Sleep is required to consolidate odor memory and remodel olfactory synapses

Animals with complex nervous systems demand sleep for memory consolidation and synaptic remodeling. Here, we show that, although the Caenorhabditis elegans nervous system has a limited number of neurons, sleep is necessary for both processes. In addition, it is unclear if, in any system, sleep collaborates with experience to alter synapses between specific neurons and whether this ultimately affects behavior. C. elegans neurons have defined connections and well-described contributions to behavior. We show that spaced odor-training and post-training sleep induce long-term memory. Memory consolidation, but not acquisition, requires a pair of interneurons, the AIYs, which play a role in odor-seeking behavior. In worms that consolidate memory, both sleep and odor conditioning are required to diminish inhibitory synaptic connections between the AWC chemosensory neurons and the AIYs. Thus, we demonstrate in a living organism that sleep is required for events immediately after training that drive memory consolidation and alter synaptic structures

Noncanonical roles for RNA in maintaining genomic stability and influencing organismal physiology

It is becoming increasingly clear that sensory neurons are able to integrate information about environmental changes to regulate aspects of an organism’s physiology. The L’Etoile lab has gathered evidence suggesting that mobile small RNAs may represent a previously unidentified endocrine signal and thus, might regulate various physiological outputs. My thesis work used different models and experimental approaches to test the hypothesis that small RNA machinery acts as a regulator of mitotic signals to ensure genomic integrity in proliferative cell populations. The proliferative germ cells (PGCs) in the C. elegans nematode and MCF10As, a human derived, non-tumorgenic breast epithelial cell line, are complementary models that are ideal to study how the small RNA pathway might regulate mitosis.I discovered that loss of NRDE2, a nuclear RNAi-dependent protein, induces DNA damage accumulation specifically under conditions of stress, such as high cultivation temperature in C. elegans or Aurora B Kinase oncogenic overexpression in MCF10A cells. I found that NRDE2 interacts with β-actin in unstressed mammalian cells. This interaction is dramatically reduced upon DNA damage and increased in the absence of RNA. I propose a model by which NRDE2 associates with actin only when DNA is intact and the bulk of nuclear actin is monomeric. Thus, NRDE2 may dissociate from actin when it becomes filamentous as a result of DNA damage. This implies that, NRDE2, in its role as a heterochromatin factor, binds to monomeric actin, protecting the genome from DNA damage in stressful conditions.I have also gathered preliminary data showing that the AWC olfactory sensory neurons are required to regulate brood size and egg laying pattern in C. elegans. Furthermore, my preliminary evidence indicates that SID-1, an import channel required for RNAi spreading, is required to regulate brood size and germ cell proliferation. This suggests that mobile RNAs could act as hormones to allow for gene specific regulation of distant target cells, providing a novel pathway for scientists to understand regulation of cell-cell communication and the subsequent consequences of its dysfunction.This thesis work lays groundwork for further studies into small RNAs as regulators for epigenetic inheritance, cancer, reproduction and mental health

Expression of an expanded CGG-repeat RNA in a single pair of primary sensory neurons impairs olfactory adaptation in Caenorhabditis elegans.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a severe neurodegenerative disorder that affects carriers of premutation CGG-repeat expansion alleles of the fragile X mental retardation 1 (FMR1) gene; current evidence supports a causal role of the expanded CGG repeat within the FMR1 mRNA in the pathogenesis of FXTAS. Though the mRNA has been observed to induce cellular toxicity in FXTAS, the mechanisms are unclear. One common neurophysiological characteristic of FXTAS patients is their inability to properly attenuate their response to an auditory stimulus upon receipt of a small pre-stimulus. Therefore, to gain genetic and cell biological insight into FXTAS, we examined the effect of expanded CGG repeats on the plasticity of the olfactory response of the genetically tractable nematode, Caenorhabditis elegans (C. elegans). While C. elegans is innately attracted to odors, this response can be downregulated if the odor is paired with starvation. We found that expressing expanded CGG repeats in olfactory neurons interfered with this plasticity without affecting either the innate odor-seeking response or the olfactory neuronal morphology. Interrogation of three RNA regulatory pathways indicated that the expanded CGG repeats act via the C. elegans microRNA (miRNA)-specific Argonaute ALG-2 to diminish olfactory plasticity. This observation suggests that the miRNA-Argonaute pathway may play a pathogenic role in subverting neuronal function in FXTAS

Expression of an expanded CGG-repeat RNA in a single pair of primary sensory neurons impairs olfactory adaptation in Caenorhabditis elegans.

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a severe neurodegenerative disorder that affects carriers of premutation CGG-repeat expansion alleles of the fragile X mental retardation 1 (FMR1) gene; current evidence supports a causal role of the expanded CGG repeat within the FMR1 mRNA in the pathogenesis of FXTAS. Though the mRNA has been observed to induce cellular toxicity in FXTAS, the mechanisms are unclear. One common neurophysiological characteristic of FXTAS patients is their inability to properly attenuate their response to an auditory stimulus upon receipt of a small pre-stimulus. Therefore, to gain genetic and cell biological insight into FXTAS, we examined the effect of expanded CGG repeats on the plasticity of the olfactory response of the genetically tractable nematode, Caenorhabditis elegans (C. elegans). While C. elegans is innately attracted to odors, this response can be downregulated if the odor is paired with starvation. We found that expressing expanded CGG repeats in olfactory neurons interfered with this plasticity without affecting either the innate odor-seeking response or the olfactory neuronal morphology. Interrogation of three RNA regulatory pathways indicated that the expanded CGG repeats act via the C. elegans microRNA (miRNA)-specific Argonaute ALG-2 to diminish olfactory plasticity. This observation suggests that the miRNA-Argonaute pathway may play a pathogenic role in subverting neuronal function in FXTAS

Expression of an expanded CGG-repeat RNA in a single pair of primary sensory neurons impairs olfactory adaptation in Caenorhabditis elegans

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a severe neurodegenerative disorder that affects carriers of premutation CGG-repeat expansion alleles of the fragile X mental retardation 1 (FMR1) gene; current evidence supports a causal role of the expanded CGG repeat within the FMR1 mRNA in the pathogenesis of FXTAS. Though the mRNA has been observed to induce cellular toxicity in FXTAS, the mechanisms are unclear. One common neurophysiological characteristic of FXTAS patients is their inability to properly attenuate their response to an auditory stimulus upon receipt of a small pre-stimulus. Therefore, to gain genetic and cell biological insight into FXTAS, we examined the effect of expanded CGG repeats on the plasticity of the olfactory response of the genetically tractable nematode, Caenorhabditis elegans (C. elegans). While C. elegans is innately attracted to odors, this response can be downregulated if the odor is paired with starvation. We found that expressing expanded CGG repeats in olfactory neurons interfered with this plasticity without affecting either the innate odor-seeking response or the olfactory neuronal morphology. Interrogation of three RNA regulatory pathways indicated that the expanded CGG repeats act via the C. elegans microRNA (miRNA)-specific Argonaute ALG-2 to diminish olfactory plasticity. This observation suggests that the miRNA-Argonaute pathway may play a pathogenic role in subverting neuronal function in FXTAS