Comparative in vitro cytogenetic studies in mercury-exposed human lymphocytes

As part of a long-term cytogenetic research project on mercury, we studied the in vitro clastogenic capacity of HgCl2 and CH3HgCl as well as their influence on chromosome segregation by means of a computer-aided chromosome distribution study in metaphase plates. As in other in vitro studies published elsewhere, we exposed human peripheral blood lymphocytes to different concentrations of the mercury compound during a limited period of the pre-DNA synthetic stage (G1-S) or from that stage up to mitosis (G1-M). For both exposure periods and both mercury compounds we observed a rather important clastogenic effect as well as a dissociation of the (normally highly associated) acrocentrics. The results do indicate, in conjunction with previously published data, that mercury compounds alter the chromosome segregation at lower concentrations than those observed for clastogenicity. Moreover, the effects on chromosome segregation are not necessarily due to binding to spindle proteins. Binding to--and inactivation of RNA polymerase I may for example be another mechanism of action which is more important for the inorganic form of mercury than for the organic form.