Chromosome instability: from phenotype to genotype and vice versa

Four European laboratories in three consecutive EU projects
under the leadership of Jim Parry developed, compared,
validated and applied a selected number of in vitro and in
vivo tests to assess aneuploidy. Among these the in vitro
cytochalasin B-blocked micronucleus test detects both clastogens
and aneugens and allows discrimination between
induction of acentric chromosome fragments and aneuploidy.
At the present time the test reached the level of full
harmonisation and validation (1) and will be integrated as an
alternative for the in vitro CA test in the battery for hazard
assessment. Moreover, its potential to identify the mechanisms
responsible for clastogenicity/aneugenicity contributed to the
definition of thresholds. The study of apoptosis complemented
the understanding of the importance of chromosome segregation
after exposure to aneugens (2). Jim's prominent position in
science and in regulatory decisions was the motor of this new
approach of risk assessment. Starting from this in vitro
micronucleus assay the methodology was implemented for
human biomonitoring (3). The international HUMN project
defined the scoring criteria and identified the major confounders.
The predictivity of genetic polymorphisms responsible for
activation of xenobiotics and DNA repair on micronuclei
frequencies was determined in human pooled biomonitoring
studies (4; Mateuca et al., submitted for publication). The
predictivity of micronuclei frequencies in PBMCs for human
cancer was demonstrated in European cohort studies (5). To
apply this methodology efficiently, automation of the scoring
procedure was necessary. Therefore the VUB laboratory is
adapting the methodologies for image analysis. One may
consider the micronucleus as a phenotypic marker for early
genetic effects, predictive for cancer. Therefore, we consider
that in combination with genotyping, phenotyping on basis of
micronuclei induction and on basis of in vitro DNA repair
capacity are indispensable biomarkers to be considered.