Browsing by Author "Keyser, Rowena J."

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    Identification of a novel functional deletion variant in the 5'-UTR of the DJ-1 gene
    (BioMed Central, 2009-10) Keyser, Rowena J.; Van der Merwe, Lize; Venter, Mauritz; Kinnear, Craig; Warnich, Louise; Carr, Jonathan; Bardien, Soraya
    Background: DJ-1 forms part of the neuronal cellular defence mechanism against oxidative insults, due to its ability to undergo self-oxidation. Oxidative stress has been implicated in the pathogenesis of central nervous system damage in different neurodegenerative disorders including Alzheimer's disease and Parkinson's disease (PD). Various mutations in the DJ-1 (PARK7) gene have been shown to cause the autosomal recessive form of PD. In the present study South African PD patients were screened for mutations in DJ-1 and we aimed to investigate the functional significance of a novel 16 bp deletion variant identified in one patient. Methods: The possible effect of the deletion on promoter activity was investigated using a Dual- Luciferase Reporter assay. The DJ-1 5'-UTR region containing the sequence flanking the 16 bp deletion was cloned into a pGL4.10-Basic luciferase-reporter vector and transfected into HEK293 and BE(2)-M17 neuroblastoma cells. Promoter activity under hydrogen peroxide-induced oxidative stress conditions was also investigated. Computational (in silico) cis-regulatory analysis of DJ-1 promoter sequence was performed using the transcription factor-binding site database, TRANSFAC via the PATCH™ and rVISTA platforms. Results: A novel 16 bp deletion variant (g.-6_+10del) was identified in DJ-1 which spans the transcription start site and is situated 93 bp 3' from a Sp1 site. The deletion caused a reduction in luciferase activity of approximately 47% in HEK293 cells and 60% in BE(2)-M17 cells compared to the wild-type (P < 0.0001), indicating the importance of the 16 bp sequence in transcription regulation. The activity of both constructs was up-regulated during oxidative stress. Bioinformatic analysis revealed putative binding sites for three transcription factors AhR, ARNT, HIF-1 within the 16 bp sequence. The frequency of the g.-6_+10del variant was determined to be 0.7% in South African PD patients (2 heterozygotes in 148 individuals). Conclusion: This is the first report of a functional DJ-1 promoter variant, which has the potential to influence transcript stability or translation efficiency. Further work is necessary to determine the extent to which the g.-6_+10del variant affects the normal function of the DJ-1 promoter and whether this variant confers a risk for PD.
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    Identifying ligands of the C-terminal domain of cardiac expressed connexin 40 and assessing its involvement in cardiac conduction disease
    (Stellenbosch : University of Stellenbosch, 2007-12) Keyser, Rowena J.; Corfield, Valerie A.; Moolman-Smook, Johanna C.; University of Stellenbosch. Faculty of Health Sciences. Dept. of Biomedical Sciences. Molecular Biology and Human Genetics.
    Connexins (Cx) are major proteins of gap junctions, dynamic pores mediating the relay of ions and metabolites between cells. Cxs 40, 43 and 45 are the predominant cardiac isoforms and their distinct distribution raises questions about their functional differences. Their cytoplasmic (C)-terminal domains are involved in protein-protein interactions. Furthermore, mutations in the myotonic dystrophy protein kinase (DMPK)-causative gene are associated with disruptions in cardiac conduction similar to that described for Cx knock-out mice. DMPK is a Cx43 ligand, raising the possibility that defects in Cx40 ligands may be involved in the development of cardiac conduction disturbances. We hypothesised that delineation of the protein ligands of the C-termini of Cx40 and of Cx45 (parallel study conducted by N Nxumalo) would help elucidate their functional roles. Yeast-two-hybrid methodology was used to identify putative Cx40 ligands. Primers were designed to amplify the C-terminus-encoding domain of the human Cx40 gene (Cx40), the DNA product was cloned into the pGBKT7 vector which was used to screen a cardiac cDNA library in Saccharomyces cerevisiae. Successive selection stages reduced the number of putative Cx40 ligand-containing colonies (preys) from 324 to 33. The DNA sequences of the 33 ligands were subjected to BLAST-searches and internet database literature searches to assign identity and function and to exclude false positive ligands based on subcellular location and function. Eleven plausible ligands were identified: cysteine-rich protein 2 (CRP2), beta-actin (ACTB), creatine kinase, muscle type (CKM), myosin, heavy polypeptide 7 (MYH7), mucolipin1 (MCOLN1), voltage-dependent anion channel 2 (VDAC2), aldehyde dehydrogenase 2 (ALDH2), DEAH box polypeptide 30 (DHX30), NADH dehydrogenase, 6, (NDUFA6), prosaposin (PSAP) and filamin A (FLNA). Cxs 40 and 45 showed differences in the classes of proteins with which they interacted; the majority of putative Cx40 interactors were cytoplasmic proteins, while Cx45 interactors were mitochondrial proteins. These results suggest that Cxs 40 and 45 are not only functionally different, but may also have different cellular distributions. Further analyses of these protein interactions will shed light on the independent roles of Cxs 40 and 45.
