Visualization of Transvection in Living Drosophila Embryos

• Published in: Molecular cell 2018-04, Vol.70 (2), p.287-296.e6
• Main Authors: Lim, Bomyi, Heist, Tyler, Levine, Michael, Fukaya, Takashi
• Format: Article
• Language: English
• Subjects: alleles; Animals; Animals, Genetically Modified; chromosomal loop domains; chromosomes; Drosophila; Drosophila embryos; Drosophila melanogaster - embryology; Drosophila melanogaster - genetics; Drosophila melanogaster - metabolism; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Embryo, Nonmammalian - metabolism; Enhancer Elements, Genetic; enhancers; Gene Expression Regulation, Developmental; Genes, Reporter; insulators; live imaging; Recombinant Proteins - genetics; Recombinant Proteins - metabolism; reporter genes; RNA Polymerase II - genetics; RNA Polymerase II - metabolism; TADs; Time Factors; transcription; transcription (genetics); Transcription Factors - genetics; Transcription Factors - metabolism; Transcriptional Activation; transvection
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2018.02.029

How remote enhancers interact with appropriate target genes persists as a central mystery in gene regulation. Here, we exploit the properties of transvection to explore enhancer-promoter communication between homologous chromosomes in living Drosophila embryos. We successfully visualized the activation of an MS2-tagged reporter gene by a defined developmental enhancer located in trans on the other homolog. This trans-homolog activation depends on insulator DNAs, which increase the stability—but not the frequency—of homolog pairing. A pair of heterotypic insulators failed to mediate transvection, raising the possibility that insulator specificity underlies the formation of chromosomal loop domains. Moreover, we found that a shared enhancer co-activates separate PP7 and MS2 reporter genes incis and intrans. Transvecting alleles weakly compete with one another, raising the possibility that they share a common pool of the transcription machinery. We propose that transvecting alleles form a trans-homolog “hub,” which serves as a scaffold for the accumulation of transcription complexes. [Display omitted] •Insulators increase the stability, but not the frequency, of allele-allele pairing•The gypsy insulator functions in an orientation-independent manner•A shared enhancer co-activates linked PP7 and MS2 reporter genes in cis and in trans•Linked reporter genes compete for shared resources during transvection Lim et al. explore a process called transvection in living Drosophila embryos, whereby enhancers on one homolog activate transcription units on the other homolog. They show that insulators facilitate transvection by stabilizing allele-allele pairing. Surprisingly, a shared enhancer coactivates a cis-linked PP7 reporter gene along with a trans-linked MS2 reporter contained on the other homolog. This coactivation is consistent with emerging evidence for transcription “hubs” containing clusters of RNA polymerase II and associated activators.