Cooperation between Caenorhabditis elegans COMPASS and condensin in germline chromatin organization

Abstract Background Histone-modifying activities play important roles in gene expression and influence higher-order genome organization. SET1/COMPASS (Complex Proteins Associated with Set1) deposits h istone H3 lysine 4 (H3K4) methylation at promoter regions and is associated with context-dependent effects on gene expression. Whether it also contributes to higher-order chromosome organization has not been explored. Results Using a quantitative FRET (Förster resonance energy transfer)-based fluorescence lifetime imaging microscopy (FLIM) approach to assay nanometer scale chromatin compaction in live animals, we reveal a novel role for SET1/COMPASS in structuring meiotic chromosomes in the C. elegans germline . Inactivation of SET-2, the C. elegans homologue of SET1, strongly enhanced chromosome organization defects and loss of fertility resulting from depletion of condensin-II, and aggravated defects in chromosome morphology resulting from inactivation of topoisomerase II, another major structural component of chromosomes. Loss of CFP-1, the chromatin targeting subunit of COMPASS, similarly affected germline chromatin compaction measured by FLIM-FRET and enhanced condensin-II knock-down phenotypes. Conclusions The data presented here are consistent with a role of SET1/ COMPASS in shaping meiotic chromosomes in the C. elegans germline. This new insight has important implications for how c hromatin-modifying complexes and histone modifications may cooperate with non histone-proteins to achieve proper chromosome organization, not only in meiosis, but also in mitosis.