Meisosomes, folded membrane microdomains between the apical extracellular matrix and epidermis

Apical extracellular matrices (aECMs) form a physical barrier to the environment. In Caenorhabditis elegans, the epidermal aECM, the cuticle, is composed mainly of different types of collagen, associated in circumferential ridges separated by furrows. Here, we show that in mutants lacking furrows, the normal intimate connection between the epidermis and the cuticle is lost, specifically at the lateral epidermis, where, in contrast to the dorsal and ventral epidermis, there are no hemidesmosomes. At the ultrastructural level, there is a profound alteration of structures that we term 'meisosomes,' in reference to eisosomes in yeast. We show that meisosomes are composed of stacked parallel folds of the epidermal plasma membrane, alternately filled with cuticle. We propose that just as hemidesmosomes connect the dorsal and ventral epidermis, above the muscles, to the cuticle, meisosomes connect the lateral epidermis to it. Moreover, furrow mutants present marked modifications of the biomechanical properties of their skin and exhibit a constitutive damage response in the epidermis. As meisosomes co-localise to macrodomains enriched in phosphatidylinositol (4,5) bisphosphate, they could conceivably act, like eisosomes, as signalling platforms, to relay tensile information from the aECM to the underlying epidermis, as part of an integrated stress response to damage

Genetic Mapping and Exome Sequencing Identify Variants Associated with Five Novel Diseases

The Clinic for Special Children (CSC) has integrated biochemical and molecular methods into a rural pediatric practice serving Old Order Amish and Mennonite (Plain) children. Among the Plain people, we have used single nucleotide polymorphism (SNP) microarrays to genetically map recessive disorders to large autozygous haplotype blocks (mean = 4.4 Mb) that contain many genes (mean = 79). For some, uninformative mapping or large gene lists preclude disease-gene identification by Sanger sequencing. Seven such conditions were selected for exome sequencing at the Broad Institute; all had been previously mapped at the CSC using low density SNP microarrays coupled with autozygosity and linkage analyses. Using between 1 and 5 patient samples per disorder, we identified sequence variants in the known disease-causing genes SLC6A3 and FLVCR1, and present evidence to strongly support the pathogenicity of variants identified in TUBGCP6, BRAT1, SNIP1, CRADD, and HARS. Our results reveal the power of coupling new genotyping technologies to population-specific genetic knowledge and robust clinical data

Meisosomes, folded membrane microdomains between the apical extracellular matrix and epidermis

International audienceApical extracellular matrices (aECMs) form a physical barrier to the environment. In Caenorhabditis elegans , the epidermal aECM, the cuticle, is composed mainly of different types of collagen, associated in circumferential ridges separated by furrows. Here, we show that in mutants lacking furrows, the normal intimate connection between the epidermis and the cuticle is lost, specifically at the lateral epidermis, where, in contrast to the dorsal and ventral epidermis, there are no hemidesmosomes. At the ultrastructural level, there is a profound alteration of structures that we term ‘meisosomes,’ in reference to eisosomes in yeast. We show that meisosomes are composed of stacked parallel folds of the epidermal plasma membrane, alternately filled with cuticle. We propose that just as hemidesmosomes connect the dorsal and ventral epidermis, above the muscles, to the cuticle, meisosomes connect the lateral epidermis to it. Moreover, furrow mutants present marked modifications of the biomechanical properties of their skin and exhibit a constitutive damage response in the epidermis. As meisosomes co-localise to macrodomains enriched in phosphatidylinositol (4,5) bisphosphate, they could conceivably act, like eisosomes, as signalling platforms, to relay tensile information from the aECM to the underlying epidermis, as part of an integrated stress response to damage

Necroptosis Drives Motor Neuron Death in Models of Both Sporadic and Familial ALS

Most cases of neurodegenerative diseases are sporadic, hindering the use of genetic mouse models to analyze disease mechanisms. Focusing on the motor neuron (MN) disease amyotrophic lateral sclerosis (ALS), we therefore devised a fully humanized coculture model composed of human adult primary sporadic ALS (sALS) astrocytes and human embryonic stem-cell-derived MNs. The model reproduces the cardinal features of human ALS: sALS astrocytes, but not those from control patients, trigger selective death of MNs. The mechanisms underlying this non-cell-autonomous toxicity were investigated in both astrocytes and MNs. Although causal in familial ALS (fALS), SOD1 does not contribute to the toxicity of sALS astrocytes. Death of MNs triggered by either sALS or fALS astrocytes occurs through necroptosis, a form of programmed necrosis involving receptor-interacting protein 1 and the mixed lineage kinase domain-like protein. The necroptotic pathway therefore constitutes a potential therapeutic target for this incurable disease

