Increased frequency of multiradial chromosome structures in mouse embryonic fibroblasts lacking functional Werner syndrome protein and poly(ADP-ribose) polymerase-1.

To determine whether the mouse Werner syndrome homologue (Wrn) and the poly (ADP-ribose) polymerase-1 (PARP-1) enzymes act in concert to prevent specific chromosomal rearrangements, mice with a mutation in the helicase domain of the Wrn gene (Wrn(Deltahel/Deltahel) mice) were crossed to PARP-1 null mice. Spectral karyotyping of the mouse metaphases was used in correlation with conventional G-banded karyotype analysis to precisely define the chromosomal aberrations in cells. Although there was no recurrent clonal chromosome aberration, PARP-1 null/Wrn(Deltahel/Deltahel) fibroblasts were distinguished by an increased frequency of chromatid breaks. Interestingly, multiradial structures were the only type of DNA rearrangement that was significantly higher in such PARP-1 null/Wrn(Deltahel/Deltahel) cells. These results indicate that Wrn and PARP-1 enzymes may be part of a protein complex involved in the processing of DNA breaks that can ultimately lead to multiradial structures when both enzymes are nonfunctional. Finally, regions of chromosomes known to be fragile sites in the mouse genome are not more prone to DNA rearrangements in the absence of both PARP-1 and functional Wrn proteins. Moreover, the low number of recurrent rearranged chromosome at any given site suggest a random mutagenesis process in PARP-1 null/Wrn(Deltahel/Deltahel) fibroblasts.