The Drosophila attP40 docking site and derivatives are insertion mutations of MSP300

Abstract

The {phi}C31 integrase system is widely used in Drosophila to allow transgene targeting to specific loci. Over the years, flies bearing any of more than 100 attP docking sites have been constructed. One popular docking site, termed attP40, is located close to the Nesprin-1 orthologue MSP300 and lies upstream of certain MSP300 isoforms and within the first intron of others. Here we show that attP40 causes larval muscle nuclear clustering, which is a phenotype also conferred by MSP300 mutations. We also show that flies bearing insertions within attP40 can exhibit decreased MSP300 transcript levels in third instar larvae. Finally, chromosomes carrying certain "transgenic RNAi project" (TRiP) insertions into attP40 can confer pupal or adult inviability, or infertility. These phenotypes do not require transcription from the insertions within attP40. These results demonstrate that attP40 and insertion derivatives act as MSP300 insertional mutations. These findings should be considered when interpreting data from attP40-bearing flies.