This antagonistic relationship is conserved in flies, where homeotic transformations caused by PcG mutations can be suppressed by compensating trithorax mutations (Tamkun et al., 1992; Elfring et al., 1994; Kennison and Tamkun, 1988). However, the interaction seems more complex in mammals: importantly, BAF synergizes with Polycomb at all four Hox loci in ES cells to prevent precocious differentiation (Ho et al., 2011). Nevertheless, one of the key functions of esBAF is to maintain the accessibility of actively transcribed genes by preventing the formation of Polycomb repressive domains in the ES cell genome.
