Doctoral Dissertation Research: Investigating Genomic and Expression-level Adaptations for Detoxification in Primates

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Cyanide is a poison that is common among plants and toxic to most animals. Nonetheless, three species of bamboo lemur focus most of their feeding time on various parts of Malagasy giant bamboo, which exposes the lemurs to 12-50 times their estimated lethal dose of cyanide on a daily basis. This project will examine the underlying physiology and genomics of cyanide detoxification in bamboo lemurs. In addition to addressing the decades-old puzzle of how these lemurs are able to consume high levels of cyanide, this study may inform the development of therapies, antidotes, or prophylactics to cyanide exposure in humans. During the course of this work, the PI and co-PI will invite and recruit undergraduates from Kent State University's McNair Scholars Program, whose mission is to help first-generation, low-income undergraduates matriculate to a doctoral degree program. The co-PI will also utilize close ties with Northeast Ohio's public libraries and schools to present this project to students and the general public.The central questions of this study focus on known routes of cyanide detoxification among mammals. Low doses of the poison can be metabolized by a variety of conserved mechanisms, foremost among which is a pathway that uses sulfurtransferase enzymes. The limiting factors for this mechanism appear to be relative expression levels for these enzymes and the availability of sulfur-donor molecules (e.g., thiosulfate). Therefore, the first working hypothesis of this study is that H. aureus has adapted to detoxify its highly cyanogenic diet through positive selection on genes involved in the metabolism of sulfur or sulfur-containing amino acids. This hypothesis will be tested by assembling and mining a reference-quality genome for H. aureus and comparing it to data taken from a proposed genome assembly for Lemur catta, the most closely related species of dietary generalist. It is further hypothesized that H. aureus detoxifies its high levels of circulating cyanide through adaptive changes to the composition of the bloodstream. This second hypothesis will be tested by transcriptomic and metabolomic methods in order to compare the expression profiles and thiosulfate levels, respectively, of free-ranging H. aureus and captive L. catta. Together, these methods will examine adaptive changes in the H. aureus genome, as well as the whole-blood transcriptome and metabolome, which are related to the exceptional cyanide tolerance of this species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.