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A Role for Caenorhabditis elegans COMPASS in Germline Chromatin Organization.
Cells, 9(9).
Deposition of histone H3 lysine 4 (H3K4) methylation at promoters is catalyzed bythe SET1/COMPASS complex and is associated with context-dependent effects on geneexpression and local changes in chromatin organization. The role of SET1/COMPASS inshaping chromosome architecture has not been investigated. Here we usedCaenorhabditis elegans to address this question through a live imaging approach andgenetic analysis. Using quantitative FRET (Förster resonance energy transfer)-basedfluorescence lifetime imaging microscopy (FLIM) on germ cells expressing histoneseGFP-H2B and mCherry-H2B, we find that SET1/COMPASS influences meiotic chromosomeorganization, with marked effects on the close proximity between nucleosomes. Wefurther show that inactivation of set-2, encoding the C. elegans SET1 homologue, orCFP-1, encoding the chromatin targeting subunit of COMPASS, enhances germlinechromosome organization defects and sterility of condensin-II depleted animals.set-2 loss also aggravates germline defects resulting from conditional inactivationof topoisomerase II, another structural component of chromosomes. Expressionprofiling of set-2 mutant germlines revealed only minor transcriptional changes,suggesting that the observed effects are at least partly independent oftranscription. Altogether, our results are consistent with a role for SET1/COMPASSin shaping meiotic chromosomes in C. elegans, together with the non-histone proteinscondensin-II and topoisomerase. Given the high degree of conservation, our findingsexpand the range of functions attributed to COMPASS and suggest a broader role ingenome organization in different species.
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