RNA-seq to determine PRC2 targets in the aging Drosophila brain.

Aging is a prominent risk factor for neurodegenerative disease, therefore defining mechanisms critical for healthy brain aging should lead to insight into genes that modulate susceptibility to disease. To define such genes, we have pursued analysis of miR-34 mutants in Drosophila. The miR-34 mutant brain displays a gene profile of accelerated aging, and miR-34 upregulation is a potent suppressor of polyglutamine-induced neurodegeneration. We investigated targets of miR-34 to define those important for its functions in mitigating degeneration and impacting health of the brain with age. These studies show that miR-34 targets for silencing two components of polycomb repressive complex 2 (PRC2)—Pcl and Su(z)12—in the brain with age. PRC2 is a histone methyltransferase that confers the repressive H3K27me3 mark, suggesting that a critical role of miR-34 is to modulate the function of PRC2 to silence key genes in the brain with age. Remarkably, gene expression profiling of the brains of hypomorphic mutants in Enhancer of zeste (E(z)), the enzymatic methyltransferase component of PRC2, revealed a younger brain transcriptome profile and identified the small heat shock proteins as key modulated genes. These findings indicate that PRC2 epigenetic mechanisms impact the susceptibility of the brain to degenerative disease with age, and highlight the role of small heat shock proteins to protect the brain from age-associated decline and disease. The design involves three factors: genotype, age, and cultivation temperature. Genotype can be either w[1118] (wild-type control) or w[1118]; E(z)[61] / E(z)[731] (E(z) hypomorphic mutant). Samples have an age of either 3d (3 days) or 20d (20 days). Animals are cultivated at either 25 degrees Celsius or 29 degrees Celsius. Samples are derived from Drosophila brain. We evaluate changes in gene expression with age. We also evaluate changes in gene expression in animals with hypomorphic mutations in E(z), with blocking on temperature.