Identification and characterization of DSPIa, a novel isoform of human desmoplakin

Abstract

Desmoplakin is a ubiquitous component of desmosomes and desmosome-like structures, such as the cardiomyocyte area composita. Two major isoforms, desmoplakin I (DSPI) and desmoplakin II (DSPII) are encoded by alternative mRNA transcripts differentially spliced from the same gene. The resulting proteins are identical in amino acid sequence with the exception that DSPII contains only one third of the central alpha-helical rod domain present in DSPI. Here we describe a novel minor isoform of desmoplakin that is also produced by alternative splicing of the desmoplakin gene and that we name desmoplakin Ia (DSPIa). DSPIa is an alternatively spliced DSPI mRNA with a unique splice donor site that is 90% homologous to and downstream of the DSPII specific donor. The resulting DSPIa mRNA is in-frame and encodes a protein that has a central alpha-helical rod domain of intermediate size and that is 156 amino acids larger than DSPII and 443 amino acids smaller than DSPI. We demonstrate, through recombinant expression and short interfering RNA knockdown, that the DSPIa protein is readily detectable, albeit at substantially lower levels than the dominant isoforms, DSPI and DSPII. DSPIa mRNA has a similar tissue distribution to that of DSPI and of DSPII.Electronic supplementary materialThe online version of this article (doi:10.1007/s00441-010-0989-1) contains supplementary material, which is available to authorized users.

The DSPII splice variant is critical for desmosome-mediated HaCaT keratinocyte adhesion

“…siI and siI/II siRNA knockdown of DSP isoforms was performed as previously described (Cabral et al, 2010). siII siRNA knockdown was performed using a trans-splice site strategy, with two siRNA duplexes being designed across the DSPII-specific c.3861-c.5659 RNA junction.…”

“…The DSP haploinsufficiency mutations such as p.Q331X and c.939+1G.A, which cause striate PPK, were modelled by using a siRNA that was described previously (Wan et al, 2007;Cabral et al, 2010) to transiently downregulate all DSP isoforms to about 50% in HaCaT keratinocytes. Cells transfected with this siRNA were designated as siI/II cells.…”

“…Alternative DSP mRNA transcripts encode two major splice variants, desmoplakin I (DSPI) and desmoplakin II (DSPII), and a minor isoform, desmoplakin Ia (DSPIa), which we have recently identified and characterised (Cabral et al, 2010). DSPI and DSPII are expressed at nearly equivalent levels in stratified epithelia such as the epidermis, but DSPI is the predominant isoform in the heart (Angst et al, 1990;Uzumcu et al, 2006).…”

Alopecia, palmoplantar keratoderma, skin fragility and follicular hyperkeratoses due to compound heterozygous mutations in desmoplakin

“…Desmoplakin, the most abundant constituent of the desmosome, is encoded by DSP on chromosome 6p24 and has two main isoforms (DP-I and DP-II), produced by alternative splicing, 1 although a further minor isoform, DP-Ia, has also been described. 2 Inherited mutations in DSP can give rise to a broad spectrum of clinical phenotypes ranging from cutaneous involvement only 3,4 (e.g. skin fragility/woolly hair syndrome 3 ) to full-blown cardiocutaneous syndromes 5-8 necessitating long-term monitoring for possible cardiac muscle dysfunction, arrhythmia or sudden death.…”

Insights into Desmosome Biology from Inherited Human Skin Disease and Cardiocutaneous Syndromes

“…Both are widely expressed in numerous tissues, with DSPII absent from the heart and simple epithelia (Angst et al, 1990). A minor DSP isoform derived from DSPI, named DSPI α , produced by the alternative splicing of DSPI mRNA has also been described, and is detectable in lower levels than those of the dominant isoforms; however, it presents a similar tissue distribution (Cabral et al, 2010b).…”