No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 83-98). Also available in print.

In yeast, aging appears to be marked by a progressive impairment in cellular mechanisms, resulting in irreversible changes in physiology and morphology. To date, very little has been reported about the biochemical changes that occur in yeast as a function of individual cell aging. To investigate this further, six generations of a brewing yeast strain of Saccharomyces cerevisiae (NCYC 1239) were separated according to cellular age using continuous phased culturing and biotin-streptavidin magnetic cell sorting. / To obtain cells with no bud scars (virgin cells), a concentrated yeast slurry was layered onto sucrose density gradients and centrifuged. The uppermost band from the gradients was collected and cells were biotinylated with biotinamidocaproate- N-hydroxysuccinimide ester, that covalently binds to lysine residues on the yeast cell wall. For continuous phased culturing, biotinylated cells were added to a carbon-limited nutrient medium and growth was synchronized using the doubling time of the cells. Harvested cells were incubated with streptavidin superparamagnetic beads and sorted with a strong permanent magnet. In total, approximately 75% of the biotinylated cells were recovered. Viability testing was conducted using vital staining and plate counts, with >98% viability reported with the vital stain and 37% viability with the agar plates. / In conclusion, continuous phased culture, together with magnetic cell sorting has the potential to become a powerful tool for the study of age-related biochemical changes in yeast. Further studies will focus on ensuring the reproducibility of the method and using the recovered cells to study biochemical changes occurring during yeasts' replicative lifespan.

Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 83-98). Also available online.

No description available.

The aging process is unforgiving, targeting a decline in cellular function. Originally, the actin cytoskeleton has not been defined as a hallmark of aging biology, however, numerous studies provide evidence that actin cytoskeleton integrity is declining with age. Mammalian cells express an aged-linked decline in their actin dynamics, consequently defecting their migratory movements, immunological synapse formation, and phagocytosis. Overall, suggesting actin integrity is specifically targeted by aging. Despite the substantial evidence, the underlying mechanism remains elusive, however, current research indicates actin stability as a possible mechanistic aging target. Therefore, our research goal is to further elucidate the mechanism for actin cytoskeleton aging biology in a streamlined model organism, budding yeast, Saccharomyces cerevisiae. Here, we use aging enrichment protocols, streptavidin affinity purification, to isolate a population of older cells to examine any changes in the actin cytoskeleton with age. With an isolated aging population, we analyzed the actin cytoskeleton by testing its stability against a destabilizing drug, Lat-A, and morphology with imaging analysis. We find significant age-associated changes in the actin cytoskeleton, which we later conclude may be a consequence of the age-linked decline in the actin stability that we identified in an aging cell. Additionally, we uncovered a perplexing finding that there is an age-linked decline in actin cable bundling. How actin stability effects actin cable bundling, remains to be determined. However, our actin stability model was further supported by our research characterizing an open reading frame, YKL075C, as a novel actin cable regulatory protein whose deletion: increased actin cable stability, abundance, and mitochondrial quality to extend the replicative lifespan. Upon further insight into YKL075C underlying mechanism, we find YKL075C effects on actin stability and morphology is dependent on alterations in branched-chain amino acid (BCAA) metabolism. Overall, our research discovered a novel actin regulatory protein, Ykl075cp, whose actin function is dependent on BCAA homeostasis, and deleting specifically YKL075C reduces BCAA levels that subsequently increases actin cable stability and abundance to enhance mitochondrial quality and extends longevity.

The Best PhD thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing prize,2006-2007 / published_or_final_version / abstract / Biochemistry / Doctoral / Doctor of Philosophy

B lymphopoiesis in aged mice is characterized by reduced B cell precursors and an altered antibody repertoire. Aged mice maintain an ordinarily minor pool of early c-kit+ pre-B cells, indicative of poor preBCR expression, even as preBCR competent early pre-B cells are significantly reduced. Therefore, in aged mice, preBCR-mediated B2 B lymphopoiesis is significantly diminished; likely as a consequence of poor surrogate light chain expression. Notably, the remnant B1 B cell lineage present in adult bone marrow is retained in aged mice as evidenced by normal numbers (~0.3%) of Lin-CD19+B220low/- B1 B cell precursors. Of interest, B1 progenitors express substantially less lambda 5 surrogate light chain protein than do B2 pro-B cells and the surrogate light chain levels are further reduced in aged mice. B cells derived from putatively preBCR-deficient precursors, either B2 c-kit+ B cell precursors or B1 B cell progenitors, from either young or aged mice, generate new B cells in vitro that are biased to larger size, higher levels of CD43/S7, and decreased kappa light chain expression. Notably, immature B cells in aged bone marrow exhibit a similar phenotype in vivo, consistent with the changes seen in B cell precursor subpopulations. In aged mice, the B2 pathway is partially blocked with limited preBCR expression and signaling; however, continued B cell development via preBCR-deficient pathways, including B1 pathways, is observed. Increased generation of new B cells by these alternative pathways may contribute to altered phenotype, repertoire, and function in senescence.