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Genetics. 2019 Sep 24. pii: genetics.302694.2019. doi: 10.1534/genetics.119.302694. [Epub ahead of print]

Distinct Elements Confer the Blocking and Bypass Functions of the Bithorax Fab-8 Boundary.

Author information

1
Institute of Gene Biology Russian Academy of Sciences.
2
Princeton University.
3
Russian Academy of Sciences.
4
Institute of Gene Biology Russian Academy of Sciences; Princeton University pschedl@princeton.edu.

Abstract

Boundaries in the Drosophila bithorax complex (BX-C) enable the regulatory domains that drive parasegment specific expression of the three Hox genes to function autonomously. The four regulatory domains (iab-5, iab-6, iab-7 and iab-8) that control the expression of the Abdominal-B (Abd-B) gene are located downstream of the transcription unit and are delimited by the Mcp, Fab-6, Fab-7 and Fab-8 boundaries. These boundaries function to block crosstalk between neighboring regulatory domains. In addition, three of the boundaries (Fab-6, Fab-7 and Fab-8) must also have bypass activity so that regulatory domains distal to the boundaries can contact the Abd-B promoter. In the studies reported here, we have undertaken a functional dissection of the Fab-8 boundary using a boundary replacement strategy. Our studies indicate that the Fab-8 boundary has two separable sub-elements. The distal sub-element blocks crosstalk, but can not support bypass. The proximal sub-element has only minimal blocking activity but is able to mediate bypass. A large multiprotein complex, the LBC, binds to sequences in the proximal sub-element and contributes to its bypass activity. The same LBC complex has been implicated in the bypass activity of the Fab-7 boundary.

KEYWORDS:

Abdominal-B; Bithorax; CTCF; Fab-7; Fab-8; LBC; blocking; bypass; chromatin boundaries; insulators

PMID:
31551239
DOI:
10.1534/genetics.119.302694
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