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    Investigation of the genetic aetiology of Parkinson's disease in South Africa
    (Stellenbosch : University of Stellenbosch, 2011-03) Keyser, Rowena J.; Bardien, Soraya; Carr, Jonathan; University of Stellenbosch. Faculty of Health Sciences. Dept. of Biomedical Sciences. Molecular Biology and Human Genetics.
    ENGLISH ABSTRACT: Parkinson’s disease (PD), a neurodegenerative movement disorder characterized by resting tremors, bradykinesia, postural instability and rigidity, is due to a selective loss of dopaminergic neurons in the substantia nigra. Non-motoric symptoms include autonomic, cognitive and psychiatric problems. PD has been suggested to result from environmental factors, genetic factors or a combination of the two. Evidence has mounted over the last 13 years supporting the involvement of a significant genetic component. Mutations in the parkin, PINK1, DJ-1, ATP13A2, SNCA, and LRRK2 genes have been conclusively associated with PD. The aim of the present study was to establish the first study on the genetic etiology of PD in South African patients. Patients from the various South African ethnic groups with predominantly early-onset PD and/or a positive family history were recruited. Varying numbers of study participants (ranging from 88-205) were used for the different sections of this study depending on their availability at the time of the experiments and the specific clinical criteria applied. Mutation screening was conducted using High-resolution melt (HRM) analysis, DNA sequencing and multiplex ligation-dependent probe amplification (MLPA). HRM analysis and sequencing of the known PD genes identified the following mutations: parkin (T113fsX163), PINK1 (Y258X), and LRRK2 (G2019S and R1441C). Using haplotype analyses, the five South African LRRK2 G2019S-positive patients were found to share a common ancestor with other G2019S haplotype 1-associated families reported worldwide. Two commercially available MLPA kits, SALSA P051 and P052, were used to assess the study participants for exon dosage mutations. Exonic deletions and insertions in parkin were identified in five patients. In addition, a family with a whole-gene triplication mutation of SNCA was identified. This is the 4th family worldwide to have this specific mutation which leads to a severe phenotype with autonomic dysfunction and early-onset dementia. The CAESAR (CAndidatE Search And Rank) bioinformatic program was used to select novel candidate genes for PD. CAESAR produced a ranked list containing known PD causing genes as well as novel candidates. The MAPT and SNCAIP genes were selected from the list of ten highest scoring genes. HRM analysis identified novel sequence variants in both genes with unknown functional significance that warrants further study. A novel 16bp deletion (g.-6_+10del) in the promoter region of DJ-1 was identified in one PD patient. The functional significance of this variant was investigated using a Dual-Luciferase Reporter assay. The variant was found to significantly reduce luciferase activity in two separate cell lines, HEK293 and BE(2)-M17 neuroblastoma cells, both with and without oxidative stress (p<0.0001), and we proposed that the 16bp sequence might be important in transcriptional regulation of DJ-1. In addition, the activity of three transcription factors (AhR, ARNT and HIF- 1) with binding sites within the deletion sequence may be influenced by the variant. In conclusion, mutation screening resulted in the identification of mutations in six patients in parkin, six patients in LRRK2, one patient in PINK1 and one patient in SNCA. In addition, a number of novel sequence variants were identified with unknown functional significance. Investigating the genetic basis of PD in the unique South African ethnic groups has shown that the known PD associated genes play minor roles in causing the disease in this population which indicates the possible involvement of other as yet unidentified PD genes. Innovative bioinformatic and wet bench experimental strategies are therefore urgently needed to identify new candidate genes for PD.