The Levels of the bancal Product, a Drosophila Homologue of Vertebrate hnRNP K Protein, Affect Cell Proliferation and Apoptosis in Imaginal Disc Cells

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Abstract
We have characterized the Drosophila bancal gene, which encodes a Drosophila homologue of the vertebrate hnRNP K protein. The bancal gene is essential for the correct size of adult appendages. Reduction of appendage size in bancalmutant flies appears to be due mainly to a reduction in the number of cell divisions in the imaginal discs. Transgenes expressingDrosophila or human hnRNP K are able to rescue weakbancal phenotype, showing the functional similarity of these proteins in vivo. High levels of either human orDrosophila hnRNP K protein in imaginal discs induces programmed cell death. Expression of the antiapoptotic P35 protein suppresses this phenotype in the eye, suggesting that apoptosis is the major cellular defect caused by overexpression of K protein. Finally, the human K protein acts as a negative regulator of bancalgene expression. We propose that negative autoregulation limits the level of Bancal protein produced in vivo.