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ABSTRACT
Polycomb group (PcG) and Trithorax group (TrxG) proteins orchestrate development of a multicellular organism by faithfully maintaining cell fate decisions made early in embryogenesis. An important chromatin mark connected to PcG/TrxG regulation is bivalent domains, the simultaneous presence of H3K27me3 and H3K4me3 on a given locus, originally identified in mammalian embryonic stem cells but considered to be absent in invertebrates. Here, we provide evidence for the existence of bivalency in fly embryos. Using a recently described PcG reporter fly line, we observed a strong reporter inducibility in the embryo and its sharp decrease in larval and adult stages. Analysis of the chromatin landscape of the reporter revealed a strong signal for the repressive PcG mark, H3K27me3, in all three developmental stages and, surprisingly, a strong signal for a transcriptionally activating H3K4me3 mark in the embryo. Using re-chromatin immunoprecipitation experiments, bivalent domains were also uncovered at endogenous PcG targets like the Hox genes.
Acknowledgements
Work of AA, MG and RP was supported by the ETH Zurich. MG is a member of the Life Science Zurich Graduate School (PhD Program in Molecular Life Sciences) and supported by a fellowship from the German Academic Scholarship Foundation.
Author contributions
AA conceived the project, collected samples, designed and performed experiments and wrote the manuscript. MG collected samples and provided critical feedback throughout the project. RP supervised the project. MG and RP provided critical feedback on the manuscript.
Disclosure statement
No potential conflict of interest was reported by the authors.
Supplemental material
Supplemental data for this article can be accessed here.
