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Overexpression of Drosophila RFX3 Induces Apoptosis and Interferes with Differentiation of Photoreceptor Cells

Toshimi Sugimoto, Takako Ueda, Hideki Yoshida, Akira Murakami and Masamitsu Yamaguchi

Regulatory Factor X (RFX) is a protein containing a characteristic DNA binding domain that is called RFX domain. Members of the RFX family are known to be present in human, mouse, Drosophila, Caenorhabditis elegans, Schizosaccharomyces pombe and Saccharomyces cerevisiae. Two RFX proteins, Drosophila RFX (dRFX) and dRFX2 have been identified in Drosophila so far. It is known that dRFX is involved in the differentiation of central and peripheral nerves, while dRFX2 is essential to the cell cycle progression and it may be involved in regulation of apoptosis. A novel protein, dRFX3 carrying RFX domain was identified by a Drosophila genome database search. dRFX3 is a likely homolog to the human RFX5, because of a significant sequence similarity in RFX domains between these two proteins. Two lines of transgenic fly carrying the HA-dRFX3 cDNA were established. Adult flies expressing dRFX3 specifically in the eye and the wing imaginal discs exhibited severe rough eye and atrophied wing phenotypes, respectively. 5-Bromo-2’-deoxyuridine incorporation assays and the immunological detection using anti-Cyclin B antibody indicated that the overexpression of dRFX3 in the eye imaginal discs exerted no effect on the cell cycle progressions. On the other hand, overexpression of dRFX3 in the eye imaginal discs interfered with the differentiation of R2/R5 photoreceptor cells and also induced apoptosis. These data suggest that the dRFX3 plays a negative role for the differentiation of R2/R5 photoreceptor cells and plays a positive role in the regulation of apoptosis.