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Open Access Publications from the University of California

Scholarly Works (6 results)

  • Article
  • Peer Reviewed
UC Berkeley Previously Published Works (2020)
The nuclear periphery is a hotspot for the accumulation of age-induced damage in eukaryotic cells. The types of damage that occur at the periphery and their phenotypic consequences have begun to be characterized; however, the mechanisms by which cells repair or eliminate nuclear damage remain poorly understood. Using budding yeast meiosis as a natural system to study cellular rejuvenation, we recently discovered a novel nuclear quality control event, in which age-induced damage is sequestered away from dividing chromosomes to a discarded nuclear compartment that we term the GUNC (for "Gametogenesis Uninherited Nuclear Compartment"). Interestingly, extensive nuclear remodeling occurs even in young cells, including a surprising modularity of the nuclear pore complex, suggesting a general contribution to gamete fitness. In this review, we discuss these findings in the context of recent evidence that the nuclear periphery is a highly dynamic region critical for cellular health.
    Cover page: The dynamic nuclear periphery as a facilitator of gamete health and rejuvenation
    • Thesis
    • Peer Reviewed
    UC Berkeley Electronic Theses and Dissertations (2022)

    The nucleus, the defining organelle of the eukaryotic cell, must be remodeled during every cell division in order to accommodate the division of genetic material. While this remodeling has been extensively studied during mitosis, it remains poorly understood how the nucleus is remodeled during meiosis. In this study, we provide a comprehensive analysis of nuclear behavior during meiosis in the model organism budding yeast. First, we find that the nuclear envelope undergoes a five-way division, forming a nuclear-envelope bound compartment that is excluded from gametes. This compartment, termed the Gametogenesis Uninherited Nuclear Compartment or GUNC, contains nuclear pore complexes (NPCs) in all cells and age-induced damage in old cells. The material sequestered to the GUNC is subsequently eliminated by release of vacuolar proteases, establishing this remodeling event as a novel nuclear quality control mechanism that contributes to meiotic cellular rejuvenation. Second, we find that the NPC undergoes two mechanistically-distinct meiotic remodeling events: partial nuclear basket detachment during meiosis I and full nuclear basket detachment during meiosis II. Meiosis I detachment, which involves Nup60 and its binding partner Nup2, is driven by Polo kinase-dependent phosphorylation of Nup60 at its binding interface with the NPC core. Notably, this remodeling event also occurs in the distantly related Schizosaccharomyces pombe, suggesting basket detachment involves conserved nuclear basket organizational principles and fulfills an important function. Finally, we find that the nuclear permeability barrier is transiently disrupted during meiosis II, driving intermixing of the cytoplasm and nucleoplasm. Since the nuclear envelope stays intact throughout meiosis, regulation of nuclear transport machinery is likely involved in this event. Several meiotic regulators disrupt barrier loss or return, although their precise mechanistic contributions remain unclear. In all, this work establishes the nuclear periphery as a highly dynamic and regulated entity during budding yeast meiosis. Studying the budding yeast meiotic nucleus will continue to improve our understanding of nuclear organization and its contributions to cellular health for years to come.

      Cover page: Characterizing nuclear remodeling during budding yeast meiosis
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2018)
      In Saccharomyces cerevisiae, heterochromatin structures required for transcriptional silencing of the HML and HMR loci are duplicated in coordination with passing DNA replication forks. Despite major reorganization of chromatin structure, the heterochromatic, transcriptionally silent states of HML and HMR are successfully maintained throughout S-phase. Mutations of specific components of the replisome diminish the capacity to maintain silencing of HML and HMR through replication. Similarly, mutations in histone chaperones involved in replication-coupled nucleosome assembly reduce gene silencing. Bridging these observations, we determined that the proliferating cell nuclear antigen (PCNA) unloading activity of Elg1 was important for coordinating DNA replication forks with the process of replication-coupled nucleosome assembly to maintain silencing of HML and HMR through S-phase. Collectively, these data identified a mechanism by which chromatin reassembly is coordinated with DNA replication to maintain silencing through S-phase.
        Cover page: Pivotal roles of PCNA loading and unloading in heterochromatin function
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2019)
        Production of healthy gametes in meiosis relies on the quality control and proper distribution of both nuclear and cytoplasmic contents. Meiotic differentiation naturally eliminates age-induced cellular damage by an unknown mechanism. Using time-lapse fluorescence microscopy in budding yeast, we found that nuclear senescence factors - including protein aggregates, extrachromosomal ribosomal DNA circles, and abnormal nucleolar material - are sequestered away from chromosomes during meiosis II and subsequently eliminated. A similar sequestration and elimination process occurs for the core subunits of the nuclear pore complex in both young and aged cells. Nuclear envelope remodeling drives the formation of a membranous compartment containing the sequestered material. Importantly, de novo generation of plasma membrane is required for the sequestration event, preventing the inheritance of long-lived nucleoporins and senescence factors into the newly formed gametes. Our study uncovers a new mechanism of nuclear quality control and provides insight into its function in meiotic cellular rejuvenation.
          Cover page: Meiotic cellular rejuvenation is coupled to nuclear remodeling in budding yeast
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2018)
          In a previous study we established forward genetics in the choanoflagellate Salpingoeca rosetta and found that a C-type lectin gene is required for rosette development (Levin et al., 2014). Here we report on critical improvements to genetic screens in S. rosetta while also investigating the genetic basis for rosette defect mutants in which single cells fail to develop into orderly rosettes and instead aggregate promiscuously into amorphous clumps of cells. Two of the mutants, Jumble and Couscous, mapped to lesions in genes encoding two different predicted glycosyltransferases and displayed aberrant glycosylation patterns in the basal extracellular matrix (ECM). In animals, glycosyltransferases sculpt the polysaccharide-rich ECM, regulate integrin and cadherin activity, and, when disrupted, contribute to tumorigenesis. The finding that predicted glycosyltransferases promote proper rosette development and prevent cell aggregation in S. rosetta suggests a pre-metazoan role for glycosyltransferases in regulating development and preventing abnormal tumor-like multicellularity.
            • Article
            • Peer Reviewed
            UC Berkeley Previously Published Works (2018)
            In a previous study we established forward genetics in the choanoflagellate Salpingoeca rosetta and found that a C-type lectin gene is required for rosette development (Levin et al., 2014). Here we report on critical improvements to genetic screens in S. rosetta while also investigating the genetic basis for rosette defect mutants in which single cells fail to develop into orderly rosettes and instead aggregate promiscuously into amorphous clumps of cells. Two of the mutants, Jumble and Couscous, mapped to lesions in genes encoding two different predicted glycosyltransferases and displayed aberrant glycosylation patterns in the basal extracellular matrix (ECM). In animals, glycosyltransferases sculpt the polysaccharide-rich ECM, regulate integrin and cadherin activity, and, when disrupted, contribute to tumorigenesis. The finding that predicted glycosyltransferases promote proper rosette development and prevent cell aggregation in S. rosetta suggests a pre-metazoan role for glycosyltransferases in regulating development and preventing abnormal tumor-like multicellularity.
              Cover page: Predicted glycosyltransferases promote development and prevent spurious cell clumping in the choanoflagellate S. rosetta
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