Desmosomes are intercellular junctions that connect intermediate filaments (IFs) of adjacent cells within tissues, generating a large and mechanically resilient network. Desmosomes are prominent in epithelia and the myocardium. Their importance for maintenance of the strength and flexibility of these tissues is underlined by mutations in desmosomal genes which compromise skin or heart and in some instances both. This thesis is focused on two obligate plaque proteins of the desmosome, desmoplakin (DP) and plakoglobin (PG), and their role in disease of skin and heart. A novel homozygous nonsense mutation, p.S24X, in the gene encoding PG, JUP, was identified in three non-consanguineous Argentinean patients, resulting in skin fragility, palmoplantar keratoderma (PPK) and woolly hair with no symptoms of cardiomyopathy. p.S24X mRNA was readily detected and an alternative AUG codon translates an N-terminally truncated PG, which is expressed in patient and parental skin samples at barely detectable levels. At the same time another novel homozygous mutation, c.468G>A, was identified in JUP causing a very similar phenotype in two Kuwaiti siblings and resulting also in very low levels of PG in the skin. These results suggest that PG is essential for maintenance of skin integrity, but not for normal heart development in children. The gene encoding DP, DSP, produces two alternative splice variants, DPI and DPII. A novel DP alternative splice isoform, DPIb, is described. As shown by RT-PCR, DSPIb is expressed in several epithelial and cardiovascular tissues and is the only DSP isoform detected in the aorta. Western blotting proteins from HaCaT and K1 cells identified this novel isoform, which has been previously missed due to its similarity in size to DPII. DPIb may help compensate defects in patients with DSPI-specific mutations. The molecular mechanisms of three different DSP mutations leading to skin disease or skin disease associated with cardiomyopathy were investigated. Mutations causing DPI/DPII haploinsufficiency and DPI knock-out lead to decreased expression levels of the desmosomal proteins DSC2, DSC3 and PKP1 in an experimental system using HaCaT keratinocytes. Expression of a mutant DSPI construct harbouring a dominant 30 bp insertion results in the formation of large DPI aggregates at the cell membrane of HaCaT cells. The spectrum of DSP and JUP mutations which cause different clinical phenotypes is discussed.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:528460 |
| Date | January 2010 |
| Creators | Cabral, Rita Meira e Cruz de Vasconcelos |
| Publisher | Queen Mary, University of London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://qmro.qmul.ac.uk/xmlui/handle/123456789/2413 |
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