title: The localisation of the apical Par/Cdc42 polarity module is specifically affected in microvillus inclusion disease.
abstract: BACKGROUND
  Microvillus inclusion disease (MVID) is a genetic disorder affecting intestinal absorption. It is caused by mutations in MYO5B or syntaxin 3 (STX3) affecting apical membrane trafficking. Morphologically, MVID is characterised by a depletion of apical microvilli and the formation of microvillus inclusions inside the cells, suggesting a loss of polarity. To investigate this hypothesis, we examined the location of essential apical polarity determinants in five MVID patients.
  
  
  RESULTS
  We found that the polarity determinants Cdc42, Par6B, PKCζ/ι and the structural proteins ezrin and phospho-ezrin were lost from the apical membrane and accumulated either in the cytoplasm or on the basal side of enterocytes in patients, which suggests an inversion of cell polarity. Moreover, microvilli-like structures were observed at the basal side as per electron microscopy analysis. We next performed Myo5B depletion in three dimensional grown human Caco2 cells forming cysts and found a direct link between the loss of Myo5B and the mislocalisation of the same apical proteins; furthermore, we observed that a majority of cysts displayed an inverted polarity phenotype as seen in some patients. Finally, we found that this loss of polarity was specific for MVID: tissue samples of patients with Myo5B-independent absorption disorders showed normal polarity but we identified Cdc42 as a potentially essential biomarker for trichohepatoenteric syndrome.
  
  
  CONCLUSIONS
  Our findings indicate that the loss of Myo5B induces a strong loss of enterocyte polarity, potentially leading to polarity inversion.
  
  
  CONCLUSIONS
  Our results show that polarity determinants could be useful markers to help establishing a diagnosis in patients. Furthermore, they could be used to characterise other rare intestinal absorption diseases.
authors.affiliation: CNRS, UMR6290, Institut de Génétique et Développement de Rennes, F-35043, Rennes, France.|UEB, SFR Biosit, Faculté de Médecine, University of Rennes 1, F-35043, Rennes, France.
authors.forename: Grégoire
authors.initials: G
authors.lastname: Michaux
authors.affiliation: CNRS, UMR 7288, Developmental Biology Institute of Marseille (IBDM), Aix-Marseille Université, 13288, Marseille, France.
authors.forename: Dominique
authors.initials: D
authors.lastname: Massey-Harroche
authors.affiliation: CNRS, UMR6290, Institut de Génétique et Développement de Rennes, F-35043, Rennes, France.|UEB, SFR Biosit, Faculté de Médecine, University of Rennes 1, F-35043, Rennes, France.
authors.forename: Ophélie
authors.initials: O
authors.lastname: Nicolle
authors.affiliation: Pathology Department, Hôpital Necker-Enfants Malades, Paris, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Rabant
authors.affiliation: Pathology Department, Hôpital Necker-Enfants Malades, Paris, France.
authors.forename: Nicole
authors.initials: N
authors.lastname: Brousse
authors.affiliation: Pediatric Gastroenterology Unit, Hôpital Necker-Enfants Malades, AP-HP, Paris, France.|Sorbonne Paris Cité, Université Paris Descartes, Paris, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Goulet
authors.affiliation: CNRS, UMR 7288, Developmental Biology Institute of Marseille (IBDM), Aix-Marseille Université, 13288, Marseille, France.
authors.forename: André
authors.initials: A
authors.lastname: Le Bivic
authors.affiliation: Pediatric Gastroenterology Unit, Hôpital Necker-Enfants Malades, AP-HP, Paris, France.|Sorbonne Paris Cité, Université Paris Descartes, Paris, France.|Institut Imagine, INSERM U1163, Paris, France.
authors.forename: Frank M
authors.initials: FM
authors.lastname: Ruemmele
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D018938:Caco-2 Cells / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity / Q000502:physiology*; D020895:Enterocytes / Q000378:metabolism; D006801:Humans; D008286:Malabsorption Syndromes / Q000378:metabolism* / Q000473:pathology; D008871:Microvilli / Q000378:metabolism / Q000473:pathology*; D009081:Mucolipidoses / Q000378:metabolism* / Q000473:pathology; D009154:Mutation / Q000235:genetics; D018995:Myosin Heavy Chains / Q000378:metabolism; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics / Q000502:physiology; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C505832:MYO5B protein, human; C556507:PARD6B protein, human; D024701:Myosin Type V; D018995:Myosin Heavy Chains; D020764:cdc42 GTP-Binding Protein
keywords: Celiac disease; Epithelial polarity; MVID; Membrane traffic; Myo5B; Trichohepatoenteric syndrome