Induction of a whole chromosome loss by colcemid in human cells elucidated by discrimination between FISH signal overlap and chromosome loss

• We report numerical changes of a chromosome using whole chromosome FISH.
• We demonstrate that colcemid induces an actual whole chromosome loss in human cells.
• Chromosome loss can be distinguished from overlapping signals by FISH signal intensity.

Aneuploidy is a change in the number of chromosomes and an essential component in tumorigenesis. Therefore, accurate and sensitive detection of aneuploidy is important in screening for carcinogens. In vitro micronucleus (MN) assay has been adopted in the recently revised International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) S2 guideline and can be employed to predict both clastogenic and aneugenic chromosomal aberrations in interphase cells. However, distinguishing clastogens and aneugens is not possible using this assay. The Organization for Economic Co-operation and Development (OECD) guideline TG487 therefore recommends the use of centromere/kinetochore staining in micronuclei to differentiate clastogens from aneugens. Here, we analyzed numerical changes of a specific chromosome in cytokinesis-blocked binucleated cells by fluorescence in situ hybridization (FISH) using the specific centromere probe in human lymphoblastoid TK6 cells treated with aneugens (colcemid and vincristine) or clastogens (methyl methanesulfonate [MMS] and 4-nitroquinoline-1-oxide [4-NQO]). Colcemid and vincristine significantly increased the frequencies of nondisjunction and loss of FISH signals, while MMS and 4-NQO slightly increased only the frequency of loss of FI