NAD+ improves neuromuscular development in a zebrafish model of FKRP-associated dystroglycanopathy.

BACKGROUND: Secondary dystroglycanopathies are muscular dystrophies that result from mutations in genes that participate in Dystroglycan glycosylation. Glycosylation of Dystroglycan is essential for muscle fibers to adhere to the muscle extracellular matrix (myomatrix). Although the myomatrix is disrupted in a number of secondary dystroglycanopathies, it is unknown whether improving the myomatrix is beneficial for these conditions. We previously determined that either NAD+ supplementation or overexpression of Paxillin are sufficient to improve muscle structure and the myomatrix in a zebrafish model of primary dystroglycanopathy. Here, we investigate how these modulations affect neuromuscular phenotypes in zebrafish fukutin-related protein (fkrp) morphants modeling FKRP-associated secondary dystroglycanopathy. RESULTS: We found that NAD+ supplementation prior to muscle development improved muscle structure, myotendinous junction structure, and muscle function in fkrp morphants. However, Paxillin overexpression did not improve any of these parameters in fkrp morphants. As movement also requires neuromuscular junction formation, we examined early neuromuscular junction development in fkrp morphants. The length of neuromuscular junctions was disrupted in fkrp morphants. NAD+ supplementation prior to neuromuscular junction development improved length. We investigated NMJ formation in dystroglycan (dag1) morphants and found that although NMJ morphology is disrupted in dag1 morphants, NAD+ is not sufficient to improve NMJ morphology in dag1 morphants. Ubiquitous overexpression of Fkrp rescued the fkrp morphant phenotype but muscle-specific overexpression only improved myotendinous junction structure. CONCLUSIONS: These data indicate that Fkrp plays an early and essential role in muscle, myotendinous junction, and neuromuscular junction development. These data also indicate that, at least in the zebrafish model, FKRP-associated dystroglycanopathy does not exactly phenocopy DG-deficiency. Paxillin overexpression improves muscle structure in dag1 morphants but not fkrp morphants. In contrast, NAD+ supplementation improves NMJ morphology in fkrp morphants but not dag1 morphants. Finally, these data show that muscle-specific expression of Fkrp is insufficient to rescue muscle development and homeostasis.

Lysosomal degradation of GMPPB is associated with limb-girdle muscular dystrophy type 2T.

OBJECTIVE: GDP-mannose pyrophosphorylase B (GMPPB) related phenotype spectrum ranges widely from congenital myasthenic syndrome (CMS), limb-girdle muscular dystrophy type 2T (LGMD 2T) to severe congenital muscle-eye-brain syndrome. Our study investigates the clinicopathologic features of a patient with novel GMPPB mutations and explores the pathogenetic mechanism. METHODS: The patient was a 22-year-old woman with chronic proximal limb weakness for 9 years without cognitive deterioration. Weakness became worse after fatigue. Elevated serum creatine kinase and decrements on repetitive nerve stimulation test were recorded. MRI showed fatty infiltration in muscles of lower limbs and shoulder girdle on T1 sequence. Open muscle biopsy and genetic analysis were performed. RESULTS: Muscle biopsy showed myogenic changes. Two missense mutations in GMPPB gene (c.803T>C and c.1060G>A) were identified in the patient. Western blotting and immunostaining showed GMPPB and α-dystroglycan deficiency in the patient's muscle. In vitro, mutant GMPPB forming cytoplasmic aggregates completely colocalized with microtubule-associated protein 1 light chain 3-II (LC3-II), a classical marker of autophagosome. Degradation of GMPPB was accompanied by an upregulation of LC3-II, which could be restored by lysosomal inhibitor leupeptin. INTERPRETATION: We identified two novel GMPPB mutations causing overlap phenotype between LGMD 2T and CMS. We provided the initial evidence that mutant GMPPB colocalizes with autophagosome at subcellular level. GMPPB mutants degraded by autophagy-lysosome pathway is associated with LGMD 2T. This study shed the light into the enzyme replacement which could become one of the therapeutic targets in the future study.

Whole exome sequencing identified a novel DAG1 mutation in a patient with rare, mild and late age of onset muscular dystrophy-dystroglycanopathy.

