One of a major function of programmed cell death (apoptosis) is the removal of cells
which suffered oncogenic mutations, thereby preventing cancerous transformation. By
making use of a Double-Headed-EP (DEP) transposon, a P element derivative made in
our laboratory, we made an insertional mutagenesis screen in Drosophila melanogaster
to identify genes which, when overexpressed, suppress the p53-activated apoptosis.
The DEP element has Gal4-activatable, outward-directed UAS-promoters at both ends
which can be deleted separately in vivo. In the DEP insertion mutants, we used the
GMR-Gal4 driver to induce transcription from both UAS-promoters and tested the suppression
effect on the apoptotic rough eye phenotype generated by an activated UAS-p53 transgene.
By DEP insertions, seven genes were identified which suppressed the p53-induced apoptosis.
In four mutants, the suppression effect resulted from single genes activated by one
UAS-promoter (Pka-R2, Rga, crol, Spt5). In the other three (Orct2, Polr2M, stg), deleting
either UAS-promoter eliminated the suppression effect. In qPCR experiments we found
that the genes in the vicinity of the DEP insertion also showed an elevated expression
level. This suggested an additive effect of the nearby genes on suppressing apoptosis.
In the eucaryotic genomes there are co-expressed gene clusters. Three of the DEP insertion
mutants are included and two are in close vicinity of separate co-expressed gene clusters.
This raises the possibility that the activity of some of the genes in these clusters
may help the suppression of the apoptotic cell death.
