SUMMARY Eukaryotic chromosomes are partitioned into topologically associating domains (TADs) that are demarcated by distinct insulator-binding proteins (IBPs) in Drosophila. Whether IBPs regulate specific long-range contacts and how this may impact gene expression remains unclear. Here we identify ‘indirect peaks’ of multiple IBPs, that represent their distant sites of interactions through long-range contacts. Indirect peaks depend on protein-protein interactions among multiple IBPs and their common co-factors, including CP190, as confirmed by high-resolution analyses of long-range contacts. Mutant IBPs unable to interact with CP190 impair long-range contacts as well as the expression of hundreds of distant genes that are specifically flanked by indirect peaks. Regulation of distant genes strongly correlates with RNAPII pausing, highlighting how this key transcriptional stage may trap insulator-based long-range interactions. Our data illustrate how indirect peaks may decipher gene regulatory networks through specific long-range interactions.

Abstract:The toxicity of the nonaggregated amyloid ␤-peptide (1-40) [A␤(1-40)] on the viability of rat cortical neurons in primary culture was investigated. We demonstrated that low concentrations of A␤ peptide, in a nonfibrillar form, induced a time-and dose-dependent apoptotic cell death, including DNA condensation and fragmentation. We compared the neurotoxicity of the A␤(1-40) peptide with those of several A␤-peptide domains, comprising the membrane-destabilizing C-terminal domain of A␤ peptide (e.g., amino acids 29 -40 and 29 -42). These peptides reproduced the effects of the (1-40) peptide, whereas mutant nonfusogenic A␤ peptides and the central region of the A␤ peptide (e.g., amino acids 13-28) had no effect on cell viability. We further demonstrated that the neurotoxicity of the nonaggregated A␤ peptide paralleled a rapid and stable interaction between the A␤ peptide and the plasma membrane of neurons, preceding apoptosis and DNA fragmentation. By contrast, the peptide in a fibrillar form induced a rapid and dramatic neuronal death mainly through a necrotic pathway, under our conditions. Taken together, our results suggest that A␤ induces neuronal cell death by either apoptosis and necrosis and that an interaction between the nonfibrillar C-terminal domain of the A␤ peptide and the plasma membrane of cortical neurons might represent an early event in a cascade leading to neurodegeneration. Key Words: Alzheimer's disease -Amyloid ␤-peptideApoptosis-Fusogenic peptides-Neurotoxicity-Cortical primary neurons.