Muscular dystrophy-dystroglycanopathy (limb-girdle), type C, 9 (MDDGC9) is the rarest type of autosomal recessive muscular dystrophies. MDDGC9 is manifested with an early onset in childhood. Patients with MDDGC9 usually identified with defective glycosylation of DAG1, hence it is known as "dystroglycanopathies". Here, we report a Chinese pedigree presented with mild MDDGC9. The proband is a 64 years old Chinese man. In this family, both the proband and proband's younger brother have been suffering from mild and late onset MDDGC9. Muscle biopsy showed that the left deltoid muscle with an advanced stage of dystrophic change. Immunohistochemistry staining of dystrophin, α-sarcoglycan, ß-sarcoglycan and dysferlin are normal. Molecular genetic analysis of the proband has been done with whole exome sequencing. A homozygous novel missense mutation (c.2326C>T; p.R776C) in the exon 3 of the DAG1 gene has been identified in the proband. Sanger sequencing revealed that this missense mutation is co-segregated well among the affected and unaffected (carrier) family members. This mutation is not detected in 200 normal healthy control individuals. This novel homozygous missense mutation (c.2326C>T) causes substitution of arginine by cystine at the position of 776 (p.R776C) which is evolutionarily highly conserved. Immunoblotting studies revealed that a significant reduction of α-dystroglycan expression in the muscle tissue. The novelty of our study is that it is a first report of DAG1 associated muscular dystrophy-dystroglycanopathy (limb-girdle), type C, 9 (MDDGC9) with mild and late age of onset. In Chinese population this is the first report of DAG1 associated MDDGC9.

TIM-1 Mediates Dystroglycan-Independent Entry of Lassa Virus.

Lassa virus (LASV) is an Old World arenavirus responsible for hundreds of thousands of infections in West Africa every year. LASV entry into a variety of cell types is mediated by interactions with glycosyltransferase LARGE-modified O-linked glycans present on the ubiquitous receptor α-dystroglycan (αDG). However, cells lacking αDG are permissive to LASV infection, suggesting that alternative receptors exist. Previous studies demonstrated that the phosphatidylserine (PtdSer)-binding receptors Axl and Tyro3 along with C-type lectin receptors mediate αDG-independent entry. Here, we demonstrate that another PtdSer receptor, TIM-1, mediates LASV glycoprotein (GP)-pseudotyped virion entry into αDG-knocked-out HEK 293T and wild-type (WT) Vero cells, which express αDG lacking appropriate glycosylation. To investigate the mechanism by which TIM-1 mediates enhancement of entry, we demonstrate that mutagenesis of the TIM-1 IgV domain PtdSer-binding pocket abrogated transduction. Furthermore, the human TIM-1 IgV domain-binding monoclonal antibody ARD5 blocked transduction of pseudovirions bearing LASV GP in a dose-dependent manner. Finally, as we showed previously for other viruses that use TIM-1 for entry, a chimeric TIM-1 protein that substitutes the proline-rich region (PRR) from murine leukemia virus envelope (Env) for the mucin-like domain served as a competent receptor. These studies provide evidence that, in the absence of a functional αDG, TIM-1 mediates the entry of LASV pseudoviral particles through interactions of virions with the IgV PtdSer-binding pocket of TIM-1.IMPORTANCE PtdSer receptors, such as TIM-1, are emerging as critical entry factors for many enveloped viruses. Most recently, hepatitis C virus and Zika virus have been added to a growing list. PtdSer receptors engage with enveloped viruses through the binding of PtdSer embedded in the viral envelope, defining them as GP-independent receptors. This GP-independent entry mechanism should effectively mediate the entry of all enveloped viruses, yet LASV GP-pseudotyped viruses were previously found to be unresponsive to PtdSer receptor enhancement in HEK 293T cells. Here, we demonstrate that LASV pseudovirions can utilize the PtdSer receptor TIM-1 but only in the absence of appropriately glycosylated α-dystroglycan (αDG), the high-affinity cell surface receptor for LASV. Our studies shed light on LASV receptor utilization and explain why previous studies performed with α-DG-expressing cells did not find that LASV pseudovirions utilize PtdSer receptors for virus uptake.

Walker-Warburg syndrome and tectocerebellar dysraphia: A novel association caused by a homozygous DAG1 mutation.

