<p>The Wnt signaling pathway plays a vital role in a multitude of cellular processes across a breadth of multicellular organisms, from simple nematode roundworms such as the Caenorhabditis species to humans. Through the study of this evolutionarily conserved signal transduction pathway in a simple model organism, a greater understanding of the regulation and function of the Wnt pathway can be gained. Emerging research is highlighting the promiscuous nature of Wnt signaling within the network of signaling pathways involved in C. elegans development and aging processes. However, impeding the study of the diverse roles of Wnt signaling in the nematode is the fact that little is known about regulation of key Wnt pathway components in the nematode species, and only a handful of downstream Wnt pathway target genes have been identified. We have used parallel genetic and genomic approaches to elucidate transcriptional targets of the Wnt pathway in C. elegans and the related species C. briggsae. This analysis has uncovered an array of putative Wnt pathway gene targets including pry-1/Axin, a key regulatory component of the pathway. Furthermore, our genome-wide search for Wnt targets has revealed a novel interaction between the Wnt and Hedgehog signaling pathways that is conserved between these two nematode species.</p> / Master of Science (MSc)

The role of cytosine modifications on nuclear transcription has been well characterized, but the function of DNA methylation in the mitochondrial genome has not been determined. Previous studies conducted by the Taylor laboratory have shown overexpression of the mitochondrial isoform of DNMT1 leads to strand-specific changes in gene expression. Here, we show that increased mtDNMT1 expression leads to an increase in the polycistronic transcript encoding the ND1 and Cox1 sequences. In order to understand the mechanistic basis of these changes, we investigated the effects of CpG methylation in the heavy strand promoter on transcription initiation and TFAM binding. Methylation was found to increase transcription initiation from HSP1 and result in larger TFAM:DNA complexes forming at lower protein concentrations. Our data suggest a functional role for cytosine methylation in the mitochondria, which we propose may have an effect on oxidative phosphorylation and cellular function.

Polyamines are small positively charged molecules that control major vital cellular processes including cell growth and proliferation, gene expression, protein production and cell death. Cells can obtain polyamines by making them (biosynthesis) or bringing them into the cell from the outside (transport). Cancer cells require high levels of polyamines to sustain their rapid growth, and depletion of polyamines slows the growth of malignant cells. An FDA approved drug, difluoromethylornithine (DFMO), blocks biosynthesis but is often ineffective because tumor cells respond by increasing transport of polyamines. Thus, a dual therapy that simultaneously targets polyamine biosynthesis and transport is needed. The mechanism of polyamine transport is poorly understood in multicellular eukaryotes and our laboratory focuses on the identification of genes involved in polyamine transport in Drosophila. Our previous work has shown that the transport of polyamines in Drosophila has many similarities to mammalian transport systems, suggesting that Drosophila may be a good model to investigate polyamine transport in mammals. To test this hypothesis, I utilized a novel genetic assay in Drosophila in an attempt to identify positive and negative regulators of polyamine transport. In addition to validating the assay with a gene known to positively regulate polyamine transport, I attempt for the first time to use a strategy designed to identify negative regulators of transport. The major findings are that the Drosophila genes dSLC12A8 and slimfast, which encode cationic amino acid transporters, are required but not essential for polyamine transport. Ultimately, as more components of the polyamine transport system are identified it will be possible to develop drugs that selectively interfere with polyamine transport in mammals and use them in combination therapy with DFMO.

published_or_final_version / abstract / toc / Zoology / Doctoral / Doctor of Philosophy

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Apple (Malus pumila Mill.) and pear (Pyrus communis L.), commonly known as pome fruits, are important deciduous fruit crops in South Africa. The challenges of climate change, disease incidence, distant markets and fluctuating consumer preferences necessitate new cultivars. The Agricultural Research Council (ARC) Infruitec-Nietvoorbij conducts a breeding programme aimed at developing new cultivars that are well adapted, resistant to pests and diseases and good storage potential. A recent review of the pome fruit gene banks, the breeders’ raw material, revealed misidentification and poor characterisation limitating the efficiency of its utilisation. To address these problems, the current study used microsatellite markers to investigate the trueness to type of accessions in the ARC gene banks. In addition, accessions of apple identified as true to type, were genotyped for the ACS1 gene involved with ethylene production and fruit ripening. Two sets of 12 microsatellite markers recommended by a European working group on Pyrus/Malus, one for apple and one for pear, were utilised to fingerprint 540 apple and 197 pear accessions. Eleven and eight of 12 markers, were used respectively to successfully discriminate across the apple and pear accessions, with the exception of clones and sports of particular cultivars. Where possible, fingerprints were compared with those of their reported parents. The use of recommended markers facilitated the comparison of ARC pear accessions with those of the collection in Brogdale (UK). Trueness to type of accessions were established and misidentified accessions were also detected. A similar comparison will be conducted for apple when the Brogdale apple accessions fingerprints become available. Several accessions were found to be false, 78 apple and 22 pear, and removal from the collection was recommended. For ACS1 genotyping of 292 apple accessions, customised fluorescently labelled ACS1-Pr were used rather than the published ACS1-5 primers. Of the 292 apple accessions, 29 were homozygous for the b allele associated with low ethylene and good storage potential. Novel size variation in one allele of the ACS1 gene, was detected in some Malus species and ornamental hybrids. Successful amplification in a multiplex reaction was achieved and proves to be a cost effective method for simultaneous molecular fingerprinting and ACS1 genotyping. True to type material will facilitate confident use of genetic resources in the breeding programmes, and the ACS1 genotypes will identify candidate parents for developing good storage performing cultivars for distant markets. / AFRIKAANSE OPSOMMING: Summary not available

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

No description available.

No description available.

No description available.