cell polarity

cell polarity

1. cells need to come together and meet with the basement membrane

   • formation of adherens junction
     • other structures then begin to form around the adherens junction
       • Now we have the adherens junction, JAM, PAR, CRB, ZO3 and claudin together physically within the same region of the cell
         • ZO3 brings ZO1 and ZO2 with it
           • occluding and claudin can now associate with the ZO proteins and the tight junction is formed
             • once the tight junction has formed, cells are considered to be polarized
         • JAM1 (tight junction) associates with the adherens junction
           • small GTP proteins (RAC1 and cdc42) are activated
             • PAR, Crumbs and Scrib polarity complexes form
               • PAR complex - PAR6, PAR3 and atypical PKC - PAR3 associates with JAM of the tight junction on the apical side and PKC is activated
                 • Crumbs complex consists of CRB. PALS1 and PATJ - CRB is a transmembrane protein which also binds to cytoskeleton, PASL1 binds to CRB and PAR complex, PATJ binds PLAS1, ZO3 and claudin1
                   • Crib complex consists of SCRIB, LGL and DLG
                     • aPKC phosphorylates proteins causing a change in location, this keeps the Scrib complex in the BL region
     • formation of adherens junction
       • nectins emanate from neighboring cells, each cell exposes lectins and they bind to each other within the extracellular matrix
         • they can form homodimers or heterodimers
           • lectins then bind afadin on the intracellular domain
             • nectin binding in Ca2+ indpendent
               • E-Cadherin then binds beta cetenin on the intracellular domain
                 • beta catenin links to the cytoskeleton (alpha and beta actin) and to alpha catenin which also binds afadin