MikronukleusTest

The MikronukleusTest, commonly referred to as the micronucleus test, is a genotoxicity assay used to detect chromosomal damage and alterations in the genome. The test measures the formation of small extranuclear bodies, called micronuclei, in cells that have undergone division. It is employed in genetic toxicology to assess the potential of chemicals, drugs, or environmental agents to induce chromosome breakage (clastogenicity) or whole chromosome loss (aneugenicity).

It can be performed in vivo, typically using rodents to evaluate bone marrow or peripheral blood micronuclei, or in vitro with cultured mammalian cells. A separate but related method is the cytokinesis-block micronucleus (CBMN) assay, which uses a cytokinesis inhibitor to distinguish recently divided cells and improves scoring reliability.

Exposure to the test substance is followed by a specified post-exposure period before collecting target cells. Cells are stained and scored for micronuclei under light or fluorescence microscopy, or by automated imaging systems. In CBMN, binucleated cells are specifically scored for micronuclei to reduce confounding by cell division rate and to enable standardized counting.

Positive and negative controls are essential, and results are interpreted in the context of dose response and experimental design. The micronucleus test is standardized by regulatory guidelines, notably OECD test guidelines 474 (in vitro CBMN and other cellular systems) and 487 (in vivo micronucleus in rodents). Limitations include inter-laboratory variability, tissue-specific responses, and the need for expert scoring. The MikronukleusTest remains a core component of the genetic toxicology test battery, informing risk assessment and regulatory decisions.