Mal de Meleda is an autosomal recessive inflammatory and keratotic palmoplantar skin disorder due to mutations in the ARS B gene, encoding for SLURP-1 (secreted mammalian Ly-6/uPAR-related protein 1). SLURP-1 belongs to the Ly-6/uPAR superfamily of receptor and secreted proteins, which participate in signal transduction, immune cell activation or cellular adhesion. The high degree of structural similarity between SLURP-1 and the three fingers motif of snake neurotoxins and Lynx1 suggests that this protein interacts with the neuronal acetylcholine receptors. We found that SLURP-1 potentiates the human alpha 7 nicotinic acetylcholine receptors that are present in keratinocytes. These results identify SLURP-1 as a secreted epidermal neuromodulator which is likely to be essential for both epidermal homeostasis and inhibition of TNF-alpha release by macrophages during wound healing. This explains both the hyperproliferative as well as the inflammatory clinical phenotype of Mal de Meleda.

SLURP1 is a secreted member of the LY6/PLAUR protein family. Mutations in the SLURP1 gene are the cause of Mal de Meleda (MDM), a rare autosomal recessive genetic disease, characterized by inflammatory palmoplantar keratoderma. In this study, we have analyzed the expression of SLURP1 in normal and MDM skin. SLURP1 was found to be a marker of late differentiation, predominantly expressed in the granular layer of skin, notably the acrosyringium. Moreover, SLURP1 was also identified in several biological fluids such as sweat, saliva, tears, and urine from normal volunteers. In palmoplantar sections from MDM patients, as well as in their sweat, mutant SLURP1, including the new variant R71H-SLURP1, was either absent or barely detectable. Transfected human embryonic kidney 293T cells expressed the MDM mutant SLURP1 containing the single amino-acid substitution G86R but did not tolerate the MDM mutation W15R located in the signal peptide. Thus, most MDM mutations in SLURP1 affect either the expression, integrity, or stability of the protein, suggesting that a simple immunologic test could be used as a rapid screening procedure.

SummaryPhosphatidylinositol (3,4,5)-trisphosphate [PtdIns(3,4,5)P 3 ] is a key regulator of cell signaling that acts by recruiting proteins to the cell membrane, such as at the leading edge during cell migration. Here, we show that PtdIns (3,4,5)P 3 plays a central role in filopodia formation via the binding of myosin-X (Myo10), a potent promoter of filopodia. We found that the second pleckstrin homology domain (Myo10-PH2) of Myo10 specifically binds to PtdIns(3,4,5)P 3 , and that disruption of this binding led to impairment of filopodia and partial re-localization of Myo10 to microtubule-associated Rab7-positive endosomal vesicles. Given that the localization of Myo10 was dynamically restored to filopodia upon reinstatement of PtdIns(3,4,5)P 3 -binding, our results indicate that PtdIns(3,4,5)P 3 binding to the Myo10-PH2 domain is involved in Myo10 trafficking and regulation of filopodia dynamics.

Connexins are homologous four-transmembrane-domain proteins and major components of gap junctions. We recently identified mutations in either GJB3 or GJB4 genes, encoding respectively connexin 31 (Cx31) or 30.3 (Cx30.3), as causally involved in erythrokeratodermia variabilis (EKV), a mostly autosomal dominant disorder of keratinization. Despite slight differences, phenotypes of EKV Mendes Da Costa (Cx31) and EKV Cram-Mevorah (Cx30.3) show major clinical overlap and both Cx30.3 and Cx31 are expressed in the upper epidermal layers. These similarities suggested to us that Cx30.3 and Cx31 may interact at a molecular level. Indeed, expression of wild-type Cx30.3 in HeLa cell resulted only in minor amounts of protein addressed to the plasma membrane. Mutant Cx30.3 was hardly detectable and disturbed intercellular coupling. In sharp contrast, co-expression of both wild-type proteins led to a gigantic increase of stabilized heteromeric gap junctions. Furthermore, co-expressed wild-type Cx30.3 and Cx31 coprecipitate, which demonstrates a physical interaction. Inhibitor experiments revealed that this interaction begins in the endoplasmic reticulum. These results not only provide new insights into epidermal connexin synthesis and polymerization, but also allow a novel molecular explanation for the similarity of EKV phenotypes.

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Images document scientific discoveries and are prevalent in modern biomedical research. Microscopy imaging in particular is currently undergoing rapid technological advancements. However for scientists wishing to publish the obtained images and image analyses results, there are to date no unified guidelines. Consequently, microscopy images and image data in publications may be unclear or difficult to interpret. Here we present community-developed checklists for preparing light microscopy images and image analysis for publications. These checklists offer authors, readers, and publishers key recommendations for image formatting and annotation, color selection, data availability, and for reporting image analysis workflows. The goal of our guidelines is to increase the clarity and reproducibility of image figures and thereby heighten the quality of microscopy data is in publications.

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