Set1, Set2, and the Clock‐cycle complex are necessary to prevent age‐related retinal degeneration in Drosophila melanogaster

Abstract

Age‐related eye disease is a prevalent problem that is exacerbated by the rising, aging population. Drosophila melanogaster serves as a powerful model organism for studying age‐related eye disease, as they share 60% of their genetic material with humans. Here, we seek to understand how changes in gene expression regulate photoreceptor neuron survival during aging. A preliminary RNA interference screen was carried out to identify genes necessary for cell survival throughout aging. Microscopy imaging and reverse transcriptase quantitative polymerase chain reaction (RT‐qPCR) were used to further investigate the role of histone methyltransferases Set1 and Set2 and the transcription factor Clock in photoreceptor neuron survival. Set1 and Set2 add methyl groups to lysine residues of histone H3, while Clock forms a heterodimer with the transcription factor cycle to activate transcription of genes involved in the circadian rhythm. Microscopy imaging was used to qualitatively and quantitatively assess loss of rhabdomeres, compartments of photoreceptor cells responsible for phototransduction, in flies lacking expression of either Set1, Set2, or a functional Clock‐cycle complex. Flies expressing RNA interference against Set1 and Set2 show retinal degeneration at or before the age of 30 days. Flies that fail to form a functional Clock‐cycle complex due to expression of a dominant negative form of Clock (ClkDN) show progressive retinal degeneration starting at the age of 5 days. Interestingly, this retinal degeneration is rescued when flies are raised in the dark. These phenotypes were validated by measuring target gene expression using RT‐qPCR. RNA interference against mCherry and overexpression of LacZ were used as controls for Set1 and Set2 RNA interference and overexpression of ClkDN, respectively. These findings suggest that histone methylation and Clock‐dependent gene expression play a role in age‐related eye disease in both Drosophila and humans.