|dc.description.abstract||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||en_US