ChIP-seq and data from Drosophila melanogaster cell line Kc167 in different osmostress conditions.

Chromatin is organized into a 3D interwoven tapestry of multi-layer architectural features important for controlling gene expression. How distinct layers influence each other and quickly they quickly they respond to cellular environment is unclear. Using Hi-C in Drosophila melanogaster, we measure how 3D chromatin organization responds to cellular hyperosmotic stress. In combination with the hd-pairing method, we demonstrate that chromosome unpairing represents a fast an reversible response to hyperosmotic stress. We identify a novel function of the Z4 protein as an anti-pairer, which we demonstrate is necessary for changes to chromatin organization during hyperosmotic stress. Finally, we demonstrate how changes to pairing impacts the other interwoven layers of 3D chromatin organization. Overall design: First set of ChIP-seq data is from LacZ Isotonic immunoprecipitated with CAP-H2 antibody, LacZ Osmostress with CAP-H2 and Z4 antibodies, and Z4KD Isotonic with CAP-H2 antibody. Each group has 2 replicates. Second set of ChIP-seq data is from LacZ Osmostress and Z4KD immunoprecipitated with RNAPII antibody. Each group has 2 replicates.