancing age of the female, increased incidence of chromosome aneuploidies was observed among fetuses born to aged mothers. On the other hand, the triploid formations, where a different mechanism was cytologically responsible, was not related to the maternal ageing. Among 12 fetuses with aneuploidies, 8 were mosaics, and 5 out of 12 were litter mates. It is considered that these aneuploid ova were shed together and developed to mosaicism under an unfavourable "milieu interieur" In aged mice. A possible interpretation was proposed for the occurrence of these chromosome anomalies in reference to recent hypotheses for the etiology of chromosome non-disjunction. The author wishes to express his appreciation to Dr. Gen- ichi Watanabe for his advice.

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