At the Drosophila bithorax complex many distinct classes of cis-regulatory modules work collectively during development to control gene expression. Abdominal-B (Abd-B) is one of three homeotic genes in the BX-C and is expressed in specific presumptive abdominal segments in the embryo. The transcription of Abd-B is tightly controlled by an array of cis-regulatory modules that direct its expression over extended genomic distances. These regulatory modules include promoters, insulators, silencers, enhancers, promoter targeting sequences and the recently identified promoter tethering element (PTE). To activate gene expression at the endogenous complex, enhancers located >50 kb away must bypass intervening insulators to interact with the Abd-B promoter. The molecular mechanisms that allow enhancers to bypass insulators are not currently well understood. In this short article, we report on a novel mechanism for insulator bypass involving the PTE. In addition, we use bioinformatic analysis across twelve Drosophila genomes to identify putative cis-regulatory sequences that may be capable of facilitating specific promoter-enhancer interactions at the bithorax complex and propose a model for their molecular function during development.

The diverse functional roles for RNA molecules in cells of the developing embryo have been an area of intense study in the last few years. Progress reported at the 49(th) Annual Drosophila Research Conference in San Diego, California highlighted many of the varied mechanistic activities for RNAs. In particular, talks at the 'RNA Biology' platform session provided a great deal of insight into the function of RNA transcripts and their associated protein complexes. The topics covered included: (1) a large-scale screen examining the localization of mRNAs during embryonic development, (2) mechanisms of mRNA transport in different cell types, (3) localization-dependent repression of mRNA translation and (4) the activity of the RNAi machinery in insulator-mediated chromatin structures. Our journey through the modern RNA world clearly indicates that we should be considering a much more expansive role for RNAs in molecular biology.