Contrasting effects of aging on the expression of transposons, the piRNA machinery and mitochondrial transcripts in the Drosophila ovary.

Abstract

Redistribution of heterochromatin during aging has been linked to the de-repression of transposable elements and an overall loss of gene regulation in the soma. Whether or not epigenetic factors such as heterochromatin marks are perturbed in reproductive and germline tissues is of particular interest because some epigenetic factors are known to transmit across generations. Additionally, the relative contribution of factors intrinsic or extrinsic to the germ line have in reproductive decline remains unknown. Using mRNA sequencing data from late stage egg chambers in Drosophila melanogaster, we show that age-related expression changes occur in genes residing in heterochromatin, particularly on the largely heterochromatic 4th chromosome. In addition, we identify an increase in expression of the piRNA machinery. We further identify a striking age-related reduction in mitochondrial transcripts that we can attribute to the somatic tissues. Other than a modest increase in overall TE expression in the aging germline, we find no global TE de-repression in reproductive tissues. Rather, the observed effects of aging on TEs are primarily strain and family specific. These results indicate unique responses in somatic versus germline tissue with regards to epigenetic aging effects and suggest that the global loss of TE control observed in other studies may be specific to certain tissues, genetic backgrounds and TE family. This study also demonstrates that while age-related effects can be maternally transmitted, the germline is generally robust to age-related changes.