Epigenetic regulation of extreme longevity differences in ant castes

摘要

ABSTRACT Ants exhibit highly evolved eusocial behaviors including stark division of labor among female castes, where the queen carries out all reproduction and worker castes forage for food and defend the colony. Interestingly, and of great relevance to aging research, the sterile workers are short-lived, while the reproductive queens are long-lived, with lifespans differing three to ten-fold between queen and worker. Remarkably, the genomes of these sterile and reproductive castes are nearly identical, and thus differences in lifespan (LS) and behavior likely result from epigenetic regulation. Furthermore, in the species Harpegnathos saltator, loss or removal of the queen leads to altered behavior in the workers, with antennal dueling and eventual ascendance of typically one or two workers into reproductive “gamergate”, or pseudo-queen. From a longevity perspective, the gamergate exhibits longer LS and thus it appears that both behavior and lifespan are epigenetically determined during this switch. In addition, older workers reprogram much less efficiently into reproductive gamergate status. Our overall premise is that epigenetic regulation is at the heart of this caste-differentiated life span disparity, and that once we understand the basis of the epigenetic regulation, we can manipulate lifespan with epigenetic therapeutics and genetics in this relatively simple but socially complex organism. These results will provide fundamental knowledge that can be investigated in more sophisticated mammals. We propose to utilize H. saltator ants to investigate the epigenetic and physiological basis of the dramatic LS differences between reproductive and worker castes. We will carry out transcriptomic, proteomic, and epigenomic profiling of workers and queens of the same chronological age, and of young and old queens, to explore the basis of the plasticity in lifespan. We hypothesize that both known and novel mechanisms are lengthening LS in queens, which show such dramatic difference from worker LS. In addition, we will uncover the basis of the inefficient reprogramming of older workers into reproductive gamergates. Our recent published evidence (Science, 2016) supports the view that behavioral plasticity in ants is enhanced by epigenetic mechanisms during young adulthood, and that this plasticity is lost with age; however, the molecular mechanisms underlying this phenomenon remain unknown. Our preliminary data regarding chromatin marking show that regulatory loci near to active genes in gamergate queens bear activating histone H3K27 acetylation and these same loci in worker are marked with repressive H3K27 methylation. Intriguingly, these repressed loci in worker ants appear to be “poised” for activation with H4K16 acetylation. We hypothesize that in young workers key loci are epigenetically poised to become activated and this poising becomes degraded as workers age, leading to inefficient reprogramming to reproductive status. In the proposed research we will test this proposal using epigenetic therapeutics and genetics. The ant model system provides an exceptional opportunity to integrate social behavior with aging, and to uncover key epigenetic processes underlying universal aging pathways.