OBJECTIVES: To elaborate the imaging phenotype associated with a homozygous c.743C > del frameshift mutation in DAG1 leading to complete absence of both α- and ß-dystroglycan previously reported in a consanguineous Israeli-Arab family. METHODS: We analyzed prenatal and postnatal imaging data of patients from a consanguineous Israeli-Arab kindred harboring the DAG1 mutation. RESULTS: The imaging studies (fetal ultrasound, CT scan and postnatal MRI) demonstrated: flat cortex (abnormally thick with irregular pebbled cortical-white matter border on MRI), hydrocephalus, scattered small periventricular heterotopia and subependymal hemorrhages and calcifications, z-shaped brainstem, and in addition an occipital encephalocele, vermian agenesis, and an elongated and thick tectum (tectocerebellar dysraphia). CONCLUSIONS: The novel association of cobblestone malformation with tectocerebellar dysraphia as part of WWS is characteristic of the homozygous c.743C > del frameshift mutation in the DAG1 gene.

Congenital mirror movements in a patient with alpha-dystroglycanopathy due to a novel POMK mutation.

Dystroglycanopathies are a heterogeneous group of muscular dystrophies often associated with variable brain and eye involvement. Glycosylated alpha-dystroglycan (ADG) plays a key role in the development and stability of basement membranes as well as organizing axon guidance in the central nervous system. Congenital mirror movements, either isolated or in association with several genetic syndromes, are defined as inability to perform unimanual movements. We report an adolescent boy with limb-girdle muscular dystrophy due to ADG deficiency and coexisting congenital mirror movements. Genetic work-up revealed a novel homozygous missense mutation in the protein O-mannose kinase (POMK) gene. To our knowledge, this is the first patient in the literature with POMK mutation and congenital mirror movements.

Integrin and dystroglycan compensate each other to mediate laminin-dependent basement membrane assembly and epiblast polarization.

During early embryogenesis, endodermal γ1-laminin expression is required for basement membrane (BM) assembly, promoting conversion of non-polar pluripotent cells into polarized epiblast. The influence of laminin-111 (Lm111) and its integrin and dystroglycan (DG) receptors on epiblast in embryoid bodies (EBs), a model for differentiation of the embryonic plate, was further investigated. Lm111 added to the medium of EBs initiated conversion of inner nonpolar cell to the polarized epiblast epithelium with an exterior-to-central basal-to-apical orientation. Microinjection of Lm111 into EB interiors resulted in an interior BM with complete inversion of cell polarity. Lm111 assembled a BM on integrin-ß1 null EBs with induction of polarization at reduced efficiency. ß-Integrin compensation was not detected in these nulls with integrin adaptor proteins failing to assemble. A dimer of laminin LG domains 4-5 (LZE3) engineered to strongly bind to α-dystroglycan almost completely inhibited laminin accumulation on integrin ß1-null EBs, reducing BM and ablating cell polarization. When Lm111 was incubated with integrin-ß1/dystroglycan double-knockout EBs, laminin failed to accumulate on the EBs, the EBs did not differentiate, and the EBs underwent apoptosis. Collectively the findings support the hypotheses that the locus of laminin cell surface assembly can determine the axis of epithelial polarity. This requires integrin- and/or dystroglycan-dependent binding to laminin LG domains with the highest efficiency achieved when both receptors are present. Finally, EBs that cannot assemble a matrix undergo apoptosis.

Diagnosis and etiology of congenital muscular dystrophy: We are halfway there.

OBJECTIVE: To evaluate the diagnostic outcomes in a large cohort of congenital muscular dystrophy (CMD) patients using traditional and next generation sequencing (NGS) technologies. METHODS: A total of 123 CMD patients were investigated using the traditional approaches of histology, immunohistochemical analysis of muscle biopsy, and candidate gene sequencing. Undiagnosed patients available for further testing were investigated using NGS. RESULTS: Muscle biopsy and immunohistochemical analysis found deficiencies of laminin α2, α-dystroglycan, or collagen VI in 50% of patients. Candidate gene sequencing and chromosomal microarray established a genetic diagnosis in 32% (39 of 123). Of 85 patients presenting in the past 20 years, 28 of 51 who lacked a confirmed genetic diagnosis (55%) consented to NGS studies, leading to confirmed diagnoses in a further 11 patients. Using the combination of approaches, a confirmed genetic diagnosis was achieved in 51% (43 of 85). The diagnoses within the cohort were heterogeneous. Forty-five of 59 probands with confirmed or probable diagnoses had variants in genes known to cause CMD (76%), and 11 of 59 (19%) had variants in genes associated with congenital myopathies, reflecting overlapping features of these conditions. One patient had a congenital myasthenic syndrome, and 2 had microdeletions. Within the cohort, 5 patients had variants in novel (PIGY and GMPPB) or recently published genes (GFPT1 and MICU1), and 7 had variants in TTN or RYR1, large genes that are technically difficult to Sanger sequence. INTERPRETATION: These data support NGS as a first-line tool for genetic evaluation of patients with a clinical phenotype suggestive of CMD, with muscle biopsy reserved as a second-tier investigation. Ann Neurol 2016;80:101-111.

