The identification of micronucleated chromosomes: a possible assay for aneuploidy.

A technique is presented for establishing the presence of kinetochores in micronuclei (mn) using CREST antikinetochore antibodies and immunofluorescence. In cultured lymphocytes blocked in their second cycle by cytochalasin-B 61% baseline mn possess kinetochores, and thus originated from whole chromosomes. Mn-inducing agents with different modes of action were compared to determine the proportion of mn with kinetochores: virtually all X-ray- and mitomycin-C-induced mn were derived from acentric fragments as shown by the absence of kinetochore immunofluorescence, whereas the majority (79%) of colcemid-induced mn were CREST positive, reflecting the formation of mn through failure of attachment of chromosomes to the spindle. The proportion of mn without kinetochore fluorescence in the control (39%) and colcemid-treated (21%) cultures was greater than expected and possible reasons for this are discussed.