The insulator BEAF32 controls the spatial-temporal expression profile of the telomeric retrotransposon TART in the Drosophila germline.

Insulators are architectural elements implicated in the organization of higher-order chromatin structures and transcriptional regulation. However, it is still unknown how insulators contribute to Drosophila telomere maintenance. Although the Drosophila telomeric retrotransposons HeT-A and TART occupy a common genomic niche, they are regulated independently. TART elements are believed to provide reverse transcriptase activity, whereas HeT-A transcripts serve as a template for telomere elongation. Here, we report that insulator complexes associate with TART and contribute to its transcriptional regulation in the Drosophila germline. Chromatin immunoprecipitation revealed that the insulator complex containing BEAF32, Chriz, and DREF proteins occupy the TART promoter. BEAF32 depletion causes derepression and chromatin changes at TART in ovaries. Moreover, an expansion of TART copy number was observed in the genome of the BEAF32 mutant strain. BEAF32 localizes between the TART enhancer and promoter, suggesting that it blocks enhancer-promoter interactions. Our study found that TART repression is released in the germ cysts as a result of the normal reduction of BEAF32 expression at this developmental stage. We suggest that coordinated expression of telomeric repeats during development underlies telomere elongation control.