Cell Biology & Molecular Genetics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2750
Browse
5 results
Search Results
Item Shaping the Dicot Fruit: Molecular and Genomic Approaches to Fruit Development(2016) Hawkins, Charles; Liu, Zhongchi; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The fruit is one of the most complex and important structures produced by flowering plants, and understanding the development and maturation process of fruits in different angiosperm species with diverse fruit structures is of immense interest. In the work presented here, molecular genetics and genomic analysis are used to explore the processes that form the fruit in two species: The model organism Arabidopsis and the diploid strawberry Fragaria vesca. One important basic question concerns the molecular genetic basis of fruit patterning. A long-standing model of Arabidopsis fruit (the gynoecium) patterning holds that auxin produced at the apex diffuses downward, forming a gradient that provides apical-basal positional information to specify different tissue types along the gynoecium’s length. The proposed gradient, however, has never been observed and the model appears inconsistent with a number of observations. I present a new, alternative model, wherein auxin acts to establish the adaxial-abaxial domains of the carpel primordia, which then ensures proper development of the final gynoecium. A second project utilizes genomics to identify genes that regulate fruit color by analyzing the genome sequences of Fragaria vesca, a species of wild strawberry. Shared and distinct SNPs among three F. vesca accessions were identified, providing a foundation for locating candidate mutations underlying phenotypic variations among different F. vesca accessions. Through systematic analysis of relevant SNP variants, a candidate SNP in FveMYB10 was identified that may underlie the fruit color in the yellow-fruited accessions, which was subsequently confirmed by functional assays. Our lab has previously generated extensive RNA-sequencing data that depict genome-scale gene expression profiles in F. vesca fruit and flower tissues at different developmental stages. To enhance the accessibility of this dataset, the web-based eFP software was adapted for this dataset, allowing visualization of gene expression in any tissues by user-initiated queries. Together, this thesis work proposes a well-supported new model of fruit patterning in Arabidopsis and provides further resources for F. vesca, including genome-wide variant lists and the ability to visualize gene expression. This work will facilitate future work linking traits of economic importance to specific genes and gaining novel insights into fruit patterning and development.Item Molecular and Genetic Analysis of Flower Development in Arabidopsis thaliana and the Diploid Strawberry, Fragaria vesca(2012) Hollender, Courtney Allison; Liu, Zhongchi; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In a world with a warming climate and a rapidly growing population, plant biology is becoming a field of increasing importance. Deciphering the molecular and genetic mechanisms behind the development of the flower, the fruit and seed progenitor, will enhance the agricultural productivity needed to ensure a sustainable food supply. My PhD research ties in with this need by furthering the basic knowledge of the mechanisms underlying flower development in two ways. First, using Arabidopsis thaliana, the classic model plant, I investigated the regulation of a gene, SPATULA (SPT), necessary for the proper development of the gynoecium, the female flower organ that, upon fertilization, directly gives rise to fruit. For flower and fruit to properly develop, the expression of SPT, must be tightly regulated both spatially and temporally. My research examined the mechanism of transcriptional repression of SPT in the sepals and petals by several interacting transcription factors (LEUNIG, SEUSS, APETALA2) and the molecular and genetic interaction between ETTIN and SPT in patterning gynoecium. The second focus of my research was to develop Fragaria vesca (the diploid strawberry), as a model Rosaceae for the study of flower and fruit development. Arabidopsis has much value as a small, fast growing, flowering plant with a multitude of genetic and genomic resources, however the flower of this mustard family weed is not representative of all crop flowers. The Rosaceae family, including many agriculturally important fruit trees such as apple, peach, blackberry, and strawberry, warrants its own model plant to investigate the distinct mechanisms behind their unique reproductive biology. Toward developing F. vesca as the model plant for studying Rosaceae flowers, I characterized and described developmental progression of F. vesca flowers morphologically through scanning electron microscopy and histological analysis as well as molecularly through transcriptomes and in situ hybridization. In addition, I pioneered a small-scale mutagenesis screen of F. vesca that will lead to future genetic resources. My thesis work places the groundwork for future discoveries in F. vesca and Rosaceae and benefits research, education, and agricultural applications for the Rosaceae and the plant biology communities.Item Ontogenic and glucocorticoid-regulated gene expression