The fresh water mollusc Biomphalaria glabrata is the intermediate host for the trematode parasite Schistosoma mansoni, this parasite is responsible for the human disease Schistosomiasis. The significance of B. glabrata in the transmission of schistosomiasis is such that it has been selected for complete genome sequencing. The Biomphalaria glabrata embryonic cell line is an important resource for researchers investigating the interaction between the snail and parasite. The genome of the Bge cells was analysed at the chromosomal level, using DAPI karyotyping. The karyotype revealed extensive aneuploidy, whereby a modal chromosome complement of 63 and 67 was observed in two isolates of the Bge cells, which exceeds B. glabrata’s 2n=36 chromosome number. Indeed, in addition to characterising the Bge cell chromosomes, a method was established for mapping single copy B. glabrata genes onto the chromosomes from the Bge cells using fluorescence in situ hybridisation. Despite the Bge cell’s inherent aneuploidy, the four genes mapped onto diploid homologous chromosomes. This methodology will be an important resource for the genome sequencing consortium. The interphase nucleus is an organised organelle, whereby chromosomes and gene loci have been shown to be located non-randomly and hence it is hypothesised that the organisation of the interphase nucleus is pertinent to the function of the genome. Since there is no data on how the genes of the snail genome behaves in interphase, it was assessed in the Bge cells line. Again, this is important for the sequencing initiative, but also for evolutionary biology. Radially distributed chromosome territories were observed in the nuclei of the Bge cells. The territory position was organised according to territory size, with small chromosome territories positioned towards the interior and large territories intermediately located. In addition, four B. glabrata genes were positioned non-randomly in the interphase nuclei of the Bge cells, again emphasising organised positioning of the genome. With co-culture of S. mansoni miracidia with the Bge cells there is up regulation of specific genes known to be involved in the host response to parasite. These genes are dramatically relocated within the interphase nuclei, implying that these are specific parasite induced nuclear events. An analysis of the genomic distribution of specific histone modified chromatin in the interphase nuclei of B. glabrata, revealed different nuclear distribution of modified chromatin. Indeed, a statistically significant difference in these patterns was observed between juvenile and adult snails, indicating developmental differences in the organisation of the snails’ genome. These differences maybe relevant to the snails’ resistance/susceptibility to the parasite.

Previous theoretical work on DNA replication neglected how the starting points (origins) take their place and how replication time is a ected when origins fail to activate. It is however crucial that origin loci are chosen so that too large gaps between them are avoided; otherwise the time until completion of chromosome replication becomes much longer than is allowed by the cell cycle. We investigate what the optimal origin location should be depending on the likelihood of origins failing. We show analytically and numerically that there exist regimes for origins, either to be positioned together in groups spaced far away from the next, or as equally scattered single origins depending on the uncertainty when activation occurs. The model reproduces origin distributions of frog embryos which are thought to be random, and shows contrarily that grouping must occur in order to swiftly complete replication; known as the random completion problem. The model also holds when considering a circular DNA topology for archaeal genomes, as well as if applied to the whole replication pro ling data of yeast. We study how an optimal origin distribution can arise and propose a mechanism to solve the random completion problem. We show that regular spacing emerges as an inherent property of the car parking model. We introduce a spatial requirement for origins to bind to DNA; origins occupy space on the DNA and can only bind stably if there is su cient space for them. Such a model leads to a well ordered origin distribution with minimal gaps as required for on time DNA replication in frog embryos. The optimal origin distribution emerges directly from our model because origins have a higher chance to bind to large empty regions instead of small once, therefore destroying large inter origin gaps. We also introduce a model to account for the interaction of replication forks with each other which leads to their assembly into replication factories. We show using Boltzmann statistics that their assembly is stochastic. A rst model only considers two pairs of forks which we then extend to describe properties of measured experimental distributions such as fork numbers per factory during on a whole yeast genome approach. Our in silico distribution of forks per factory matches in vivo data well; which suggests that active forks encounter each other randomly for an association into replication factories.

published_or_final_version / Medicine / Master / Doctor of Medicine

published_or_final_version / Biochemistry / Master / Master of Philosophy

The cell's nucleus contains DNA in the form of chromosomes, which are the hereditary content of the organism. The proper transmission of DNA from one generation to the next is critical. Along with this crucial process, cells will also need to transcribe the DNA, silence certain genes (or whole chromosomes) during development and regulate other chromosome dynamics that are still being identified. The molecular components responsible for these processes are starting to be identified. However, the regulation of these components and how they interact with each other is not well understood.The condensin complex is one component that has been identified to play a role in chromosome dynamics. Activity of the complex has been studied in vitro but in vivo activity has been difficult to measure. Similarly, understanding the regulation of the complex has been difficult given the lack of assays and that the complex is essential for cell survival. In this dissertation, I have identified and characterized a regulator of condensin II function using Drosophila melanogaster. The chromo-domain protein Mrg15 interacts with condensin II to inhibit homologous chromosome interactions.Lastly, I look at the role of condensin II in female meiosis. Meiosis involves pairing and subsequent segregation of homologous chromosomes. The process of the initial pairing has remained elusive but specialized structures have evolved to maintain this pairing. Condensin II can antagonize a basal level of homologous pairing and also removes the specialized structure that pair meiotic chromosomes. This dissertation will add to the growing knowledge of the regulation of the condensin II complex and its role in female meiosis.

No description available.

No description available.

No description available.

The purpose of this research was to examine four selected human population groups, institutionalized and normal, to determine the prevalence of the 47, XYY chromosome abnormality among adult males.

The isolation and characterisation of sequences from the X and Y chromosomes will give some insight into the evolutionary relationship between these chromosomes, and may be of use in the study of X-linked disorders. The availability of cDNA and genomic sequences for the human STS locus (associated with the disorder, X-linked ichthyosis) has allowed a preliminary investigation of this locus in man and other species. The localisation of these sequences to Xp22.3, provides confirmation of the sub-regional assignment of the structural gene for STS. STS homologous sequences have been identified on the long arm of the Y chromosome. These sequences also appear present on the X and Y chromosomes of the chimpanzee. In other higher primates, they appear to be X-, but not Y-, linked, suggesting that the situation in man and chimpanzee is the result of a rearrangement between the X and Y chromosomes during the past 15 million years. Another region of X Y homology has been analysed. The locus DXYS27 maps to Yp and Xq21. Restriction enzyme analysis and direct sequence comparison has shown the two loci to be «99% homologous. Phylogenetic studies suggest that the locus is X-, but not Y-, linked in the chimpanzee, suggesting an evolutionarily recent transposition of material from the X to the Y chromosome. The mutations resulting in the X-Y differences appear to have occurred on both the X and Y chromosomes. It has been possible to demonstrate that the Y-specific locus is transferred to the X chromosome in many, but not all, aberrant X-Y interchanges resulting in XX maleness. A sequence has been isolated that detects a hypervariable locus at Xp11.3→Xcen (DXS255) . The hypervariability appears to be due to the presence of a tandemly repeated sequence of variable length. Attempts to clone this repeat have been unsuccessful, as it appears to be unstable in the vector/host systems employed. This sequence will be of value in linkage studies of disease loci known to be present in this region. Hypervariability at this locus has not been identified in other species, suggesting that the repeat sequence is an evolutionarily recent acquisition by the X chromosome. Taken together, the results obtained suggest that the simple model predicting an ancient origin for the bulk of the Y chromosome will have to be reassessed.