Absence of α- and ß-dystroglycan is associated with Walker-Warburg syndrome.

OBJECTIVE: To identify the underlying genetic defect in 5 patients from a consanguineous family with a Walker-Warburg phenotype, together with intracranial calcifications. METHODS: Homozygosity mapping and exome sequencing, followed by Sanger sequencing of the obtained candidate gene, was performed. Expression of the candidate gene was tested by reverse transcription PCR. Patient fibroblasts were converted to myotubes, and the expression and function of dystroglycan was tested by Western blotting. RESULTS: We detected a homozygous loss-of-function frameshift mutation in the DAG1 gene and showed that this mutation results in a complete absence of both α- and ß-dystroglycan. CONCLUSIONS: A loss-of-function mutation in DAG1 can result in Walker-Warburg syndrome and is not embryonic lethal.

Distrofias musculares congénitas en el niño / Congenital muscular dystrophies in children

Las distrofias musculares congénitas (DMC) representan desde el punto de vista clínico y genético un grupo heterogéneo de enfermedades dentro de la patología neuromuscular. Las formas más conocidas son: DMC por déficit de merosina, DMC por déficit de colágeno VI, DMC relacionada con LMNA, DMC relacionada con selenoproteína (SEPN1) y las DMC vinculadas a los alfa-distroglicanos. Se presentan con un amplio espectro de fenotipos clínicos. En su mayoría son de herencia autosómica recesiva. Con mucha frecuencia las manifestaciones iniciales comienzan en la infancia o en el período neonatal. Se sospechan clínicamente por la existencia de hipotonía y paresia y se caracterizan por la existencia de un patrón distrófico en la biopsia muscular (sustitución de músculo por tejido fibroadiposo, con necrosis y regeneración celular). Avances en la comprensión de la patogénesis molecular de las DMC han permitido profundizar en la clasificación de los diferentes subtipos. El objetivo de esta revisión es comentar los avances de los últimos años en cuanto a la clasificación de las DMC en relación a la genética, las proteínas involucradas y su presentación clínica (AU)

From the clinical and genetic point of view, congenital muscular dystrophies (CMD) are a heterogenic group of diseases within neuromuscular pathologies. The best known forms are: merosin deficiency CMD, collagen VI deficiency CMD, LMNA-related CMD, selenoprotein-related CMD (SEPN1) and alpha-dystroglycan-related CMD. They present with a broad spectrum of clinical phenotypes. Most of them are transmitted by recessive autosomal inheritance. The initial manifestations very often begin in infancy or in the neonatal period. There are clinical suspicions of the existence of hypotonia and paresis, and they are characterised by a dystrophic pattern in the muscular biopsy (muscle replaced by fibroadipose tissue, with necrosis and cell regeneration). Advances in the understanding of the molecular pathogenesis of CMD have made it possible to make further progress in the classification of the different subtypes. The aim of this review is to comment on the advances made in recent years as regards the classification of CMD in terms of genetics, the proteins involved and their clinical presentation (AU)

[Congenital muscular dystrophies in children]. / Distrofias musculares congénitas en el niño.

From the clinical and genetic point of view, congenital muscular dystrophies (CMD) are a heterogenic group of diseases within neuromuscular pathologies. The best known forms are: merosin deficiency CMD, collagen VI deficiency CMD, LMNA-related CMD, selenoprotein-related CMD (SEPN1) and alpha-dystroglycan-related CMD. They present with a broad spectrum of clinical phenotypes. Most of them are transmitted by recessive autosomal inheritance. The initial manifestations very often begin in infancy or in the neonatal period. There are clinical suspicions of the existence of hypotonia and paresis, and they are characterised by a dystrophic pattern in the muscular biopsy (muscle replaced by fibroadipose tissue, with necrosis and cell regeneration). Advances in the understanding of the molecular pathogenesis of CMD have made it possible to make further progress in the classification of the different subtypes. The aim of this review is to comment on the advances made in recent years as regards the classification of CMD in terms of genetics, the proteins involved and their clinical presentation.

