AGE-DEPENDENT INCLUSION OF SEX-CHROMOSOMES IN LYMPHOCYTE MICRONUCLEI OF MAN

Two-color centromeric FISH was used to study the inclusion of the X an d Y chromosomes in micronuclei of cultured lymphocytes from 10 men rep resenting two age groups (21-29 years and 51-55 years). In addition, p an-centromeric FISH was separately performed to identify any human chr omosomes in micronuclei. One hundred micronuclei per probe were examin ed from each donor. A higher mean frequency of Y-positive micronuclei was observed in the older men than in the younger men. In both age gro ups, the X chromosome was micronucleated clearly more often than expec ted by chance, and the Y chromosome was overrepresented in micronuclei among the older men but not among the younger men. In lymphocytes of four women, X-positive micronuclei were more frequent than they were i n men, even after the fact that women have two X chromosomes was taken into account. Similar results were obtained in first-division lymphoc ytes identified by cytochalasin-B-induced cytokinesis block. In compar ison with normal cells, these binucleate cells showed a higher frequen cy (per 1,000 nuclei) of X-positive micronuclei (in the older men) but a lower frequency of micronuclei harboring autosomes or acentric frag ments. In conclusion, the results show that both the X chromosome and the Y chromosome are preferentially micronucleated in male lymphocytes , the Y chromosome only in older subjects. Although the X chromosome h as a general tendency to be included in micronuclei, it is micronuclea ted much more often in women than in men, which is probably the main r eason for the high micronucleus frequency in women that has been docum ented in many previous studies.