Analyzing Chromosome Function by High Frequency Formation of Dicentric Chromosomes In Vivo

The generation of dicentric chromosomes by site-specific recombination is a technique that has been used to study a number of different chromosomal phenomena, including: (1) the segregation of acentric chromosome fragments (1 ,2 ), (2) the behavior and resolution of chromosome bridges during cell division (3 ,4 ), and (3) cellular responses to a broken chromosome end (4 ). Its greatest advantage is that it allows quantitative experiments on the behavior and cellular consequences of this class of chromosome rearrangement. Furthermore, recombinase-mediated dicentric chromosome formation is specific in that the timing of formation and specification of the chromosomes that are involved are defined by controlled expression of a recombinase and the location of recombinase target sites, respectively. Choice of target sites provides a sophisticated degree of control over the genetic aneuploidy that can result from cell division after a dicentric chromosome is produced. Use of such a predictable, quantitative system can be quite powerful. For example, efficient production of dicentric Y chromosomes aided in the cell cycle analysis of DNA damage responses in Drosophila somatic cells, with significant differences from experiments performed with random (X-ray) methods (4 ).