CAP-D3, a subunit of Condensin II, regulates expression of Bithorax cluster genes. Kavitha R. Sarvepalli¹, Michelle S. Longworth^1,2. 1) Department of Molecular Genetics, Lerner Research Institute, Cleveland Clinic Foundation, Cleveland, OH, USA; 2) Department of Molecular Medicine, Cleveland Clinic Lerner College of Medicine, Case Western Reserve University, Cleveland, OH, USA.

   Condensin I and II are essential multi-protein complexes that are required for mitotic chromatin condensation. Recent studies have indicated non-canonical roles for Condensin II in inerphase gene regulation. Drosophila Condensin II subunit dCAP-D3 regulates transcription of several clusters of genes. One such cluster is the Bithorax complex (BX-C), which consists of three genes, AbdB, abdA and Ubx that regulate anterior-posterior axis patterning. Maintenance of their expression patterns is regulated epigenetically by the Polycomb group of proteins (PcG). PcG mediate the spread of transcription-repressive chromatin marks across their target genes in a process that is thought to involve chromatin looping. The repressed BX-C locus is known to adopt a higher-order chromatin configuration that stabilizes its repression. However, all of the factors required for this chromatin organization have not been identified. We find that the loss of dCap-D3 expression leads to downregulation of BX-C genes in larval tissues and in S2 cells, by qRT-PCR. Chromatin immunoprecipitation studies reveal that dCAP-D3 is recruited to the Abd-B promoter, suggesting that its action on BX-C genes is direct. As changes in transcription of these genes are accompanied by alterations in the chromatin configuration of the locus, we investigated the chromatin configuration of the BX-C locus in dCap-D3 dsRNA-treated and control (T7 dsRNA-treated) S2 cells by performing chromosome conformation capture assays (3C). Results indicate that long-range interactions between distal DNA elements within the cluster are enhanced upon dCap-D3 knockdown. This suggests that dCAP-D3 has a role in organizing the three-dimensional conformation of BX-C. We hypothesize that dCAP-D3, as part of Condensin II, regulates BX-C by altering its chromatin organization to promote transcription.