Studies on chromosomal segregation in higher organisms have established a definite relationship between crossing-over and nondisjunction -- the two appear to be inversely correlated. Most of the experiments performed involve segregation from inversion and translocation heterozygotes. [...]

There are numerous different white spotting patterns in the horse, including two of particular interest tobiano and sabino. In the mouse, genetic variation in the gene KIT causes many white spotting patterns. Due to the phenotypic similarity among white spotting patterns in horses and mice, KIT was investigated as the cause of the tobiano and sabino spotting patterns in horses. Initially, the KIT cDNA sequences from horses with several spotting patterns were compared. Three single nucleotide polymorphisms (SNPs) were identified, though none were associated with a spotting pattern. Three novel splicing variants were also observed: exon 17 skipping, exon 18 skipping and alternative splicing of exon 3. Families segregating for a sabino spotting pattern (designated Sabino 1) and exon 17 skipping were discovered. Sequencing revealed a SNP (KI16+1037) within intron 16 that was completely associated with skipping of exon 17. Using a PCR-RFLP for KI16+1037, linkage was discovered for sabino spotting (LOD=9.02 for =0) and presence of the Sabino 1 allele detected in seven breeds. While all horses with this SNP exhibited the Sabino 1 phenotype, some horses with a sabino phenotype did not possess the SNP. This is most likely due to genetic heterogeneity of the phenotype. Fluorescent in situ hybridization (FISH) was used to investigate the possibility of chromosome inversion in the region of KIT. A chromosomal inversion was discovered spanning ECA3q13 to 3q21 using BAC clones containing KIT and other genes in the same region. The ECA3q inversion was completely associated with Tobiano in the eight horses tested by FISH. This inversion may disrupt regulatory sequences of the KIT gene and thereby cause tobiano spotting. Spotting patterns are important to horse breeders for aesthetic as well as economic reasons. Spotting patterns in the horse may also be an interesting scientific model. The two genetic variants discovered in this work are good examples of genetic diversity due to mechanisms other than SNPs. Study of these variants may be valuable for examining the effects of the KIT gene on health traits. In particular, the KIT gene directs many functions of the mast cell, a cell that is involved in the etiology of inflammation.

X-chromosome inactivation achieves dosage compensation of X-linked genes between male (XY) and female (XX) mammals. This process involves the down-regulation of most, but not all genes on one of the two X-chromosomes in the nucleus of each female somatic cell. The mechanism of X-inactivation has yet to be elucidated in full, but is known to involve the noncoding transcript of theXist gene, DNA methylation, histone hypo-acetylation and the condensation of higher order chromatin. Recent studies have established mechanisms linking methylation to repressive chromatin structures through methyl-binding proteins and histone deacetylase complexes. In order to better understand the role of methylation in X-inactivation, the promoters of the human Pyruvate dehydrogenase El a (PDHA1) and the human and murine Norrie disease protein (NDP/Ndp) genes were subjected to direct methylation sequencing, allowing the definition of methylation profiles at nucleotide resolution. The promoter of the PDHA1 gene was found to be hyper-methylated on the inactive X-chromosome and hypo-methylated on the active X-chromosome in agreement with studies at the promoters of other X-linked housekeeping genes. Methylation at the promoters of the NDP/Ndp genes was extensively investigated in a range of primary tissues and cell lines. The Ndp promoter was found to be methylated on both active and inactive X-chromosomes, but hypo-methylated in the proximal promoter exclusively in tissues that expressed the Ndp gene. The NDP promoter was found to be unmethylated on the active X-chromosome and hyper-methylated across the proximal promoter on the inactive X-chromosome in expressing cell lines and human retinal tissues. The novel promoter sequences of the human and murine SMCX/Smcx genes were isolated for comparative analysis and to provide a future resource for studying methylation at the promoters of genes which escape the X-inactivation process. Promoter sequences of the PDHA1, NDPI Ndp and SMCX/Smcx genes were screened for putative transcription factor binding sites and for conserved CpG-dinucleotide content. Promoter-reporter gene constructs for these genes were transfected into mammalian cells establishing that the sequences studied were functional promoters. Artificial methylation of these constructs was shown to repress their promoter activities.