TITLE: Distrofias musculares congenitas en el niño.Las distrofias musculares congenitas (DMC) representan desde el punto de vista clinico y genetico un grupo heterogeneo de enfermedades dentro de la patologia neuromuscular. Las formas mas conocidas son: DMC por deficit de merosina, DMC por deficit de colageno VI, DMC relacionada con LMNA, DMC relacionada con selenoproteina (SEPN1) y las DMC vinculadas a los alfa-distroglicanos. Se presentan con un amplio espectro de fenotipos clinicos. En su mayoria son de herencia autosomica recesiva. Con mucha frecuencia las manifestaciones iniciales comienzan en la infancia o en el periodo neonatal. Se sospechan clinicamente por la existencia de hipotonia y paresia y se caracterizan por la existencia de un patron distrofico en la biopsia muscular (sustitucion de musculo por tejido fibroadiposo, con necrosis y regeneracion celular). Avances en la comprension de la patogenesis molecular de las DMC han permitido profundizar en la clasificacion de los diferentes subtipos. El objetivo de esta revision es comentar los avances de los ultimos años en cuanto a la clasificacion de las DMC en relacion a la genetica, las proteinas involucradas y su presentacion clinica.

Respiratory and cardiac function in congenital muscular dystrophies with alpha dystroglycan deficiency.

The aim of this retrospective study was to assess respiratory and cardiac function in a large cohort of patients with congenital muscular dystrophies (CMD) with reduced glycosylation of alphadystroglycan (α-DG). Thirteen of the 115 patients included in the study died between the age of 1 month and 20 years. The age at last follow up of the surviving 102 ranged between 1 year and 68 years (median: 9.3 years). Cardiac involvement was found in 7 of the 115 (6%), 5 with dilated cardiomyopathy, 1 cardiac conductions defects and 1 mitral regurgitation. Respiratory function was impaired in 14 (12%). Ten of the 14 required non invasive nocturnal respiratory support, while the other four required invasive ventilation. Cardiac or respiratory involvement was found in patients with mutations in FKRP, POMT1, POMT2. All of the patients in whom mutation in POMGnT1 were identified had normal cardiac and respiratory function.

Cardiomyopathy in patients with POMT1-related congenital and limb-girdle muscular dystrophy.

Protein-o-mannosyl transferase 1 (POMT1) is a glycosyltransferase involved in α-dystroglycan (α-DG) glycosylation. Clinical phenotype in POMT1-mutated patients ranges from congenital muscular dystrophy (CMD) with structural brain abnormalities, to limb-girdle muscular dystrophy (LGMD) with microcephaly and mental retardation, to mild LGMD. No cardiac involvement has until now been reported in POMT1-mutated patients. We report three patients who harbored compound heterozygous POMT1 mutations and showed left ventricular (LV) dilation and/or decrease in myocardial contractile force: two had a LGMD phenotype with a normal or close-to-normal cognitive profile and one had CMD with mental retardation and normal brain MRI. Reduced or absent α-DG immunolabeling in muscle biopsies were identified in all three patients. Bioinformatic tools were used to study the potential effect of POMT1-detected mutations. All the detected POMT1 mutations were predicted in silico to interfere with protein folding and/or glycosyltransferase function. The report on the patients described here has widened the clinical spectrum associated with POMT1 mutations to include cardiomyopathy. The functional impact of known and novel POMT1 mutations was predicted with a bioinformatics approach, and results were compared with previous in vitro studies of protein-o-mannosylase function.

Congenital muscular dystrophy type 1D (MDC1D) due to a large intragenic insertion/deletion, involving intron 10 of the LARGE gene.

Mutation of the LARGE gene is the rarest of the six known genetic causes of α-dystroglycanopathy. We report further a family with MDC1D due to a complex genomic rearrangement that was not apparent on standard sequencing of LARGE. Two sisters in a consanguineous family had moderate mental retardation and cerebellar malformations, together with dystrophic changes and markedly reduced α-dystroglycan glycosylation staining on muscle biopsy. There was homozygous linkage to the LARGE locus but sequencing of LARGE coding regions was normal. Analysis of LARGE cDNA showed an abnormal sequence inserted between exons 10 and 11, in most of the transcripts, predicted to introduce a premature stop codon. The abnormal sequence mapped to a spliced EST (DA935254) of unknown function, normally located at 100 kb centromeric of LARGE on chromosome 22q12.3. Quantitative PCR analysis of the EST and adjacent regions showed twice the normal copy number in patients' genomic DNA samples, consistent with a large intra-chromosomal duplication inserted into intron 10 of LARGE in a homozygous state. This insertion was associated with deletion of a central region of intron 10, but the exact break points of the deletion/duplication were not found, suggesting that an even more complex rearrangement may have occurred. The exact function of LARGE, a golgi protein, remains uncertain. POMT and POMGnT enzyme activities were normal in patients' lymphoblast cells, suggesting that defects in LARGE do not affect the initiation of O-mannosyl glycans.

