Originally published as Genetics Published Articles Ahead of Print on January 26, 2009.

Genetics, Vol. 181, 1661-1671, April 2009, Copyright © 2009
doi:10.1534/genetics.108.099093

Expression of I-CreI Endonuclease Generates Deletions Within the rDNA of Drosophila

Silvana Paredes and Keith A. Maggert1

Department of Biology, Texas A&M University, College Station, Texas 77801

1 Corresponding author: Department of Biology, TAMU-3258, Texas A&M University, College Station, TX 77801.
E-mail: kmaggert{at}tamu.edu

The rDNA arrays in Drosophila contain the cis-acting nucleolus organizer regions responsible for forming the nucleolus and the genes for the 28S, 18S, and 5.8S/2S RNA components of the ribosomes and so serve a central role in protein synthesis. Mutations or alterations that affect the nucleolus organizer region have pleiotropic effects on genome regulation and development and may play a role in genomewide phenomena such as aging and cancer. We demonstrate a method to create an allelic series of graded deletions in the Drosophila Y-linked rDNA of otherwise isogenic chromosomes, quantify the size of the deletions using real-time PCR, and monitor magnification of the rDNA arrays as their functions are restored. We use this series to define the thresholds of Y-linked rDNA required for sufficient protein translation, as well as establish the rate of Y-linked rDNA magnification in Drosophila. Finally, we show that I-CreI expression can revert rDNA deletion phenotypes, suggesting that double-strand breaks are sufficient to induce rDNA magnification.