Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Subject: search.filters.subject.Developmental Biology

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Now showing 1 - 4 of 4
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    CO-CULTURE OF BONE MARROW STROMAL CELLS AND CHONDROCYTES FOR BONE TISSUE ENGINEERING: MICROARRAY STUDY OF CHONDROCYTE SECRETED FACTORS
    (2011) Janardhanan, Sathyanarayana; Fisher, John P; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Tissue engineering refers to the assembly of biomaterials, cells and signaling molecules to develop functional tissues based on strategies derived from developmental processes. Cells play a crucial role, in that they can secrete a library of molecules, not entirely characterized in the laboratory, and yet provide repeatable results during in vitro experiments. Under conditions of co-culture with mesenchymal stem cells, the underlying biology of chondrocytes can elucidate the signal expression during the early bone development process called endochondral ossification. This interaction is tightly regulated in chondrocytes and results in the recruitment and differentiation of mesenchymal stem cells (MSCs) into osteoblasts. We executed a co-culture system, to observe the potential of alginate encapsulated bovine articular cartilage chondrocytes to induce osteogenic differentiation of bovine bone marrow stromal cells and to observe the interaction on a global scale by making use of the microarray platform. We identified certain genes expressed by chondrocytes that show substantial activity in co-culture systems such as versican (VCAN), secreted frizzled related protein 1 (SFRP1), matrix metallopeptidase 13 (MMP13), extracellular matrix protein 1 ( ECM1) and collagen type 1 ( Col1A1, Col1A2).
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    GENETIC AND MOLECULAR ANALYSIS OF GERMLINE SEX DETERMINATION IN CAENORHABDITIS BRIGGSAE, A MODEL FOR THE CONVERGENT EVOLUTION OF HERMAPHRODITISM
    (2010) Doty, Alana V.; Haag, Eric S.; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Though sex determination and differentiation are critical biological processes, genetic mechanisms that specify sex have undergone profound and rapid evolutionary change across taxa. We may be able to infer processes that generate sex determination diversity by examining closely related species. Within the nematode genus Caenorhabditis, two species, C. elegans and C. briggsae, are androdioecious, producing self-fertile hermaphrodites and males; other Caenorhabditis species generate males/females. Interestingly, phylogenies reveal that C. elegans and C. briggsae independently acquired hermaphroditism, a relatively rare adaptation among animals. In this work, I describe differences in germline sex determination between C. elegans and C. briggsae that may help reveal the molecular basis of their convergent evolution of hermaphroditism. I first describe mutations in the pleiotropic, STAR family RNA-binding protein Cbr-GLD-1 that affect germline sex in C. briggsae. I find that C. briggsae gld-1 mutant hermaphrodites have a sex determination phenotype opposite to that of C. elegans: masculinized versus feminized germlines. I demonstrate that Cbr-GLD-1 coding-plus-regulatory sequences can rescue Ce-gld-1 null animals, arguing that this change in sex determination is not due to changes in GLD-1 function or expression. I further show that gld-1's role in regulating oogenesis is conserved across the Elegans group of Caenorhabditis, demonstrating that the oogenesis function of gld-1 is likely ancient, whereas its sperm-repressing role in C. briggsae has evolved recently. To identify mRNA targets of Cbr-GLD-1 that might be responsible for its sex determination function in C. briggsae, I use an in vivo genome-wide approach to isolate mRNAs associated with Cbr-GLD-1, including potential sex determination targets. I identify 800 putative mRNA targets and confirm specificity of this gene set via qRT-PCR and RNAi. Next, to reveal the roles of GLD-1 in evolutionary context, I create a phylogeny of STAR proteins across metazoans. Finally, I characterize a single feminizing allele recovered through forward screens in C. briggsae for germline sex determination mutants. This work thus begins to dissect the molecular and genetic basis of hermaphroditism in C. briggsae and contributes to a growing body of research on the evolution of germline sex determination differences between C. elegans and C. briggsae.
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    Investigating the roles of OCT4 and CDX2 in directing bovine trophectoderm lineage development
    (2010) Schiffmacher, Andrew Thomas; Keefer, Carol L; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Domestic animal embryo technologies would benefit from a better understanding of the molecular mechanisms that direct early embryonic development. Failure to establish a normal transcriptional regulatory program in the early trophectoderm of nuclear transfer or in vitro derived bovine embryos has been implicated as an underlying cause of placental abnormalities and fetal death. Misexpression of trophoblast–specific genes in these embryos has been identified, but the functions and roles of these genes remain poorly understood. The main focus of this study was to study genes involved in bovine trophectoderm lineage development using the bovine trophectoderm derived CT–1 cell line as a genetic model. Specifically, we investigated the roles of the regulatory transcription factors OCT4 and CDX2 in directing the developmental program of the early bovine trophectoderm via gene regulation of other trophectoderm–specific transcription factors. First, we overcame certain technical limitations of CT–1 cells by improving nucleic acid transfection, CT–1 cell dispersal, and culture protocols, demonstrating for the first time that overexpression assays using Lipitoid are feasible in the hard–to–transfect CT–1 cell line. We expanded the list of trophoblast genes known to be expressed in CT–1 cells and determined that the expression profile was similar to that of the ovoid stage of bovine pre–attachment embryogenesis. We measured relative levels of these genes in response to OCT4 and CDX2 overexpression and knockdown. Our results indicated that CDX2 may be a regulator of transcription of many bovine trophoblast genes and should be the focus of further study. We identified a novel OCT4 retrocopy transcribed into both sense and natural antisense transcripts, which may have a role in post–transcriptionally regulating OCT4 expression within the early bovine trophoblast. Together, these studies validate the CT–1 cell line as an appropriate genetic model for studying gene regulation in the bovine trophectoderm.
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    POLLEN TUBES FAIL TO TARGET OVULE IN THE ABSENCE OF TWO CATION/PROTON EXCHANGERS IN ARABIDOPSIS
    (2010) Lu, Yongxian; Sze, Heven; Cell Biology & Molecular Genetics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Flowering plant reproduction requires precise delivery of the sperm cells to the ovule by a pollen tube. Guiding signals from female cells are being identified, though how pollen senses and responds to those cues are largely unknown. Here I provide genetic evidence that two predicted cation/proton exchangers expressed in Arabidopsis pollen play essential roles in pollen targeting of ovules. Male fertility was unchanged in single chx21 or chx23 mutant pollen; however, male-specific gene transmission was blocked in chx21chx23 double mutant. Wild-type pistil provided with a limited amount of pollen containing a mixture of single and double mutant produced ~60% less seeds compared to that produced with chx23 single mutant pollen, indicating that chx21chx23 pollen is infertile. The double mutant pollen, visualized by a pollen-specific promoter-driven GUS activity, germinated and extended a tube down the transmitting tract, but the tube failed to turn and target an ovule. Unlike wild-type pollen that targeted isolated ovules in a semi-in vivo assay, tube guidance in chx21chx23 pollen was compromised. As a first step to understand the cellular and molecular bases of tube guidance, membrane localization and activity of CHX23 was determined. GFP-tagged CHX23 was localized to endomembranes, predominantly endoplasmic reticulum (ER), in elongating pollen tubes. Furthermore, expression of CHX23 in E. coli resulted in enhanced K+ accumulation at alkaline pH, suggesting a role for CHX23 in K+ acquisition and pH homeostasis. Based on these studies and observations by others that ER oscillates and enters the apex, a simple model is proposed: Modification of localized pH by CHX21 or CHX23 enables pollen tube to sense female signals and respond by shifting directional growth at the funiculus and micropyle to target pollen tip growth towards the ovule.