Chromatin Insulator Function and Nuclear Organization

National Institute Of Diabetes And Digestive And Kidney Diseases

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Abstract

The transcription factor M1BP cooperates with CP190 to activate transcription at TAD borders and promote chromatin insulator activity Organization of the genome is driven by forces affecting transcriptional state, but the relationship between transcription and the machinery controlling genome architecture remains unclear. We identified the Drosophila transcription factor Motif 1 Binding Protein (M1BP) in physical association with the gypsy chromatin insulator core complex, including the universal insulator protein CP190. M1BP is required for enhancer-blocking and barrier activities of the gypsy insulator as well as its proper nuclear localization. Genome-wide, M1BP specifically colocalizes with CP190 at Motif 1-containing promoters, which are enriched at topologically associating domain (TAD) borders. M1BP is required for CP190 chromatin binding at many shared sites, and CP190 also affects M1BP chromatin association. Importantly, both factors are required for Motif 1-dependent gene expression and to promote transcriptional activation near TAD borders genome-wide. Our results reveal physical and functional interaction between CP190 and M1BP to activate transcription at TAD borders and mediate chromatin insulator-dependent genome organization. Oligopaint DNA FISH reveals telomere-based meiotic pairing dynamics in the silkworm, Bombyx mori Accurate chromosome segregation during meiosis is essential for reproductive success. Yet, many fundamental aspects of meiosis remain unclear, including the mechanisms regulating homolog pairing across species. This gap is partially due to our inability to visualize individual chromosomes during meiosis. We employed Oligopaint FISH to investigate homolog pairing and compaction of meiotic chromosomes and resurrect a classical model system, the silkworm Bombyx mori. Our Oligopaint design combines multiplexed barcoding with secondary oligo labeling for high flexibility and low cost. These studies illustrate that Oligopaints are highly specific in whole-mount gonads and on meiotic squashes. We showed that meiotic pairing is robust in both males and females and that pairing can occur through numerous partially paired intermediate structures. We also showed that pairing in male meiosis occurs asynchronously and seemingly in a transcription-biased manner. Further, we revealed that meiotic bivalent formation in B. mori males is highly similar to bivalent formation in C. elegans, with both of these pathways ultimately resulting in the pairing of chromosome ends with non-paired ends facing the spindle pole. Additionally, microtubule recruitment in both C. elegans and B. mori is likely dependent on kinetochore proteins but independent of the centromere-specifying histone CENP-A. Finally, using super-resolution microscopy in the female germline, we showed that homologous chromosomes remain associated at telomere domains in the absence of chiasma and after breakdown and modification to the synaptonemal complex in pachytene. These studies reveal novel insights into mechanisms of meiotic homolog pairing both with or without recombination.