Cadherins & Catenins, M. Sc. Zoology, Mumbai University.

Cadherins & Catenins, Developmental biology.

1. Cadherins & catenins THE GLUE THAT HOLDS LIFE TOGETHER

2. Cadherins : Cadherins – Calcium dependent adhesion mol. Def. – Cadherins are calcium-dependent cell adhesion molecules that bind to other cadherins of the same type ( homophilic )

3. Cell adhesion mol. (CAM): Proteins involved in cell-cell adhesion (sticking) They unite epithelial cells to form sheets & mesenchymal cells to form aggregates They separate different tissues from one another (sorting)

4. Structure of CAM: Polypeptides: 720-750 a.a . Components/Domains: Cytoplasmic/Intracellular Transmembrane Extracellular

5. Types of Cell adhesion molecules: Calcium independent: Immunoglobulin superfamily ( IgSF ) CAMs Lymphocyte homing receptors/ addressins Calcium dependent: Integrins Selectins Cadherins

6. Cytoskeleton: It is a framework of polymeric protein filaments inside the cells Provides stability to the cell Generates forces leading to changes in cell shape and cell movement Facilitates intracellular transport of organelles Communicates with extracellular matrix

7. Types of polymer in cytoskeleton: Microfilaments (Actin) Microtubules Intermediate filaments (keratin)

8. Microfilament/actin filaments: Polarized actin polymers found in cytoplasm of eukaryotes Arranged in bundles & lattices Provide strength & support Associates with myosin fibers to generate contractile fibers Which facilitate change in cell shape & movement Forms contractile ring during cytokinesis

9. Microtubules: Polarized structure comprising a circular arrangement of polymerized tubulin protofilaments found in cytoplasm Maintenance of axons, microvilli, cilia, etc. Mitotic spindle apparatus With the help of motor proteins (kinesis and dynein) they facilitate intracellular transport.

10. Intermediate filaments: Fulfil a structural role Ex: neurofilaments , keratin, etc. Polymers of 10nm. in diameter Possess a conserved α -helical structure It has a N-terminal & C-terminal

11. Bindings & interactions: Interactions: Cell-cell Cell-extracellular matrix Bindings: Heterophilic Homophilic

12. Coming back to cadherins : Functions: Establishing & maintaining intercellular connections Spatial segregation of cells Organization of animal form

13. Classification of cadherins : There are over 100 cadherins in vertebrates And fewer than 20 in invertebrates Four groups of cahderins : Classical Desmosomal Protocahderins Unconventional

14. Types of classical cadherins : E- cadherins (epithelial cadherin or uvomorulin or L-CAM) P- cadherins (placental cadherin) N-cadherin (neural cadherin) EP-cadherin/C-cadherin (frog blastula)

15. Catenins : ‘Catenin’ => Latin for chain Def. – family of proteins found in complex with cadherins of animal cells Types: α -catenin β -catenin γ -catenin 𝛿-catenin

16. Alpha catenin: Functions as a linking protein between cadherins & actin containing filaments of the cytoskeleton It has been reported that it can also bind with vinculin & α - actinin Regulates actin filament assembly Doesn’t have armadillo repeats

17. Beta catenin: Dual function protein: Regulates coordination of cell-cell adhesion and gene transcription Alterations in localizations & expression levels => cardiac diseases Mutation & overexpression => cancer In humans – CTNNB1 gene Homologous to γ -catenin

18. Delta catenin: Contains 10 armadillo repeats 𝛿-2-catenin is expressed in brain Types: 𝛿-1-catenin 𝛿-2-catenin

19. Gamma catenin/ plakoglobin : Humans: JUP gene Homologous to β -catenin Cytoplasmic component of desmosome and adherens junction in cardiac muscles

20. Adherens junction: Sticky junction where the transmembrane protein fibers adhere to each other in the extracellular matrix