Involvement of winged eye encoding a chromatin-associated bromo-adjacent homology domain protein in disc specification

How organ identity is determined is a fundamental question in developmental biology. InDrosophila , field-specific selector genes, such aseyeless (ey ) for eyes andvestigial (vg ) for wings, participate in the determination of imaginal disc-specific identity. We performed gain-of-function screening and identified a gene namedwinged eye (wge ), which encodes a bromo-adjacent homology domain protein that localizes at specific sites on chromosomes in a bromo-adjacent homology domain-dependent manner. Overexpression ofwge -induced ectopic wings with antero-posterior and dorso-ventral axes in the eye field in a region-specific Hox gene-(Antennapedia ) independent manner. Overexpression ofwge was sufficient for ectopic expression ofvg in eye discs. A context-dependent requirement ofwge was demonstrated forvg expression in wing discs and for expression ofeyes absent (eya ), a control gene for eye development downstream ofey , in eye discs. In contrast tovg , however, overexpression ofwge inhibited EY-mediated expression ofeya . Consistent with colocalization on polytene chromosomes of WGE and Posterior sex combs (PSC), a Polycomb group gene product, we demonstrated an antagonistic genetic interaction betweenwge andPsc . These findings suggest thatwge functions in the determination of disc-specific identity, downstream of Hox genes.