Expression of Cyclin E or DP/E2F rescues the G1 arrest of trol mutant neuroblasts in the Drosophila larval central nervous system

The trol locus of Drosophila regulates the timing of neuroblast proliferation. In trol mutants, quiescent neuroblasts fail to begin division. We have investigated this cell cycle arrest to examine trol function. Induced expression of cyclin E or DP/E2F in trol mutants results in normal levels of dividing neuroblasts, while cyclin B expression has no effect. cyclin E expression is lower in the trol mutant larval CNS as assayed by quantitative RT-PCR, suggesting that trol neuroblasts are arrested in G1 due to lack of Cyclin E. Neither cyclin E nor E2F expression can phenocopy ana mutations, indicating that arrest caused by lack of Trol is different from Ana-mediated arrest.