in the developing neuroendocrine system(2010) Ellestad, Laura Elizabeth; Porter, Tom E; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The neuroendocrine system is a critical regulator of vertebrate homeostasis that includes five hypothalamic-pituitary axes which develop during embryogenesis. Adrenal glucocorticoids play an important role in functional maturation of the anterior pituitary through initiation of growth hormone (GH) production. These studies were aimed at characterizing ontogenic and glucocorticoid-regulated changes in gene expression during neuroendocrine system development in the chick. First, to ascertain timing of initiation and establishment of each neuroendocrine axis, we measured mRNA levels of hypothalamic regulatory factors, their pituitary receptors, and pituitary hormones from embryonic day (e) 10 through post-hatch day (d) 7. We found that the adrenocorticotropic axis is the first to be established (e12), followed by establishment of the thyrotropic (e18), somatotropic (e20), lactotropic (d1), and gonadotropic (d5) axes. Next, we examined in detail mechanisms through which glucocorticoids initiate pituitary GH expression during embryogenesis. We determined that glucocorticoids elevate GH mRNA levels on e11 by increasing transcriptional activity of the GH gene rather than enhancing mRNA stability, and protein synthesis, histone deacetylase activity, ras signaling, and ERK1/2 signaling are required for this activation. Conversely, sustained activation of ERK1/2 and p38MAPK pathways reduced glucocorticoid stimulation of GH expression, indicating the requirement for ERK1/2 activity is transitory. Finally, we identified ras-dva as a novel Pit-1 and glucocorticoid-regulated gene in the chicken embryonic pituitary gland. Pituitary ras-dva mRNA levels increased between e10 and e18, decreased just prior to hatch, and remained low or undetectable post-hatch. Ras-dva expression was highly enriched within the pituitary gland on e18, and glucocorticoids rapidly induced ras-dva mRNA in cultured pituitary cells through a mechanism involving transcriptional activation. Potential regulatory elements within the 5'-flanking region of chicken ras-dva responsible for pituitary-specific expression were identified, as was a 2 kb fragment necessary for its glucocorticoid induction in embryonic pituitary cells. These results enhance our understanding of neuroendocrine system development and establishment during embryogenesis, reveal mechanisms underlying glucocorticoid initiation of GH expression in somatotrophs, and identify a new Pit-1 and glucocorticoid target gene that may play an important role in pituitary development.Item Implication of Matrix Metalloproteinases One and Two in Autophagic Cell Death in the Drosophila Salivary Gland(2006-12-06) Kobayashi, Marie; Baehrecke, Eric H; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Programmed cell death plays an important role in normal development. Defects in this process contribute to cancer. Matrix metalloproteinases (MMPs), zinc-dependant endopeptidases that cleave components of the extracellular matrix, are among the multiple protease types implicated in cell death. Here I provide evidence that MMPs function in Drosophila salivary gland cell death. Misexpression of the MMP inhibitor timp inhibited timely salivary gland cell death, while misexpression of mmp2 induced premature salivary gland cell death. mmp RNA interference was inconclusive because salivary gland persistence observed at 28°C was similar to fkh-GAL4 negative controls. MMPs and caspases might have an additive effect, since misexpression of timp and the caspase inhibitor p35 together enhanced salivary gland persistence compared to either timp or p35 misexpression alone. I also provide descriptive confocal microscopy of wild-type salivary glands using ?-Spectrin and the polarity marker Crumbs which suggest that polarity is lost during salivary gland cell death.Item EVOLUTIONARY TRANSITIONS BETWEEN STATES OF STRUCTURAL AND DEVELOPMENTAL CHARACTERS AMONG THE ALGAL CHAROPHYTA (VIRIDIPLANTAE)(2004-12-10) Lewandowski, Jeffrey David; Delwiche, Charles F; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Charophyta comprise green plant representatives ranging from familiar complex-bodied land plants to subtle and simple forms of green algae, presumably the closest phylogenetic relatives of land plants. This biological lineage provides a unique opportunity to investigate evolutionary transition series that likely facilitated once-aquatic green plants to colonize and diversify in terrestrial environments. A literature review summarizes fundamental structural and developmental transitions observed among the major lineages of algal Charophyta. A phylogenetic framework independent of morphological and ontological data is necessary for testing hypotheses about the evolution of structure and development. Thus, to further elucidate the branching order of the algal Charophyta, new DNA sequence data are used to test conflicting hypotheses regarding the phylogenetic placement of several enigmatic taxa, including the algal charophyte genera <i>Mesostigma</i>, <i>Chlorokybus</i>, <i>Coleochaete</i>, and <i>Chaetosphaeridium</i>. Additionally, technical notes on developing RNA methods for use in studying algal Charophyta are included.