Antagonistic activities of PcG and TrxG complexes in facultative heterochromatin

(a) Activator proteins recruit the TrxG complex to the chromatin, resulting in erasing of repressive histone marks and writing of positive histone marks. HAT complexes are also often recruited to add positive acetyl marks. Conversely, repressor proteins recruit the PcG complex to the chromatin, resulting in erasing of positive histone marks and writing of repressive histone marks. HDAC complexes are also often recruited to erase positive acetyl marks. (b) Ubx expression (blue) is activated and maintained posteriorly in wild-type Drosophila, but its repression is lost in PcG mutants and its maintenance is lost in TrxG mutants(a) Activator proteins recruit the TrxG complex to the chromatin, resulting in erasing of repressive histone marks and writing of positive histone marks. HAT complexes are also often recruited to add positive acetyl marks. Conversely, repressor proteins recruit the PcG complex to the chromatin, resulting in erasing of positive histone marks and writing of repressive histone marks. HDAC complexes are also often recruited to erase positive acetyl marks. (b) Ubx expression (blue) is activated and maintained posteriorly in wild-type Drosophila, but its repression is lost in PcG mutants and its maintenance is lost in TrxG mutants

(a) Trithorax group (TrxG) complex: H3K4 methylase activity H3K3me3 reader Mono-, di—, and tri— H3K27 demethylase o Activator recruits , Activators also recruit: TrxG complex 8 HATs—histone acetylas¢\ o Transcription activated Activator [—H3K4me3—I RNA pol u Mica ic rc m'i'iN‘A 5' Polycomb group (PcG) complex: The opening Up 9f Chromatin H3K27 methyiase activity into a euchromatic state Via the H3K27me3 reader action of activators recruiting Mono-, di-, and tri-H3K4 demethylase the TrxG complex allows RNA pol || binding and transcrlption Repressors also recruit: a Repressor in initiation. HDACs—histone deacetylases recrurts PCG complex - y : o o The condensing of dwromatin into a w .y ;_. t, ; Z 3 facuhative heterodwromatic state via the '96 action of repressors recruiting the PCG complex forms a repressed chromatin state keeping gene expression off. (b) Early embryo Later embryo l l Polycombgroup Glflllll) - (PcG) mutant l l Trithorax (TrxG) mutant dull") @ l l