The recently accepted phenomenon of adult neurogenesis is important for basic biological research and, potentially, can have major implications for the treatment of age-related cognitive decline and disease. Investigation into the mechanisms of adult neurogenesis and its ability to replenish brain circuits with new functional neurons requires whole animal models.  Zebrafish, a diurnal vertebrate, has robust cell proliferation in several neurogenic niches, including the cerebellum and dorsal telencephalon, the latter bearing homology to mammalian hippocampus. Because zebrafish demonstrate rapid regeneration in all tissues, including successful repair following brain traumas, they are promising as a model for designing therapies for human brain traumas or stroke. Their long lifespan and gradual aging also makes them an interesting model for the role of neurogenesis in counteracting human neurodegenerative disorders of aging. In different models, it has been found that cell proliferation in adult brain can be significantly affected by behavioral and environmental factors. Among those is nutrition, impacting adult neurogenesis through the amount of caloric intake, meal frequency, and meal content. The study presented here addressed the effects of nutritional factors on adult neurogenesis in a zebrafish model of premature aging due to excessive caloric food intake since early development. Fish were exposed to fasting, different diets and feeding schedules, with the rate of cell proliferation documented in two largest neurogenic niches of the zebrafish brain, the cerebellum and dorsal telencephalon. Here we show that, under normal conditions, fish with premature aging demonstrate dramatic decline in adult neurogenesis in both niches, when compared to age-matched control. The present findings establish an effect of nutrition on neurogenesis in the cerebellum and dorsal telencephalon of adult zebrafish. Zebrafish maintained on HFD, subjected to fasting, or fed only in the evenings showed significant changes in neurogenesis in two distinct neurogenic niches from that of control fish. Remarkably, the two brain regions under investigation displayed partially different responses to nutrition related factors. This was reflected in the cerebellar niche in which neurogenesis was significantly increased by 24h fast/24h refeed, high fat diet, and evening feeding conditions.  Neurogenesis of the cerebellum was significantly decreased in 24h fast, 42h fast/refeed conditions.  In the dorsal telencephalon, neurogenesis was significantly amplified by high protein, and similar to the cerebellum, high fat diet and evening feeding conditions.  In contrast, neurogenesis of the dorsal telencephalon was significantly attenuated only in the 72h fasting condition. This study provides evidence that nutrition plays important role in the modulation of adult neurogenesis in zebrafish, and presence of niche-specific responses to nutritional factors. This further suggests that zebrafish can serve as a model for studying the effects of specific diets, metabolic factors and drugs that affect metabolism in search for prophylactic and therapeutic measures for age-related cognitive decline or neurodegenerative disorders.

We previously described BT2, a BTB/POZ domain containing protein, as an activator of telomerase in Arabidopsis thaliana. In the current study, I present evidence of its interesting roles in mediating multiple hormone, stress and metabolic responses in plants. Steady-state expression of BT2 mRNA was regulated diurnally and was under the control of circadian clock, with a maximum expression in the dark. BT2 mRNA was responsive to nutrient status and to multiple biotic and abiotic stress signals. Using bt2 loss-of-function and BT2 over-expressing lines, I show that BT2 suppresses sugar and ABA-mediated responses during germination. BT2 is also essential for transcriptional gene activation mediated by CaMV 35S enhancers in Arabidopsis. Loss of BT2 in several well-characterized 35S enhancer activation-tagged lines such as yucca1d, pap1d, jaw1d etc., resulted in suppression of the activation phenotypes. The suppression of the phenotypes was due to decreased transcription of the activation-tagged genes. I further demonstrate that BT2 genetically interacts with CULLIN3. I propose that BT2 and CULLIN3 are components of a ubiquitin ligase complex. Together with associated proteins BET9 and BET10, the BT2 complex is required for CaMV 35S enhancer-mediated activation of gene expression and may regulate expression of target genes involved in multiple responses to fluctuating biotic and abiotic conditions. I also found that BT2 protein levels are tightly regulated in plants. BT2 protein was primarily localized in the nucleus and was developmentally regulated. BT2 turn-over was regulated in part by the 26S-proteosome, and rare codons present in its open reading frame affected BT2 protein accumulation. In addition to BT2, its orthologs, BT1, BT3, BT4 and BT5, also responded to light, clock and nutrients, with some differences. Moreover, BT1, BT3 and BT4 were also required for 35S enhancer-mediated activation of gene expression. I propose that BT family proteins assemble into multi-protein complexes to mediate multiple responses to changing environmental and nutritional conditions.

This research explores the capacity for functional photoreception in larvae of the mountain pine beetle (Dendroctonus ponderosae), an extremely important forest pest insect that is well adapted for development beneath the bark of pine trees. Phototaxis tests, gene expression analysis and development experiments were integrated to assess mountain pine beetle larvae for light sensitivity. When presented with a phototaxis choice test, larvae preferred dark over light microhabitats, revealing that larvae sense and respond behaviourally to light. Long wavelength opsin transcription was identified in all life stages, including eggs and larvae, suggesting that D. ponderosae possesses extraretinal photosensitive capabilities across its life cycle. The long wavelength opsin could function in phototaxis or the development phenology of immature beetles, while the ultraviolet opsin, only found to be expressed in pupae and adults, is likely to function in dispersal via the compound eyes. Results from two development experiments reveal an effect of photoperiod treatment on beetle development rate when reared from the egg stage, but not when reared from mature larvae, indicating that a critical photosensitive life stage(s) must occur in D. ponderosae prior to the third larval instar. An effect of photoperiod on adult emergence rates, however, appears to be independent of larval rearing conditions. The discovery of opsin expression and negative phototaxis in eyeless mountain pine beetle larvae, in addition to an effect of photoperiod on immature development and adult emergence rates, suggest that light and photoperiodism likely function in survival and life cycle coordination in this species. / Graduate / 2018-10-17