Drosophila gene probes

The ability to clone potentially important developmental genes by screening mouse libraries with Drosophila gene probes, together with the advent of in situ hybridization to study their spatial expression in embryos, provided the impetus for the explosion in mouse developmental studies over the last 15 years. 

Fly blood does not normally contain substances that kill bacteria, but flies inoculated with bacteria rapidly accumulate antibacterial proteins (ABs) in their blood. Wild type Drosophila have at least three different antibacterial proteins based on isoelectric points. Genetic variants identify structural genes for these antibacterial proteins. A DNA sequence that can encode a conserved portion of moth and fleshfly antibacterial proteins has been used to synthesize a complementary oligonucleotide probe. This probe recognizes a messenger RNA that appears in the fat body of Drosophila and Medflies only after they have been inoculated with bacteria. Bacteria-sensitive lethal mutations were induced to identify genes necessary for flies to survive a bacterial infection. 

To determine what cells make the immune-specific RNA we inoculated mid-third instar Drosophila larvae with bacteria and six hours later dissected them into fat bodies and fat body-free carcass. Total RNA was collected, separated by electrophoresis, transfered to nitrocellulose, and probed with labelled Pool 1 oligonucleotide. The results showed (Fig. 5) that intact inoculated larvae accumulate the immune-specific transcript while intact control larvae do not. The tissue dissection experiment showed that fat body cells of inoculated larvae contain transcripts homologous to the immune-specific probe, but the carcass does not. We conclude that fat body cells in Drosophila larvae accumulate a transcript that has homology to sarcotoxin when they have been inoculated with bacteria. We are currently cloning the responsible immune gene. 

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