Boundary bypass activity in the region of the bithorax complex is position dependent and regulated.

Expression of () in abdominal segments A5A8 is controlled by four regulatory domains, . Each domain has an initiator element (which sets the activity state), elements that maintain this state and tissue-specific enhancers. To ensure their functional autonomy, each domain is bracketed by boundary elements (, , and ).

Boundary Bypass Activity in the Region of the Bithorax Complex is Position Dependent and Regulated.

Unlabelled: Expression of ( ) in abdominal segments A5 A8 is controlled by four regulatory domains, . Each domain has an initiator element (which sets the activity state), elements that maintain this state and tissue-specific enhancers. To ensure their functional autonomy, each domain is bracketed by boundary elements ( , , and ).

Redundant enhancers in the iab-5 domain cooperatively activate Abd-B in the A5 and A6 abdominal segments of Drosophila.

The Abdominal-B (Abd-B) gene belongs to the bithorax complex and its expression is controlled by four regulatory domains, iab-5, iab-6, iab-7 and iab-8, each of which is thought to be responsible for directing the expression of Abd-B in one of the abdominal segments from A5 to A8. A variety of experiments have supported the idea that BX-C regulatory domains are functionally autonomous and that each domain is both necessary and sufficient to orchestrate the development of the segment they specify. Unexpectedly, we discovered that this model does not always hold.

Drosophila architectural protein CTCF is not essential for fly survival and is able to function independently of CP190.

CTCF is the most likely ancestor of proteins that contain large clusters of C2H2 zinc finger domains (C2H2) and is conserved among most bilateral organisms. In mammals, CTCF functions as the main architectural protein involved in the organization of topology-associated domains (TADs). In vertebrates and Drosophila, CTCF is involved in the regulation of homeotic genes.

Mapping of functional elements of the Fab-6 boundary involved in the regulation of the Abd-B hox gene in Drosophila melanogaster.

The autonomy of segment-specific regulatory domains in the Bithorax complex is conferred by boundary elements and associated Polycomb response elements (PREs). The Fab-6 boundary is located at the junction of the iab-5 and iab-6 domains. Previous studies mapped it to a nuclease hypersensitive region 1 (HS1), while the iab-6 PRE was mapped to a second hypersensitive region HS2 nearly 3 kb away.

The insulator functions of the polydactyl C2H2 zinc finger protein CTCF: Necessity versus sufficiency.

In mammals, a C2H2 zinc finger (C2H2) protein, CTCF, acts as the master regulator of chromosomal architecture and of the expression of Hox gene clusters. Like mammalian CTCF, the homolog, dCTCF, localizes to boundaries in the bithorax complex (BX-C). Here, we have determined the minimal requirements for the assembly of a functional boundary by dCTCF and two other C2H2 zinc finger proteins, Pita and Su(Hw).

Complete reconstitution of bypass and blocking functions in a minimal artificial insulator from complex.

Boundaries in the complex (BX-C) delimit autonomous regulatory domains that drive parasegment-specific expression of the genes , and The boundary is located between the and domains and has two key functions: blocking cross-talk between these domains and at the same time promoting communication (boundary bypass) between and the promoter. Using a replacement strategy, we found that multimerized binding sites for the architectural proteins Pita, Su(Hw), and dCTCF function as conventional insulators and block cross-talk between the and domains; however, they lack bypass activity, and is unable to regulate Here we show that an ∼200-bp sequence of dHS1 from the boundary rescues the bypass defects of these multimerized binding sites. The dHS1 sequence is bound in embryos by a large multiprotein complex, Late Boundary Complex (LBC), that contains the zinc finger proteins CLAMP and GAF.

Boundaries mediate long-distance interactions between enhancers and promoters in the Drosophila Bithorax complex.

Drosophila bithorax complex (BX-C) is one of the best model systems for studying the role of boundaries (insulators) in gene regulation. Expression of three homeotic genes, Ubx, abd-A, and Abd-B, is orchestrated by nine parasegment-specific regulatory domains. These domains are flanked by boundary elements, which function to block crosstalk between adjacent domains, ensuring that they can act autonomously.

The bithorax complex iab-7 Polycomb response element has a novel role in the functioning of the Fab-7 chromatin boundary.

Expression of the three bithorax complex homeotic genes is orchestrated by nine parasegment-specific regulatory domains. Autonomy of each domain is conferred by boundary elements (insulators). Here, we have used an in situ replacement strategy to reanalyze the sequences required for the functioning of one of the best-characterized fly boundaries, Fab-7.