Identifying Plectin Isoform Functions through Animal Models

Plectin, a high-molecular-weight cytoskeletal linker protein, binds with high affinity to intermediate filaments of all types and connects them to junctional complexes, organelles, and inner membrane systems. In addition, it interacts with actomyosin structures and microtubules. As a multifunctional protein, plectin has been implicated in several multisystemic diseases, the most common of which is epidermolysis bullosa simplex with muscular dystrophy (EBS-MD). A great part of our knowledge about plectin’s functional diversity has been gained through the analysis of a unique collection of transgenic mice that includes a full (null) knockout (KO), several tissue-restricted and isoform-specific KOs, three double KOs, and two knock-in lines. The key molecular features and pathological phenotypes of these mice will be discussed in this review. In summary, the analysis of the different genetic models indicated that a functional plectin is required for the proper function of striated and simple epithelia, cardiac and skeletal muscle, the neuromuscular junction, and the vascular endothelium, recapitulating the symptoms of humans carrying plectin mutations. The plectin-null line showed severe skin and muscle phenotypes reflecting the importance of plectin for hemidesmosome and sarcomere integrity; whereas the ablation of individual isoforms caused a specific phenotype in myofibers, basal keratinocytes, or neurons. Tissue-restricted ablation of plectin rendered the targeted cells less resilient to mechanical stress. Studies based on animal models other than the mouse, such as zebrafish and C. elegans, will be discussed as well.

First description ofLotmaria passimandCrithidia mellificaehaptomonad stage in the honeybee hindgut

The remodelling of flagella into attachment structures is a common and important event in the insect stages of the trypanosomatid life cycle. Among their hymenopteran hosts,Lotmaria passimandCrithidia mellificaecan parasitizeApis mellifera, and as a result they might have a significant impact on honeybee health. However, there are details of their life cycle and the mechanisms underlying their pathogenicity in this host that remain unclear. Here we show that bothL. passimpromastigotes andC. mellificaechoanomastigotes differentiate into haptomonad stage covering the ileum and rectum of honeybees. These haptomonad cells remain attached to the host surface via zonular hemidesmosome-like structures, as revealed by Transmission Electron Microscopy. Hence, for the first time this work describes the haptomonad morphotype of these species and their hemidesmosome-like attachment inApis mellifera, a key trait exploited by other trypanosomatid species to proliferate in the insect host hindgut.Author summaryIn recent years, the mortality of European Honeybees (Apis mellifera) has risen worldwide due to a variety of factors, including their infection by parasites. Former studies have linked the presence of several trypanosomatids species, beingLotmaria passimandCrithidia mellificaethe most prevalent ones, with this increase in mortality. Although previous studies have shown that trypanosomatid infection reduces the lifespan of bees, there is little information regarding their development in the gut when honeybees become infected. Here, for the first time we describe the haptomonad morphotype of these two trypanosomatid species inA. mellifera. The most characteristic feature of haptomonads is the extensive remodelling of the flagellum and the formation of junctional complexes at the host gut wall. The presence of this morphotype in the honeybee hindgut increases our understanding of the life cycle of these species and their possible pathogenic mechanisms. We found that they can multiply while attached and that their disposition, covering the hindgut walls, could hinder host nutrient uptake and consequently, represent a pathogenic mechanism itself. This attachment could also be a key stage in the life-cycle to prevent the trypanosomatids leaving the host prematurely, ensuring transmission through infective morphotypes.

MAGIs regulate aPKC to enable balanced distribution of intercellular tension for epithelial sheet homeostasis

Constriction of the apical plasma membrane is a hallmark of epithelial cells that underlies cell shape changes in tissue morphogenesis and maintenance of tissue integrity in homeostasis. Contractile force is exerted by a cortical actomyosin network that is anchored to the plasma membrane by the apical junctional complexes (AJC). In this study, we present evidence that MAGI proteins, structural components of AJC whose function remained unclear, regulate apical constriction of epithelial cells through the Par polarity proteins. We reveal that MAGIs are required to uniformly distribute Partitioning defective-3 (Par-3) at AJC of cells throughout the epithelial monolayer. MAGIs recruit ankyrin-repeat-, SH3-domain- and proline-rich-region-containing protein 2 (ASPP2) to AJC, which modulates Par-3-aPKC to antagonize ROCK-driven contractility. By coupling the adhesion machinery to the polarity proteins to regulate cellular contractility, we propose that MAGIs play essential and central roles in maintaining steady state intercellular tension throughout the epithelial cell sheet.

