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Open Access Publications from the University of California

Scholarly Works (5 results)

  • Thesis
  • Peer Reviewed
UC San Francisco Electronic Theses and Dissertations (2010)

Regulation of nutrient consumption and storage is a complex process requiring numerous interconnected genetic pathways that monitor and respond to both environmental and internal conditions. Though we have a good framework understanding of some of the basic modules of this network, our grasp of the intricate regulation of these processes remains limited.

We have utilized the model organism C. elegans to investigate the genetic pathways regulating nutrient storage. To monitor nutritional status of these animals, we have utilized a number of previously described assays, and have adapted and improved others, described in chapter II. By visually monitoring aspects of nutrient storage, while simultaneously manipulating genes, either individually or in combinations, we have described a novel pathway regulating lipid storage, described in chapter III, and have begun work on a second pathway which appears to regulate the cell biology of a nutrient storage compartment, described in chapter IV.

In a forward genetic screen for genes regulating lipid storage, we isolated a mutation in acs-3, encoding a long chain fatty acyl-CoA synthase. These mutants exhibit elevated lipid staining intensity, and abnormally large intestinal lipid droplets. Our characterization of this gene revealed that it is expressed in a limited set of tissues, and expression of acs-3 in the hypodermal seam cells, a stem cell-like population, is sufficient to rescue the abnormal lipid storage of mutant animals. We performed both unbiased and candidate suppressor screens, and identified a set of genes that function in the acs-3 pathway to regulate nutrient storage. Our findings suggest a pathway in which acs-3, acdh-10, acdh-11 and elo-6 function to modulate fatty acyl-CoA levels, which in turn regulate nhr-25 function, perhaps as components of nhr-25 ligands.

The work described here sheds light on networks of genes that likely function in different tissues to regulate nutrient storage in a concerted fashion. In addition, these findings underscore the utility of genetic interrogation of metabolic networks, and demonstrate that enzymes with well-understood enzymatic activities can function in unexpected ensembles to modulated metabolism via unpredictable mechanisms.

    Cover page: Genetic Analysis of C. elegans Metabolism
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2016)
    Hunger and thirst are ancient homeostatic drives for food and water consumption. Although molecular and neural mechanisms underlying these drives are currently being uncovered, less is known about how hunger and thirst interact. Here, we use molecular genetic, behavioral, and anatomical studies in Drosophila to identify four neurons that modulate food and water consumption. Activation of these neurons promotes sugar consumption and restricts water consumption, whereas inactivation promotes water consumption and restricts sugar consumption. By calcium imaging studies, we show that these neurons are directly regulated by a hormone signal of nutrient levels and by osmolality. Finally, we identify a hormone receptor and an osmolality-sensitive ion channel that underlie this regulation. Thus, a small population of neurons senses internal signals of nutrient and water availability to balance sugar and water consumption. Our results suggest an elegant mechanism by which interoceptive neurons oppositely regulate homeostatic drives to eat and drink.
      Cover page: Coupled Sensing of Hunger and Thirst Signals Balances Sugar and Water Consumption
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2015)
      Gustatory receptors and peripheral taste cells have been identified in flies and mammals, revealing that sensory cells are tuned to taste modality across species. How taste modalities are processed in higher brain centers to guide feeding decisions is unresolved. Here, we developed a large-scale calcium-imaging approach coupled with cell labeling to examine how different taste modalities are processed in the fly brain. These studies reveal that sweet, bitter, and water sensory cells activate different cell populations throughout the subesophageal zone, with most cells responding to a single taste modality. Pathways for sweet and bitter tastes are segregated from sensory input to motor output, and this segregation is maintained in higher brain areas, including regions implicated in learning and neuromodulation. Our work reveals independent processing of appetitive and aversive tastes, suggesting that flies and mammals use a similar coding strategy to ensure innate responses to salient compounds.
        Cover page: Representations of Taste Modality in the Drosophila Brain
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2014)
        Metazoan transcription factors control distinct networks of genes in specific tissues, yet understanding how these networks are integrated into physiology, development, and homeostasis remains challenging. Inactivation of the nuclear hormone receptor nhr-25 ameliorates developmental and metabolic phenotypes associated with loss of function of an acyl-CoA synthetase gene, acs-3. ACS-3 activity prevents aberrantly high NHR-25 activity. Here, we investigated this relationship further by examining gene expression patterns following acs-3 and nhr-25 inactivation. Unexpectedly, we found that the acs-3 mutation or nhr-25 RNAi resulted in similar transcriptomes with enrichment in innate immunity and stress response gene expression. Mutants of either gene exhibited distinct sensitivities to pathogens and environmental stresses. Only nhr-25 was required for wild-type levels of resistance to the bacterial pathogen P. aeruginosa and only acs-3 was required for wild-type levels of resistance to osmotic stress and the oxidative stress generator, juglone. Inactivation of either acs-3 or nhr-25 compromised lifespan and resistance to the fungal pathogen D. coniospora. Double mutants exhibited more severe defects in the lifespan and P. aeruginosa assays, but were similar to the single mutants in other assays. Finally, acs-3 mutants displayed defects in their epidermal surface barrier, potentially accounting for the observed sensitivities. Together, these data indicate that inactivation of either acs-3 or nhr-25 causes stress sensitivity and increased expression of innate immunity/stress genes, most likely by different mechanisms. Elevated expression of these immune/stress genes appears to abrogate the transcriptional signatures relevant to metabolism and development.
          Cover page: Defects in the C. elegans acyl-CoA synthase, acs-3, and nuclear hormone receptor, nhr-25, cause sensitivity to distinct, but overlapping stresses.
          • Article
          • Peer Reviewed
          UC Santa Cruz Previously Published Works (2014)
          Metazoan transcription factors control distinct networks of genes in specific tissues, yet understanding how these networks are integrated into physiology, development, and homeostasis remains challenging. Inactivation of the nuclear hormone receptor nhr-25 ameliorates developmental and metabolic phenotypes associated with loss of function of an acyl-CoA synthetase gene, acs-3. ACS-3 activity prevents aberrantly high NHR-25 activity. Here, we investigated this relationship further by examining gene expression patterns following acs-3 and nhr-25 inactivation. Unexpectedly, we found that the acs-3 mutation or nhr-25 RNAi resulted in similar transcriptomes with enrichment in innate immunity and stress response gene expression. Mutants of either gene exhibited distinct sensitivities to pathogens and environmental stresses. Only nhr-25 was required for wild-type levels of resistance to the bacterial pathogen P. aeruginosa and only acs-3 was required for wild-type levels of resistance to osmotic stress and the oxidative stress generator, juglone. Inactivation of either acs-3 or nhr-25 compromised lifespan and resistance to the fungal pathogen D. coniospora. Double mutants exhibited more severe defects in the lifespan and P. aeruginosa assays, but were similar to the single mutants in other assays. Finally, acs-3 mutants displayed defects in their epidermal surface barrier, potentially accounting for the observed sensitivities. Together, these data indicate that inactivation of either acs-3 or nhr-25 causes stress sensitivity and increased expression of innate immunity/stress genes, most likely by different mechanisms. Elevated expression of these immune/stress genes appears to abrogate the transcriptional signatures relevant to metabolism and development.
            Cover page: Defects in the C. elegans acyl-CoA Synthase, acs-3, and Nuclear Hormone Receptor, nhr-25, Cause Sensitivity to Distinct, but Overlapping Stresses
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