It is becoming increasingly apparent that many of the genes in the class III region of the human Major Histocompatibility Complex encode proteins involved in the immune and inflammatory responses. Furthermore, genetic studies have indicated that genes within the class III region, particularly the telomeric segment containing the TNF gene, could contribute to susceptibility to diseases of immune-related aetiology. To further characterise this region and to identify candidate disease susceptibility genes, two overlapping cosmids, TN62 and TN82, covering an ~82kb segment of DNA around the TNF gene were selected for sequence analysis. The eight known genes in this region have been precisely positioned with the order: Gl/AIF-1, 1C7, LST1 (B144), LTB, TNF, LTA, IKBL, BAT1 (centromere to telomere) and their genomic structures have been defined. Comparison of the Gl genomic region with previously described cDNA and genomic sequences, together with the results of RT-PCR, indicates that three alternative transcripts, Gl, Allograft Inflammatory Factor-1 and Interferon-γ Responsive Transcript-1, are all derived from this gene. The completion of the sequence of 1C7 (D6S2570) has revealed that this gene encodes a putative novel member of the immunoglobulin superfamily. A number of alternatively spliced transcripts of 1C7 were identified by RT-PCR, all of which are expressed in immune-related cell lines. Alternative splicing within the immunoglobulin domain- encoding region was seen to result in possible set switching between an IgV domain and an IgC2 domain. In addition to this, a previously unidentified gene, homologous to a number of V- ATPase G-subunits, has been located 1kb telomeric of IKBL. Lastly, the pseudogene UCRH-L and an AIF-1 gene fragment have been identified in the intergenic region between AIF-1 and 1C7. In order to assess the contribution of loci in this region to disease susceptibility, the genes AIF-1, 1C7, ATP6G and the BAT1 promoter region were subjected to mutation analysis. A total of 28 polymorphisms have been identified, 8 in AIF-1, 10 in 1C7, 7 in ATP6G and 3 in the BAT1 promoter region. Work is at present underway to genotype a number of the identified polymorphisms in control DNAs and in DNA samples from patients with combined variable immunodeficiency (CVID). The information generated from this analysis will bring us closer to explaining the reported linkage of CVID with the telomeric end of the human MHC class III region.

For all organisms, segregation and proper intracellular localization of DNA are essential processes in ensuring faithful inheritance of genetic material. In prokaryotes, several different mechanisms have developed for efficiently moving chromosomal DNA to proper cellular locations prior to cell division, and the same holds true for bacterial plasmids. Low-copy-number plasmids and bacterial chromosomes encode active partition systems to ensure their inheritance within a bacterial cell population. One of the well-studied models of partition is that of the P1 plasmid in E. coli. The partition system encoded by the P1 plasmid is known as parABS - ParA is the partition ATPase, ParB is the partition site binding protein and parS is the partition site. The goal of this thesis was to investigate the nucleoprotein complexes essential in the P1 plasmid partition reaction. First, I examined how a single ParB dimer can bind its complicated arrangement of recognition motifs in parS to initiate the partition reaction. I then characterized a novel ParA interaction with the host nucleoid that is critical for proper P1 plasmid dynamics in vivo. Finally, I demonstrate how ParA can act as an adaptor between the nucleoid and the partition complex; effectively allowing the plasmid to use the nucleoid as a track for its intracellular movement and localization. My thesis work provides evidence towards a model that explains the P1 plasmid partition mechanism.

No description available.

Thesis (MAppSc)--University of South Australia, 1996

Bibliography: leaves 98-136 / viii, 152 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Paediatrics, 1989

Thesis (MAppSc)--University of South Australia, 1996

Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available online.