title: Divergent expression of claudin -1, -3, -4, -5 and -7 in developing human lung.
abstract: BACKGROUND
  Claudins are the main components of tight junctions, structures which are associated with cell polarity and permeability. The aim of this study was to analyze the expression of claudins 1, 3, 4, 5, and 7 in developing human lung tissues from 12 to 40 weeks of gestation.
  
  
  METHODS
  47 cases were analyzed by immunohistochemistry for claudins 1, 3, 4, 5 and 7. 23 cases were also investigated by quantitative RT-PCR for claudin-1, -3 and -4.
  
  
  RESULTS
  Claudin-1 was expressed in epithelium of bronchi and large bronchioles from week 12 onwards but it was not detected in epithelium of developing alveoli. Claudin-3, -4 and -7 were strongly expressed in bronchial epithelium from week 12 to week 40, and they were also expressed in alveoli from week 16 to week 40. Claudin-5 was expressed strongly during all periods in endothelial cells. It was expressed also in epithelium of bronchi from week 12 to week 40, and in alveoli during the canalicular period. RT-PCR analyses revealed detectable amounts of RNAs for claudins 1, 3 and 4 in all cases studied.
  
  
  CONCLUSIONS
  Claudin-1, -3, -4, -5, and -7 are expressed in developing human lung from week 12 to week 40 with distinct locations and in divergent quantities. The expression of claudin-1 was restricted to the bronchial epithelium, whereas claudin-3, -4 and -7 were positive also in alveolar epithelium as well as in the bronchial epithelium. All claudins studied are linked to the development of airways, whereas claudin-3, -4, -5 and -7, but not claudin-1, are involved in the development of acinus and the differentiation of alveolar epithelial cells.
authors.affiliation: Institute of Diagnostics, Department of Pathology and Clinical Research Center, University of Oulu, Oulu, Finland. riitta.kaarteenaho@oulu.fi
authors.forename: Riitta
authors.initials: R
authors.lastname: Kaarteenaho
authors.forename: Heta
authors.initials: H
authors.lastname: Merikallio
authors.forename: Siri
authors.initials: S
authors.lastname: Lehtonen
authors.forename: Terttu
authors.initials: T
authors.lastname: Harju
authors.forename: Ylermi
authors.initials: Y
authors.lastname: Soini
mesh_terms: D001980:Bronchi / Q000737:chemistry / Q000196:embryology; D062445:Claudin-1; D062465:Claudin-3; D062506:Claudin-4; D062507:Claudin-5; D057167:Claudins; D042783:Endothelial Cells / Q000737:chemistry; D018507:Gene Expression Regulation, Developmental; D005865:Gestational Age; D006801:Humans; D007150:Immunohistochemistry; D008168:Lung / Q000098:blood supply / Q000737:chemistry* / Q000196:embryology; D008565:Membrane Proteins / Q000032:analysis* / Q000235:genetics; D011650:Pulmonary Alveoli / Q000737:chemistry / Q000196:embryology; D012333:RNA, Messenger / Q000032:analysis; D020545:Respiratory Mucosa / Q000737:chemistry / Q000196:embryology; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C568108:CLDN1 protein, human; C568122:CLDN3 protein, human; C568157:CLDN4 protein, human; C107466:CLDN5 protein, human; C473255:CLDN7 protein, human; D062445:Claudin-1; D062465:Claudin-3; D062506:Claudin-4; D062507:Claudin-5; D057167:Claudins; D008565:Membrane Proteins; D012333:RNA, Messenger