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GAL4 causes developmental defects and apoptosis when expressed in the developing eye of Drosophila melanogaster
Jamie M. Kramer and Brian E. Staveley
Department of Biology, Memorial University of Newfoundland, St. John’s,
Newfoundland, Canada A1B 3X9
Corresponding author: B.E. Staveley
Genet. Mol. Res. 2 (1): 43-47 (2003)
Received December 13, 2002
Published March 10, 2003

ABSTRACT. The UAS/GAL4 ectopic expression system is widely used in Drosophila melanogaster for the overexpression of transgenes. This system operates under the assumption that the yeast transcription factor, GAL4, is inactive in D. melanogaster. Thus, GAL4 can be expressed under the control of D. melanogaster-specific promoters with little effect upon the organism. We have shown that expression of GAL4 in the developing eye under the control of the glass multiple reporter (GMR) promoter element does have an effect on eye development. Although GMR-GAL4 heterozygotes appear normal when raised at 25°C, the homozygotes have a highly disorganized ommatidial array. In addition, the levels of apoptosis in the third-instar larval eye imaginal disc (where GAL4 is expressed) are slightly higher in GMR-GAL4 heterozygotes, and much higher in GMR-GAL4 homozygotes when compared to wild type discs. The morphological eye defects caused by GMR-GAL4 are significantly enhanced when flies are raised at 29°C (presumably due to the higher activity of GAL4 at this temperature); however, the levels of apoptosis appear to be similar at these two temperatures. Taken together, these data suggest that GAL4 can have adverse effects on D. melanogaster development, especially at high expression levels. In addition, GAL4 appears to induce apoptosis even in the absence of any visible morphological defects. Thus, despite the benefits of the UAS/GAL4 ectopic expression system, one must use caution in the design and interpretation of experiments.

Key words: Drosophila melanogaster, Eye development, Apoptosis, UAS/GAL4 ectopic expression system



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