Condensin II inhibits heterochromatic gene silencing and facilitates transposon silencing. Maureen Peterson¹, Christopher Bauer², John Manak³, Stephen Butcher³, Giovanni Bosco¹. 1) Genetics, Dartmouth College, Hanover, NH; 2) New York University Center for Genomics and Systems Biology; 3) University of Iowa Department of Biology.

   Condensin II is a protein complex well studied for its role in mitotic chromosome condensation. However, its presence in the nucleus throughout the cell cycle indicates that condensin II may perform important functions in interphase as well. To investigate possible gene regulatory roles of condensin II, we used genomic tiling arrays to compare transcript levels in stage 10 egg chambers of wildtype and condensin II mutant flies. We found that genes located within heterochromatin are repressed in condensin II mutants, which we confirmed using qRT-PCR analysis. We also found that piRNA clusters, sequences found near heterochromatin and known to regulate transposable element transcript levels, are similarly repressed in condensin II mutants. Consistent with their role in regulation of transposons, we find that transposable element transcript levels are increased in condensin II mutants. Investigation of genomic copy number of overexpressed transposable elements by qPCR revealed that some classes of transposable elements are increased in copy number in the germline of condensin II mutants. This finding raises the possibility that transposons are actively jumping in mutant flies. We also show that localization of heterochromatin protein 1 (HP1) is perturbed in the nurse cells of condensin II mutants. We propose two possible models describing how aberrant localization of HP1 may result in hypersilencing of heterochromatic genes and, indirectly, transposon transcript levels.