Preprint: shared Su(Hw) binding sites mediate specific TAD boundary interactions in Drosophila

A preprint deposited on bioRxiv on 31 May 2026 investigates how topologically associating domain (TAD) boundaries establish specific, orientation-dependent interactions in Drosophila chromatin. The work focuses on Su(Hw), a zinc-finger protein that binds the gypsy retrotransposon and is known to act as an insulator, and asks how shared Su(Hw) binding sites at TAD boundaries mediate physical contacts between those boundaries.

Loop extrusion — the leading mechanistic model for TAD formation in vertebrates — has been shown to be insufficient to explain TAD formation in Drosophila, leaving a significant gap in the understanding of chromosomal architecture across eukaryotes. The preprint presents evidence that Su(Hw) binding site sharing generates the specificity and directionality of inter-TAD interactions, offering a candidate mechanism to fill that gap.

The work is a preprint and has not yet undergone peer review. Researchers working in chromosome biology, genome organisation, and Drosophila genetics will find the molecular detail of most direct relevance. Educators and students covering 3D genome organisation and insulator function may also find this a useful primary source example. Full methods, datasets, and conclusions should be verified against the peer-reviewed version once published.