Genetically separable functions of the MEC-17 tubulin acetyltransferase affect microtubule organization

Background: Microtubules (MTs) are formed from the lateral association of 11-16 protofilament chains of tubulin dimers, with most cells containing 13-protofilament (13-p) MTs. How these different MTs are formed is unknown, although the number of protofilaments may depend on the nature of the \u3b1- and \u3b2-tubulins. Results: Here we show that the enzymatic activity of the Caenorhabiditis elegans \u3b1-tubulin acetyltransferase (\u3b1-TAT) MEC-17 allows the production of 15-p MTs in the touch receptor neurons (TRNs) MTs. Without MEC-17, MTs with between 11 and 15 protofilaments are seen. Loss of this enzymatic activity also changes the number and organization of the TRN MTs and affects TRN axonal morphology. In contrast, enzymatically inactive MEC-17 is sufficient for touch sensitivity and proper process outgrowth without correcting the MT defects. Thus, in addition to demonstrating that MEC-17 is required for MT structure and organization, our results suggest that the large number of 15-p MTs, normally found in the TRNs, is not essential for mechanosensation. Conclusion: These experiments reveal a specific role for \u3b1-TAT in the formation of MTs and in the production of higher order MTs arrays. In addition, our results indicate that the \u3b1-TAT protein has functions that require acetyltransferase activity (such as the determination of protofilament number) and others that do not (presence of internal MT structures). \ua9 2012 Elsevier Ltd All rights reserved

Microcephaly and chorioretinopathy due to a homozygous <i>TUBGCP6</i> mutation.

<p>(<b>A</b>) An affected infant has marked microcephaly (>4SD below normal), a receding forehead, diminutive anterior fontanelle, and sutural ridging. She has cognitive delay and visual impairment but is socially engaged. (<b>B</b>) Head circumference and length plots for Mennonite microcephaly patients. (<b>C</b>) Brain magnetic resonance imaging (MRI) shows diffuse pachygyria, normal myelination, and (<b>D</b>) a hypoplastic cerebellar vermis.</p

Genetic mapping of seven Plain disorders.

<p>The results of autozygosity mapping using Affymetrix GeneChip 10 K or 50 K SNP microarrays are plotted for each disorder. The x-axis depicts chromosomal location on autosomes. Yellow peaks represent the number of contiguous homozygous SNPs shared by affected individuals and the purple peaks depict location scores. (<b>A</b>) Autozygosity mapping of two affected individuals identified a single, large block of homozygosity on chromosome 6 (yellow peak). Genotyping of 6 unaffected siblings excluded this homozygous block, but identified 12 genomic regions greater than 5 Mb in size (red peaks) that were consistent with linkage in the family. (<b>B</b>) List of genomic regions consistent with linkage in the single nuclear family with infantile parkinsonism-dystonia syndrome. Panels <b>C–H</b> provide mapping plots for the other 6 disorders. For two disorders (<b>C,D</b>), 50 K microarrays were used after 10 K microarrays failed to unequivocally localize the disease gene. The other four disorders (<b>E–H</b>) were mapped with 10 K microarrays.</p

Overexpression of mouse HARS in mIMCD3 cells.

<p>(<b>A</b>) Wild-type N-terminal FLAG-HARS localizes to the cytoplasm. (<b>B</b>) Mutant N-terminal FLAG-HARS (p.Tyr454Ser) localizes to the cytoplasm in a manner that is indistinguishable from the wild-type localization shown in <b>A</b>. Transfected and non-transfected cells were labeled with anti-FLAG M2 monoclonal antibody and AlexaFluor 488-conjugated anti-mouse IgG₁ (green fluorescence). (<b>C</b>) Reaction velocity vs. human tRNA^His concentration for histidine aminoacylation of tRNA^His by wild-type murine HARS (HARS) and p.Tyr454Ser (Y454S) HARS. Scale bar = 10 µm in <b>A</b> and <b>B</b>.</p