CytokinesisBlock

Cytokinesis block refers to laboratory techniques that inhibit cytokinesis, the division of the cytoplasm, while allowing karyokinesis to proceed. The result is binucleated cells that have undergone one mitotic division but have not completed cytokinesis.

The most common blockers are cytochalasin B and related compounds, which bind to actin filaments and prevent the formation of the contractile ring required for cytokinesis. By interrupting cytokinesis, cells become binucleated, a state exploited in genotoxicity assays that measure chromosomal damage.

A major application is the cytokinesis-block micronucleus (CBMN) assay. In this approach, cultured cells are exposed to a test agent, then cytochalasin B is added to block cytokinesis during subsequent cell cycles. After incubation, cells are fixed and stained, and binucleated cells are scored for the presence of micronuclei, small extranuclear bodies that reflect DNA damage such as chromosome fragments or whole chromosomes.

Interpretation of CBMN results uses the frequency of micronuclei in binucleated cells as an index of genotoxic potential. The assay can help distinguish clastogenic (chromosome breakage) and aneugenic (whole-chromosome loss) effects when used alongside complementary cytogenetic analyses.

Limitations include the need for optimization across cell types, potential cytotoxic effects of cytochalasin B, and the subjective nature of scoring. The method is most informative for mechanisms leading to micronucleus formation and is not universally applicable to all genotoxic endpoints.