Microsatellite analysis of recurrent chromosome 2 deletions in acute myeloid leukaemia induced by radiation in F1 hybrid mice

Deletions and/or rearrangements involving one copy of chromosome 2 are consistent and early events in the development of murine acute myeloid leukaemia (AML) by radiation. More than 90% of AMLs induced in the CBA strain of mice express such cytogenetic alterations, with chromosome 2 breakpoints clustering in the C and F regions of the chromosome. In inbred mouse strains, the molecular resolution of these breakpoints is problematic. However, by using x-ray-induced AMLs in F1 progeny of genetically divergent CBA/H x C57B1, it has been possible to show region-specific loss of heterozygosity (LOH) in genetically linked sets of chromosome 2 microsatellite alleles from one of the two parental chromosomes. In the majority of cases, an acceptable concordance was shown for AML chromosome 2 deletion, as defined by microsatellites and as revealed by G-band cytogenetics. A degree of breakpoint clustering was found, but the identification of a number of deletion types, based on the position of proximal and distal breakpoints as defined by microsatellite analysis, strongly supports a leukaemogenic mechanism involving gene deletion. No bias towards loss of CBA or C57B1 alleles was observed, and the gender of AML-presenting animals did not appear to influence the parental origin of the deletions. A molecular map of chromosome 2 breakpoints has now been established in F1 AMLs as a first step towards the molecular cloning of breakpoint sequences.