Parasegmental (PS)-specific expression of the homeotic genes of the bithorax-complex (BX-C) appears to depend upon the subdivision of the complex into a series of functionally independent cis-regulatory domains. Fab-7 is a regulatory element that lies between iab-6 and iab-7 (the PS11- and PS12-specific cis-regulatory domains, respectively). Deletion of Fab-7 causes ectopic expression of iab-7 in PS11 (where normally only iab-6 is active). Two models have been proposed to account for the dominant Fab-7 phenotype. The first considers that Fab-7 functions as a boundary element that insulates iab-6 and iab-7. The second model envisages that Fab-7 contains a silencer element that keeps iab-7 repressed in parasegments anterior to PS12. Using a P-element inserted in the middle of the Fab-7 region (the bit transposon), we have generated an extensive collection of new Fab-7 mutations that allow us to subdivide Fab-7 into a boundary element and a Polycomb-respond element (PRE). The boundary lies within 1 kb of DNA on the proximal side of the bit transposon (towards iab-6). Deletions removing this element alone cause a complex gain- and loss-of-function phenotype in PS11; in some groups of cells, both iab-6 and iab-7 are active, while in others both iab-6 and iab-7 are inactive. Thus, deletion of the boundary allows activating as well as repressing activities to travel between iab-6 and iab-7. We also provide evidences that the boundary region contains an enhancer blocker element. The Polycomb-response element lies within 0.5 kb of DNA immediately distal to the boundary (towards iab-7). Deletions removing the PRE alone do not typically cause any visible phenotype as homozygotes. Interestingly, weak ectopic activation of iab-7 is observed in hemizygous PRE deletions, suggesting that the mechanisms that keep iab-7 repressed in the absence of this element may depend upon chromosome pairing. These results help to reconcile the previously contradictory models on Fab-7 function and to shed light on how a chromatin domain boundary and a nearby PRE concur in the setting up of the appropriate PS-specific expression of the Abd-B gene of the BX-C.
Development presents... live stream of our Journal Meeting
Watch a session from Development’s Journal Meeting, Unconventional and Emerging Experimental Organisms in Cell and Developmental Biology which was live on the Node Monday 18 September.
Navigating a research career with a disability
Our two recent Perspectives articles explore the lived experiences of disabled scientists in our community. Kelsey L. Anbuhl and colleagues describe the lived experiences of five biologists who share the challenges and successes of undertaking a scientific career with a disability. Whereas Jack Darius Morgan reviews the literature exploring disabled scientists’ experiences in academia.
Focus on regeneration
Tissue regeneration is a fascinating phenomenon, but the cellular and molecular mechanisms underlying regeneration remain incompletely understood. Here, Development has collated a series of articles showcasing some of the most recent advances in regenerative biology.
Keeping up with the Node: Lab meetings
Keep up with the Node 'Lab meeting' posts as the platform regularly highlights development and stem cell biology labs from across the globe and showcases research and researchers from the community. August featured the Nichols lab at the University of Edinburgh, read their 'Lab meeting' article here.
Read & Publish Open Access publishing: what authors say
We have had great feedback from authors who have benefitted from our Read & Publish agreement with their institution and have been able to publish Open Access with us without paying an APC. Read what they had to say.
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