Celsr1 adhesive interactions mediate the asymmetric organization of planar polarity complexes

To orchestrate collective polarization across tissues, planar cell polarity (PCP) proteins localize asymmetrically to cell junctions, a conserved feature of PCP that requires the atypical cadherin Celsr1. We report that mouse Celsr1 engages in both trans- and cis-interactions, and organizes into dense and highly stable punctate assemblies. We provide evidence suggesting that PCP-mutant variant of Celsr1, Celsr1Crsh, selectively impairs lateral cis-interactions. Although Celsr1Crsh mediates cell adhesion in trans, it displays increased mobility, diminishes junctional enrichment, and fails to engage in homophilic adhesion with the wild-type protein, phenotypes that can be rescued by ectopic cis-dimerization. Using biochemical and super-resolution microscopy approaches, we show that although Celsr1Crsh physically interacts with PCP proteins Frizzled6 and Vangl2, it fails to organize these proteins into asymmetric junctional complexes. Our results suggest mammalian Celsr1 functions not only as a trans-adhesive homodimeric bridge, but also as an organizer of intercellular Frizzled6 and Vangl2 asymmetry through lateral, cis-interactions.

Role of Phytocompounds En Route Blood-brain Barrier in Cerebral Ischemia

Aims: Cerebral ischemia is a condition that occurs when the blood vessels in the brain are occluded. Subsequent pathophysiological changes include critical structural and functional damage to the blood-brain barrier. Since remedies for restoring the blood-brain barrier are lacking, alternative methods are important. This study aims to discuss the potential role of phytochemicals in ameliorating blood-brain barrier inflammation and hyperpermeability. Methodology: This literature review is based on information available in open source databases for the scientific community. Results: Phytochemicals offer a large resource for neuroprotective cure. Different categories of phytochemical compounds have provided safer and accessible means of medication. A number of phytochemicals have demonstrated antioxidant and anti-inflammatory properties. The respective mechanisms of action have also been discovered for many. Phytochemicals generally inhibit the classic inflammatory signalling molecules, in addition to other pathways. Phytochemicals also strengthen the tight junctional complexes in the blood-brain barrier. Thus phytochemicals substantially improve the affected blood-brain barrier after cerebral ischemia. Conclusion: Phytochemicals possess useful properties directed towards the healing of the blood-brain barrier in cerebral ischemia and further research may elevate phytochemicals as approved therapeutics.

SNAP23 deficiency causes severe brain dysplasia through the loss of radial glial cell polarity

In the developing brain, the polarity of neural progenitor cells, termed radial glial cells (RGCs), is important for neurogenesis. Intercellular adhesions, termed apical junctional complexes (AJCs), at the apical surface between RGCs are necessary for cell polarization. However, the mechanism by which AJCs are established remains unclear. Here, we show that a SNARE complex composed of SNAP23, VAMP8, and Syntaxin1B has crucial roles in AJC formation and RGC polarization. Central nervous system (CNS)–specific ablation of SNAP23 (NcKO) results in mice with severe hypoplasia of the neocortex and no hippocampus or cerebellum. In the developing NcKO brain, RGCs lose their polarity following the disruption of AJCs and exhibit reduced proliferation, increased differentiation, and increased apoptosis. SNAP23 and its partner SNAREs, VAMP8 and Syntaxin1B, are important for the localization of an AJC protein, N-cadherin, to the apical plasma membrane of RGCs. Altogether, SNARE-mediated localization of N-cadherin is essential for AJC formation and RGC polarization during brain development.