Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

The 80 S cytoplasmic ribosome is the largest of three populations of ribosomes responsible for protein synthesis in plants. It is comprised of two RNA/protein subunits of unequal size: the small (40 S) subunit selects messages to be translated and performs proofreading, while the large (60 S) subunit has peptidyl transferase acitivity, adding new amino acids to the growing polypeptide. In the model flowering plant <i>Arabidopsis thaliana</i> (hereafter <i>Arabidopsis</i>), four ribosomal RNAs and 81 ribosomal proteins (r-proteins) assemble to form the 80S ribosome. Although the <i>Arabidopsis</i> ribosome contains only a single copy of each of the 81 r-proteins (with the exception of small number of acidic phophoproteins), all r-proteins are encoded from multi-gene families containing two or more expressed members. Herein, I investigated r-protein paralogy in Arabidopsis via specific examination of a two member gene family, RPL23a. By analyzing patterns of reporter gene expression driven by full-length and truncated regulatory regions, I was able to identify a core promoter that is largely conserved between paralogs. Regulation was found to be complex, involving transcriptional, post-transcriptional and translational components. The effects of knocking-out a single RPL23a paralog (RPL23aB) were determined. Results indicated that this paralog is broadly dispensable, and Arabidopsis does not compensate for its loss at the transcriptional level. Subcellular localization was investigated by tagging RPL23aA/B with fluorescent proteins, demonstrating that RPL23aA is targeted to nucleolus more efficiently than RPL23aB, possibly due to a stronger nucleolar localization signal. RNA-interference was used to individually silence RPL23a paralogs to characterize functional overlap. Results showed that RPL23aA, and not RPL23aB, is required for normal development. Mutants with reduced levels of RPL23aA develop a pointed first leaf phenotype that I postulate may be due to disruption of miRNA-mediated degradation of specific auxin response genes. Lastly, the 26 S proteasome was inhibited to determine the importance of protein turnover in regulating RPL23a levels. Findings suggest that proteasome-mediated degradation of RPL23a is essential for preventing accumulation of unincorporated r-proteins. Overall, results indicate that the Arabidopsis RPL23a paralogs have diverged from each other: RPL23aA has become the predominant paralog, while RPL23aB functions in an anciliary capacity and/or is undergoing neofunctionalization.

The 80 S cytoplasmic ribosome is the largest of three populations of ribosomes responsible for protein synthesis in plants. It is comprised of two RNA/protein subunits of unequal size: the small (40 S) subunit selects messages to be translated and performs proofreading, while the large (60 S) subunit has peptidyl transferase acitivity, adding new amino acids to the growing polypeptide. In the model flowering plant <i>Arabidopsis thaliana</i> (hereafter <i>Arabidopsis</i>), four ribosomal RNAs and 81 ribosomal proteins (r-proteins) assemble to form the 80S ribosome. Although the <i>Arabidopsis</i> ribosome contains only a single copy of each of the 81 r-proteins (with the exception of small number of acidic phophoproteins), all r-proteins are encoded from multi-gene families containing two or more expressed members. Herein, I investigated r-protein paralogy in Arabidopsis via specific examination of a two member gene family, RPL23a. By analyzing patterns of reporter gene expression driven by full-length and truncated regulatory regions, I was able to identify a core promoter that is largely conserved between paralogs. Regulation was found to be complex, involving transcriptional, post-transcriptional and translational components. The effects of knocking-out a single RPL23a paralog (RPL23aB) were determined. Results indicated that this paralog is broadly dispensable, and Arabidopsis does not compensate for its loss at the transcriptional level. Subcellular localization was investigated by tagging RPL23aA/B with fluorescent proteins, demonstrating that RPL23aA is targeted to nucleolus more efficiently than RPL23aB, possibly due to a stronger nucleolar localization signal. RNA-interference was used to individually silence RPL23a paralogs to characterize functional overlap. Results showed that RPL23aA, and not RPL23aB, is required for normal development. Mutants with reduced levels of RPL23aA develop a pointed first leaf phenotype that I postulate may be due to disruption of miRNA-mediated degradation of specific auxin response genes. Lastly, the 26 S proteasome was inhibited to determine the importance of protein turnover in regulating RPL23a levels. Findings suggest that proteasome-mediated degradation of RPL23a is essential for preventing accumulation of unincorporated r-proteins. Overall, results indicate that the Arabidopsis RPL23a paralogs have diverged from each other: RPL23aA has become the predominant paralog, while RPL23aB functions in an anciliary capacity and/or is undergoing neofunctionalization.

Understanding the genes that regulate spermatogenesis and steroidogenesis in the testis is critical for enhancement of stallion fertility. Stallion testicular samples were used to identify candidate genes by cDNA microarrays that simultaneously assessed expression levels of 9132 genes. First, gene expression was compared between light (spermatogenically active) and dark (spermatogenically inactive) testis tissue of 1.5-year-old horses (n = 3). Ninety-three genes were differentially expressed (35 light specific, 58 dark specific) in matched paired samples. Second, gene expression was compared between testicular tissue of two mature stallions, one with normal quality semen (fertile) and one with poor quality semen (subfertile). A total of 233 genes were differentially expressed (122 in fertile tissue, 111 in subfertile tissue). Of these, phosphodiesterase 3B (PDE3B), steroidogenic acute regulatory (StAR) protein, and outer dense fiber of sperm tails 2 (ODF2) mRNAs, were localized and quantified by in situ hybridization (ISH) in mature stallions and/or in unilateral cryptorchids. ISH revealed differences (P < 0.05) among mature stallions (n = 10) for PDE3B (localized to seminiferous tubules) and StAR protein (localized to interstitial spaces) mRNAs. A positive correlation coefficient (r = .556, p = .025) was found between StAR protein mRNA and plasma concentration of testosterone. Additionally, both gene products were evaluated in 1-year-old (n = 3) and 3-year-old (n = 3) unilateral cryptorchid stallions. Expression of both PDE3B and StAR protein gene was significantly higher in mature, descended testes compared to mature, retained testes and the descended and retained testes of immature, cryptorchid stallions. StAR protein gene demonstrated significantly higher expression in immature retained testes compared to immature descended testes. A precision-cut tissue slice (PCTS) in vitro culture system was evaluated as a potential tool to study equine testes function. Testes from immature stallions (n = 3) were cut into slices (mean slice weight = 13.85 +/- 0.20 mg; mean slice thickness = 515.00 +/- 2.33 ?m) and exposed to medium containing ovine luteinizing hormone (oLH) at concentrations of 0, 5, 50 and 500 ng/ml for 6 h at 32 degrees C. Medium content of testosterone and estradiol was increased 500% and 120%, respectively, by addition of oLH versus that observed for the testis tissue slices treated with 0 ng oLH (control). An oLH concentration-dependent increase in StAR protein mRNA in tissue slices was detected by in situ hybridization; whereas, differences for PDE3B and ODF2 mRNAs were not observed. Collectively, these results demonstrate that the stallion is an excellent model for studying male fertility due to the initiation of spermatogenesis, frequency of cryptorchidism, and routine castration providing useful tissue to use for studying gene expression.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: TNF-alpha; Type-I IFN; Dengue virus; differential display method. Includes bibliographical references (p. 64-74).

Thesis (Ph.D.)--University of Texas at Arlington, 2009.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains ix, 146 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 111-116).

Thesis (Ph. D.)--University of Missouri--Columbia, 2001. / "May 2001." Typescript. Includes bibliographical references (leaves 109-111). Also available on the Internet.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.