Diverse dystonin gene mutations cause distinct patterns of Dst isoform deficiency and phenotypic heterogeneity in D ystonia musculorum mice

Abstract

Loss-of-function mutations in dystonin (DST) can cause hereditary sensory and autonomic neuropathy type 6 (HSAN-VI) or epidermolysis bullosa simplex (EBS). Recently, DST-related diseases were recognized to be more complex than previously thought because a patient exhibited both neurological and skin manifestations, whereas others display only one or the other. A single DST locus produces at least three major DST isoforms: DST-a (neuronal isoform), DST-b (muscular isoform) and DST-e (epithelial isoform). Dystonia musculorum (dt) mice, which have mutations in Dst, were originally identified as spontaneous mutants displaying neurological phenotypes. To reveal the mechanisms underlying the phenotypic heterogeneity of DST-related diseases, we investigated two mutant strains with different mutations: a spontaneous Dst mutant (Dstdt-23Rbrc mice) and a gene-trap mutant (DstGt mice). The Dstdt-23Rbrc allele possesses a nonsense mutation in an exon shared by all Dst isoforms. The DstGt allele is predicted to inactivate Dst-a and Dst-b isoforms but not Dst-e. There was a decrease in the levels of Dst-a mRNA in the neural tissue of both Dstdt-23Rbrc and DstGt homozygotes. Loss of sensory and autonomic nerve ends in the skin was observed in both Dstdt-23Rbrc and DstGt mice at postnatal stages. In contrast, Dst-e mRNA expression was reduced in the skin of Dstdt-23Rbrc mice but not in DstGt mice. Expression levels of Dst proteins in neural and cutaneous tissues correlated with Dst mRNAs. Because Dst-e encodes a structural protein in hemidesmosomes (HDs), we performed transmission electron microscopy. Lack of inner plaques and loss of keratin filament invasions underneath the HDs were observed in the basal keratinocytes of Dstdt-23Rbrc mice but not in those of DstGt mice; thus, the distinct phenotype of the skin of Dstdt-23Rbrc mice could be because of failure of Dst-e expression. These results indicate that distinct mutations within the Dst locus can cause different loss-of-function patterns among Dst isoforms, which accounts for the heterogeneous neural and skin phenotypes in dt mice and DST-related diseases.

Isoform-specific mutation in Dystonin-b gene causes late-onset protein aggregate myopathy and cardiomyopathy

“…In keratinocytes, plectin and Dst-e localize to the inner plaque of hemidesmosomes and anchor keratin intermediate fibers to hemidesmosomes ( Künzli et al, 2016 ). Conditional deletion of Plec from epidermal cells causes epidermal barrier defects and skin blistering ( Ackerl et al, 2007 ), both of which is more severe than that observed in dt mice carrying Dst-e mutations ( Guo et al, 1995 ; Yoshioka et al, 2020 ). Furthermore, we recently demonstrated that conditional deletion of Dst from Schwann cells in the peripheral nervous system leads to disorganization of the myelin sheath ( Horie et al, 2020 ), similar to that observed for Plec -deficient Schwann cells ( Walko et al, 2013 ).…”

Genetic pain loss disorders

“…Neuronal DST is a cytoskeletal linker protein that interacts with actin, microtubule networks and organelles. Moreover, DST has a role in endoplasmic reticulum (ER) structure and function and in autophagy in different cellular models; however, a direct link to ER-phagy has not been established [19][20][21][22][23][24][25] . DST has multiple tissue-specific isoforms , therefore, DST mutations are associated with various clinical manifestations, including dysautonomia with contractures, psychomotor retardation and motor neuropathy, but also autosomal-recessive epidermolysis bullosa simplex 26,27 .…”

“…[H3] Special features in the molecular diagnostics of CIP/HSAN. HSAN-causing variants affecting noncanonical alternative transcripts and isoform-specific mutations (for example WNK1 and DST gene 19,109 ) can be easily missed by routine NGS diagnostics. Similarly, structural variations including copy number variations (CNV), chromosomal rearrangements and translocations, are commonly missed by panel or exome-wide NGS approaches.…”

Hypolacrimia and Alacrimia as Diagnostic Features for Genetic or Congenital Conditions

“…Recessive Dst pathogenic variations in mice are responsible for dystonia musculorum ( Dst dt ), a sensory neuropathy. 89 Affected mice exhibit ataxia, autonomic disturbances, and ultimately death linked to massive degeneration of the sensory neurons in the dorsal root ganglion. The phenotype is partially rescued by restoring the dystonin-a2 expression in neuronal tissues.…”