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Author: search.filters.author.Sciascia, MiriamaHas files: Yes

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    Mechanistic target of rapamycin (mTOR) activation during ruminant mammary development and function : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Sciascia, Miriama
    This thesis examines the abundance of total and activated mechanistic target of rapamycin (mTOR) pathway components in the developing and functional ruminant mammary gland. mTOR pathway activation is stimulated by a wide range of intra- and extracellular signals, such as amino acids (AA) and hormones, making the mTOR pathway a potential candidate for the development of intervention strategies designed to increase ruminant lactation potential. Tissues from two trials shown to improve lactation potential; dam-fetal nutrition and exogenous growth hormone (GH) administration during lactation, were used to measure changes in total and activated mTOR pathway protein abundance. Results show mammary glands of d 140 fetal lambs carried by maintenance fed dams and dairy cows administered exogenous GH, had increased abundance of total and activated mTOR and mitogen activated protein kinase (MAPK) pathway proteins. Increased abundance was associated with changes in biochemical indices. In the GH study MAPK pathway activation was stimulated by IGF-1 signaling whilst mTOR pathway activation was proposed to be mediated by AA signalling. Data from the GH study shows, L-arginine a known activator of the mTOR pathway, was the only AA reduced in both plasma and the lactating gland. Upstream factors were not identified for the phenotype observed in the dam-fetal nutrition study, but similar mechanisms were proposed. To elucidate the potential regulation of mTOR pathway activation by L-arginine and examine the effect on milk production, in vitro bovine cell culture models were evaluated. Results show that none of the models evaluated produced a lactating phenotype – a pre-requisite to accurately study the lactating gland in vitro. Finally, this thesis shows L-arginine administration from d 100 to d 140 of pregnancy, in twin bearing ewes had no effect on mTOR protein abundance or activation. However, administration from d 100 to parturition improved maternal gland health. In summary, this thesis associates improved lactation potential with increased total and activated mTOR pathway protein abundance, and the administration of L-arginine during late gestation with improved gland health. These findings provide fundamental knowledge that may lead to the development of novel technologies to increase ruminant gland performance and health.
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    Glucose induced germ tube formation in Candida albicans : a thesis presented to Massey University in fulfilment of the requirements for a Masters of Science degree in Microbiology
    (Massey University, 2004) Sciascia, Miriama
    Candida albicans is an opportunistic fungal pathogen that can cause a wide range of superficial and systemic infections. One of the many factors that have been implicated in C. albicans success as a pathogen is its ability to reversibly switch between a yeast form and a hyphal form (dimorphism). The dimorphic switch is triggered by a wide variety of stimuli which include temperature alone, pH alone, and serum. Serum is a potent inducer of germ tube formation and remains the medium of choice for rapid identification of C. albicans from other non-albicans Candida species. Recently it was shown that, in serum, glucose is the primary inducer of germ tubes in C. albicans strain A72 (Hudson and Farley, unpublished). In this study the ability of glucose, dialysed serum and serum filtrate to induce germ tube formation in a randomly chosen panel of clinical isolates of C. albicans was studied, and the role ot two putative glucose receptors and a putative glucose transporter in the transduction of the glucose signal was investigated. Dialysed serum (molecular weight, > 10 kDa) was less effective (P > 0.05,Students t- test) at inducing germ tube formation than serum. The addition of exogenous glucose alone to dialysed serum restored its ability to induce germ tube formation levels to those seen in serum in seven of the nine clinical isolates tested. Serum filtrate (molecular weight, > 10 kDa) induced germ tubes to levels indistinguishable trom those seen in serum (P > 0.05, Students t-test) in all but one of the clinical isolates tested. Buffered glucose was also able to induce germ tubes in all the clinical isolates tested and the percentage germ tube formation was not statistically significantly different from that obtained with serum in ten out of sixteen clinical isolates tested. The addition of urea to these assays had no statistically significant effect on the induction of germ tube formation. It was proposed that the induction of germ tube formation by glucose was mediated by a surface receptor and therefore the C. albicans genome was examined for genes encoding putative glucose receptors. Identified as possible receptors were orf19.1944 and orf19.5962. Orf19.3668, a putative glucose transporter, was also examined because its expression had been reported to increase during serum induced germ tube formation. Strains carrying homozygous deletions of each ORF were made and the phenotypes of the mutants investigated. None of the ORFs were found to be involved in glucose or serum mediated germ tube formation. However, orf19.1944 was shown to play a role in germ tube formation under embedded conditions.