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55-140 (56)
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Lecture

EPITHELIUM

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Department
Biological Sciences
Course
55-140
Professor
Habetler
Semester
Fall

Description
EPITHELIUM: Functions as barrier - specialized intercellular junctions - polarized PM (apical and basolateral surfaces) - adhesion to BASAL LAMINA (ECM) which is connected to conn. tiss. basal lamina = basement membrane JUNCTIONAL ADHESION – 1. TIGHT JUNCTIONS (Zona Occludens, ZO) belt of intramembranous particles Components: OCCLUDINS – TM protein CLAUDINS – TM protein (essential) cytoplasmic tail binding proteins Permeability regulation: kinase/phosphatase regulation in response to extracell. stimuli WBC’s can transiently open the TJ’s 2. ANCHORING JUNCTIONS (Adherens, Desmosomes) below TJ on lateral surface epithelia: adherens = zona adherens (BELT) desmosomes = spot junctions cardiac musc.: together in intercalated disks Zona Adherens – CADHERINS regulated by Calcium associate w/ CATENINS, ACTIN in cyto. **cell-cell adhesion  no free B-catenin (TF)  cannot stimulate cell growth** Desomsomal cadherins = DESMOGLEINS/DESMOCOLLINS different cytoplasmic tails  interact with IF’s, not actin plentiful in stressed tissues (skin) 3. GAP JUNCTIONS – for intercellular communication leak-proof channels, common in epithelium 6 conneXIN subunits make a conneXON (usu. identical) 2 connexons to bridge 2nm intercellular gap reversible opening and closing by inserting polar/aromatic residues in GJ reg. by memb. potential, phosphoryl
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