Ectopic expression of BEAF32A in the Drosophila eye imaginal disc inhibitsdifferentiation of photoreceptor cells and induces apoptosis

Transgenic flies were established in which ectopic expression of boundary e lement-associated factor (BEAF) 32A was targeted to the Drosophila eye imag inal disc. The eyes of the adult fly displayed a severe rough eye phenotype . When these eyes were sectioned, most ommatidia were found to be fused and irregularly shaped rhabdomeres were observed. In the developing eye imagin al disc, expression of BEAF32A inhibited differentiation of photoreceptor c ells. Expression of BEAF32A also induced extensive apoptosis of eye imagina l disc cells and, consistent with this, co-expression of baculovirus P35 in the eye imaginal disc suppressed the BEAF32A-induced rough eye phenotype. To investigate the effects of BEAF32A on regulation of chromatin structure, genetic crosses of the BEAF32A-overexpressing flies with loss-of-function mutants for genes encoding other boundary element-binding factors or regula tors of chromatin structure were conducted. Interestingly, half-dose reduct ion of the su(Hiv) gene strongly enhanced the rough eye phenotype induced b y BEAF32A. Furthermore, genetic crosses of the transgenic flies with loss-o f-function mutants for genes interacting with Polycomb revealed specific li nks between BEAF32A and genes such as Distalless and kohtalo, suggesting a relation to the chromatin insulator function of BEAR In addition, genetic c rosses of transgenic flies expressing BEAF32A with a collection of Drosophi la deficiency stocks allowed us to identify several genomic regions, deleti ons of which caused enhancement or suppression of the BEAF32A-induced rough eye phenotype. The transgenic flies established in this study should be us eful to identify targets of BEAF32A and its positive or negative regulators in Drosophila.