P-ELEMENT INSERTS IN TRANSGENIC FLIES - A CAUTIONARY TALE

The fruitfly, Drosophila melanogaster, can be transfected with P-eleme nts and induced to overexpress a transfected gene whose impact on life span can be measured. Here, it is reported that in previous experiment s a transfected gene was not expressed. This suggested a new statistic al analysis indicating that (1) the size of the insert, the position a nd the interactions of the insert with the genetic backgrounds into wh ich the P-element are inserted have effects on lifespan similar to tho se attributed to overexpression; (2) these effects occur without expre ssion of the transfected gene; and (3) effects of interactions with ba ckgrounds and effects of interactions with backgrounds and effects of positions are as large as responses to six generations of strong direc tional artificial selection. Reports of effects of overexpression of t ransfected genes on lifespan in Drosophila melanogaster may be experim ental artefacts. Credible experiments on the phenotypic effects of tra nsgenesis need proper controls for the effects of insert size and posi tion and should estimate the magnitudes of interactions of treatment w ith genetic backgrounds.