Download Three Types of Junctions - Wesleyan College Faculty

Three Types of Junctions
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Occluding junctions – Zonula occludens
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restrict and direct movement of fluids in intercellular space
Focal adhesions in a band around cell; composed of
Transmembrane = occludin,
cytoplasmic proteins = ZO 1-3 (1 is tumor supressor, 2 is
part of EGF signaling, 3 is linker)
Breach ZO – leaky epithelia
Most apical attachment, restricting movements of PM
proteins and maintaining integrity of apical vs. basal/lateral
surfaces
Tightness of anastomosing network differs b/w tissues
Three Types of Junctions, cont’d
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Anchoring Junctions (lateral face)
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Zonula Adherens
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Lateral adhesion
Continuous band of transmembrane cadherins bound to
catenin/vinculin/actin on cytoplasmic side
Adhesion is Ca+ dependent
Macula Adherens (Desmosomes)
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High tensile strength
Desmoplakin/plakoglobin attach to intermediate filaments
Not a continuous structure around cell
Attachment plaque – shock absorber
Attach to other cells by desmogleins (cadherin zipper)
Three Types of Junctions, cont’d
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Communicating Junctions
Gap junctions
 Lateral pores composed of connexins
 Pore size alters, but still restricts cell-cell
communication physically
 Lowers electrical resistance in cells (permits ion
passage)
 Protein = Connexin
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Basal Face
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Basement Membrane
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Basal lamina
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Cell-ECM junctions
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Collagen
Proteoglycans
Laminin
Entactin and Fibronectin
H & E stains poorly; use PAS
Beneath Basal Lamina is Reticular lamin (connective tissue)
Attachment, Compartmentalization, Filtration, Polarity induction,
Tissue scaffolding
Focal Adhesions (via actin)
Hemidesmosomes (present in mechanically abraded tissues)
PM foldings
Exocrine Glands
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Merocrine
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Apocrine
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Vesicle bound products; exocytosis
Released in apical portion of cell
Holocrine
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Apoptosis related release (eg., sebaceous glands)