Micronuclei

Micronuclei are small, extranuclear bodies that form during cell division when chromosome fragments or whole chromosomes fail to be incorporated into the daughter nuclei.

These structures arise from DNA damage, such as double-strand breaks, producing acentric fragments, or from chromosomal mis-segregation during mitosis, leading to lagging chromosomes that are excluded.

Micronuclei can be detected using micronucleus assays. The cytokinesis-block micronucleus (CBMN) assay is widely used for human biomonitoring; cells are treated with a cytokinesis blocker and micronuclei are scored in binucleated cells. Other approaches include the micronucleus assay in exfoliated buccal cells and in peripheral blood lymphocytes.

Micronuclei are indicators of chromosomal instability and genotoxic exposure. They are used to assess the effects of environmental mutagens, radiation, occupational chemicals, and pharmaceuticals. Micronuclei can be categorized into clastogenic micronuclei, arising from acentric chromosome fragments, and aneugenic micronuclei, consisting of whole chromosomes that were not properly segregated.

Interpretation requires caution: micronucleus frequency reflects cumulative damage and repair capacity, not a direct measure of cancer risk alone. Standardization of protocols and scoring criteria is important, and results should be considered with other genotoxicity endpoints.