Stress and muscular dystrophy: a genetic screen for dystroglycan and dystrophin interactors in Drosophila identifies cellular stress response components.

In Drosophila, like in humans, Dystrophin Glycoprotein Complex (DGC) deficiencies cause a life span shortening disease, associated with muscle dysfunction. We performed the first in vivo genetic interaction screen in ageing dystrophic muscles and identified genes that have not been shown before to have a role in the development of muscular dystrophy and interact with dystrophin and/or dystroglycan. Mutations in many of the found interacting genes cause age-dependent morphological and heat-induced physiological defects in muscles, suggesting their importance in the tissue. Majority of them is phylogenetically conserved and implicated in human disorders, mainly tumors and myopathies. Functionally they can be divided into three main categories: proteins involved in communication between muscle and neuron, and interestingly, in mechanical and cellular stress response pathways. Our data show that stress induces muscle degeneration and accelerates age-dependent muscular dystrophy. Dystrophic muscles are already compromised; and as a consequence they are less adaptive and more sensitive to energetic stress and to changes in the ambient temperature. However, only dystroglycan, but not dystrophin deficiency causes extreme myodegeneration induced by energetic stress suggesting that dystroglycan might be a component of the low-energy pathway and act as a transducer of energetic stress in normal and dystrophic muscles.

Congenital muscular dystrophies: toward molecular therapeutic interventions.

Congenital muscular dystrophies (CMDs) are a clinically and genetically heterogeneous group of neuromuscular disorders that typically present at birth or in early infancy with hypotonia, weakness, and histologic evidence of a dystrophic myopathy. CMD biochemical types include various abnormalities of alpha-dystroglycan O-mannosyl glycosylation as well as defects in integrin matrix receptors, the extracellular matrix proteins laminin-alpha(2) and collagen VI, nuclear proteins such as lamin A/C, and a protein of the endoplasmic reticulum, selenoprotein N. Current therapies are directed mostly at supportive care; however, recent advances in biotechnology and increased knowledge of the pathophysiology underlying the various CMD types have helped identify potential therapeutic strategies directed at genetic, molecular, and biochemical pathways involved in these disorders. In this article, we review our current understanding of the molecular pathogenesis of several CMD types and how these mechanisms may be therapeutically targeted.

Visual impairment in the absence of dystroglycan.

Ocular involvement in muscular dystrophy ranges from structural defects to abnormal electroretinograms. While the mechanisms underlying the abnormal retinal physiology in patients are not understood, it is thought that alpha-dystroglycan extracellular interactions are critical for normal visual function. Here we show that beta-dystroglycan anchors dystrophin and the inward rectifying K(+) channel Kir4.1 at glial endfeet and that disruption of dystrophin and potassium channel clustering in dystroglycan mutant mice is associated with an attenuation of the electroretinogram b-wave. Glial-specific inactivation of dystroglycan or deletion of the cytoplasmic domain of beta-dystroglycan was sufficient to attenuate the electroretinogram b-wave. Unexpectedly, deletion of the beta-dystroglycan cytoplasmic domain did not disrupt the laminar structure of the retina. In contrast to the role of alpha-dystroglycan extracellular interactions during early development of the CNS, beta-dystroglycan intracellular interactions are important for visual function but not the laminar development of the retina.

Functional diversity of dystroglycan.

During the last 15 years, following its identification and first detailed molecular characterization, the dystroglycan (DG) complex has taken centre stage in biology and biomedicine. Functions in different cells and tissues have been identified for this complex, ranging from its typical role in skeletal muscle as a sarcolemmal stabilizer, highlighted by the recently identified "secondary dystroglycanopathies", to a variety of very diverse functions including embryogenesis, cancer progression, virus particle entry and cell signalling. Such functional promiscuity can be in part explained when considering the multiple domain organization of the two DG subunits, the extracellular alpha-DG and the transmembrane beta-DG, that has been largely scrutinized, but only in part unraveled, exploiting a variety of recombinant and transgenic approaches. Herein, while rapidly recapitulating some of the functions that nowadays can be assigned safely to each DG domain, we also try to envisage a sort of worry list featuring and dwelling on some of the most compelling "mysteries" that should be solved to finally understand DG's functional diversity.