FISH: Differentiation between aneugens and clastogens in in vitro micronucleus tests

FISH methodology

In in vitro micronucleus tests (according to OECD 487), the occurrence of micronuclei in interphase cells provides an indirect, but easy and rapid measurement of structural chromosomal damage (clastogenicity) and effects on the spindle apparatus (aneugenicity) in cells that have undergone cell division during or after exposure to a test substance. Micronuclei arise from chromosomal fragments or whole chromosomes, occur rarely spontaneously, but are induced by clastogenic or aneugenic agents.

To discriminate between the two mechanisms, which lead to the induction of micronuclei, the method of Fluorescence In Situ Hybridisation (FISH) with a centromere specific probe can be used. By assessment of centromere negative micronuclei as readout for clastogenic events or centromere positive micronuclei as readout for aneugenic events, the dominant mechanism can be determined.

Regulatory authorities are increasingly demanding that positive results from in vitro micronucleus tests are assessed to determine the mechanism of micronuclei induction. The mechanism is crucial for the regulatory assessment of the observation. We can now support you with validated FISH methodology to provide this assessment.