Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Biology

First Advisor

Shelley L. Berger

Abstract

Eusocial insect colonies divide behaviors among specialist groups called castes. In some species, caste identity is determined by the interaction of endogenous (e.g. genomic) and exogenous (e.g. juvenile hormone from nurses) during larval development, suggesting epigenetic mechanisms underlie plastic traits tied to caste identity. Previous work has linked histone H3 lysine 27 acetylation (H3K27ac) and morphological caste in Major and Minor workers of the ant Camponotus floridanus, and we hypothesized caste-specific behaviors, such as foraging, may be similarly regulated by histone acetylation. To test this hypothesis, we fed mature (~30d old) Majors and Minors with histone deacetylase inhibitors (HDACi), and CBP-dependent histone acetyl transferase inhibitors (HATi). We observed foraging enhancement after HDACi, and foraging suppression after HATi in Minors. Curiously, we did not observe increased foraging in mature (~30d) Majors. However, HDACi injections in callow (0-1d old) Majors succeeded in causing stable reprogramming of foraging behavior, indicating a critical period, or ‘window’ of epigenetic sensitivity to HDACi exists in young majors. To address this possibility, we injected Majors with HDACi in a time course and observed juvenile (d0-d5) Majors are susceptible to reprogramming, whereas mature (d10) Majors are not. To assess innate differences in the brain between castes we conducted an RNA-seq screen in untreated Major and Minor workers 0, 5, and 10 days old, and detected caste-specific patterns of juvenile hormone and ecdysone signaling. Finally, to understand the transcriptional and epigenetic dynamics of reprogramming, we conducted RNA-seq and ChIP-seq in HDACi treated Major brains, and detected consistent upregulation of members of the neuron restrictive silencing factor (NRSF/REST) repressive complex (e.g. CoREST, RPD3, ttk). Notably, the top downregulated gene after HDACi is juvenile hormone esterase (JHe), which antagonizes JH signaling and inhibits foraging behavior in many eusocial insects. Thus, our results suggest REST/CoREST-mediated repression of JHe may be a significant source of stable changes to foraging in behaviorally reprogrammed Majors.

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