Cooperation between architectural C2H2 proteins in CP190 recruitment to Drosophila regulatory elements

CTCF (CCCTC-binding factor) is the best-studied architectural protein that is highly conserved among animals, including Drosophila and mammals. In Drosophila, CTCF is involved in the organization of functional promoters and insulators, in cooperation with many other architectural proteins, including Su(Hw) and Pita. These proteins, like many other architectural proteins, interact with CP190, which, along with its partners, recruits transcriptional complexes to target promoters. This study was conducted to investigate the cooperation between architectural proteins in the recruitment of CP190 to regulatory elements.

We generated transgenic flies expressing double and triple mutants of dCTCF, Su(Hw), and Pita that cannot interact with CP190. The single mutants are fully viable; however, few triple mutants develop into adults. In the triple mutant, although the CP190 concentration is reduced, the level of gene transcription remains unaltered, suggesting that co-expression of the three mutant proteins is responsible for CP190 instability. ChIP-seq analysis showed that CP190 is required for dCTCF-chromatin binding. In the triple mutant, CP190 demonstrates an almost complete loss of association with the promoters and insulators to which the tested architectural proteins bind; however, these regulatory elements were found to retain their activity.

Architectural proteins cooperate to recruit CP190 to regulatory elements and determine its stability. Despite the important role of CP190 in transcriptional regulation, its functions may be partially performed by partner proteins.