definition -introduction-cadherins-integrins-igCAMS

1. CAMs
Vimal priya subramanian

2. Adhesion molecules
 Different types of adhesion molecules exist to do different tasks.
 All cell adhesion molecules spend some time at the cell surface.
 All act by binding to particular ligands
Homophilic
 (i.e. adhesion molecules bind themselves on another cell
surface)
Heterophilic
 (i.e. bind to a molecule of a different structure).
May/may not be Ca

3.  Integrins
May link a cell to the extracellular matrix and have a role in cell migration
 Cadherins
May form very stable cell-cell adhesions
 Selectins
May be involved in very rapid transient interactions

4. Cadherins
Cadherins
 Large family of cell surface proteins (>100 members) that mediate Ca
dependent cell-cell adhesion.
 All members have the characteristic cadherin extracellular repeat.
They have a critical role in
 Morphogenesis.
 Cell recognition & sorting
 Boundary formation and maintenance-
 Cordinated and cell movement

5.  In adults , cadherins are responsible for tight cell-cell associations in
tissues.
 They are intimately associated with the cytoskeleton, interacting via
other proteins with both microfilaments (actin) and intermediate
filaments (keratins)
 Blocking cadherin function can prevent the formation of tissues and cause
cells to disaggregate

6.  Different cadherins are expressed on different tissues both in the adult
and in the embryo. For example,
 E-cadherin-on all mammalian embryos, in adults restricted to epithelia
 P-cadherin -on placenta, sticks placenta to uterus.
 N-cadherin-on cells of developing nervous system- is first seen on
mesodermal.
 R-cadherin-critical in formation of the retina

7.  B-adherin -on many nerual structures
 EP-cadherin (C-cadherin maintains adhesion between the blastomeres is
required for the normal movements of gastrulation
 Protocadherins-differ from the classic cadherins by lacking connections to
cytoskeleton through catenins

8. Integrins
 Integrins: Involved in cell-extracellular matrix adhesion and cell-cell
adhesion.
 Integrins are found in invertebrates as well as vertebrates.
 Greatest diversity is in mammalian integrins.
 Structure: heterodimer consisting of two transmembrane glycoprotein
subunits (α and β), which are non-covalently bound.
 Functional integrins always have: one α subunit and one β subunit
 Both subunits contribute to ligand binding

9.  Ligand binding is divalent cation dependent (Ca ++ , Mg++ and Mn++)
 Common ligands are:
 the ECM proteins: fibronectin, vitronectin, collagen and laminin
(recognised by multiple integrins) or members of the Ig superfamily.
 Key integrin function: cell migration

10.  Integrins are key molecules during early development, having roles in
fertilization, gastrulation, implantation, placentation, nervous system
formation, myogenesis and blood vessel formation.
 Integrins also regulate extracellular matrix (ECM) assembly →proper
interactions of cells with ECM is critical for correct development

11. IgCAMs
 Ig-superfamily includes over 100 members many of
which are cell adhesion molecules. All have one or more
immunoglobulin (Ig)-like domain.
 IgCAMs recognise both homophilic and heterophilic
ligands.
 Ig-like domains are β-sheets stabilised by di-sulphide
bonding.

12.  The Selectins: There are three selectins-
 E-selectin, found exclusively on endothelia
 L-selectin, found on all circulating leukocytes, except activated T-
lymphocytes
 P-selectin, found in secretory granules of platelets
and endothelial cells.

13.  Selectins are noted for their role in white blood cell (leukocyte) migration
into the tissues during inflammation.
 Leukocyte migration is controlled by the interactions that occur between
the leukocyte and the vascular endothelia.
 L-selectin also functions outside of vasculature - role in embryo
implantation

14.  What makes an embryo stick? ….L-selectin does!!
 L-selectin initiates interactions of human blastocysts
with the uterine lining.