1. Cell to Cell Junctions and Adhesion
Lecture 24 BSCI 420/421 Oct 28/29, 2002
“In our every deliberation, we must consider the impact of our decisions on the next seven generations.”
- From the Great Law of the Iroquois Federation
A. Cell Adhesion Molecules
B. Cell-Cell Junctions
1. Occluding Jxs
2. Anchoring Jxs
3. Communicating Jxs

2. Formation of multicell organisms requires specific interaction
between cells to hold the cells together and to communicate
in order to coordinate activities.
A. 4 types of Cell Adhesion Molecules (CAMs)
are used to hold animal cells together:
Cadherins
Ig-like CAMs
Selectins
Integrins
All are single-pass transmembrane proteins anchored to the
cytoskeleton by their cytoplasmic domains.

3. Cadherins – Ca2+ binding adhering proteins
When Ca2+ is bound to the 5 cadherin-repeat domains,
They can bind to similar domains from an adjacent cell.
Removal of extracell Ca2+ can cause dissociation of cells.

4. Cadherin interactions are homophilic, with identical cadherens
interacting to form tissues of like cell types.
Table 19-3
Classical cadherins
E – epithelial & embryonic cells
P – placental & epidermis
N – Neural cells, lens, & muscles
VE – Vascular endothelial cells
Non-classical cadherins
Desmocollin and desmoglein – desmosomes of epithelia like skin
Protocadherins – synapses

5. Cadherins are liked to the actin cytoskeleton by catenins

6. 2. Ig-like CAMs
Are Ca2+ independent CAMs
20 different N-CAMs all by alternate splicing of one gene

7. 3. Selectins
Mediate transient interactions by heterophilic binding to cell
surface glycoproteins on other cells.

8. 4. Integrin
Binds cells to the extracellular matrix (fibronectin or laminin)
Or to Ig-family receptors. Binding can be regulated.

9. B. Cell to Cell Junctions are formed when groups of molecules
Interact between two cells.
3 broad classes:
Occluding Jxs 2. Anchoring junctions 3. Communicating jxs
“ “ seal cells together to prevent passage of
material between cells.
Main type: Tight Junctions
elect-dense
tracer to
Fig apical [ l ] or
basolateral [r]

10. TEM of Tight Jxs: Freeze-fracture & thin section views
Fig 19-4-pt2

12. Recall 2 important fxs of tight jxs
In glucose transport across
Int. epithelia:
1. Prevent flow of
Glucose between cells
2. Prevent lateral
diffusion of transporters
From one mem.
Domain to the
other

13. 2. Anchoring Jxs
a. Adherens Jxs

14. b. Desmosomes are circular spot junctions that produce strong
adhesions between two cells.
Esp. skin, intestinal epithelia, heart muscle Fig

15. Diagram of desmosomes Hemidesmosomes look like
½ des, but use integrins inst.
of cadherins

16. 3. Communicating Jxs
Gap Jxs allow small molecules to flow between cells: e.g.: Ions, sugars, NTs, cAMP
2 membranes are separated by a 2 nm gap.
Six proteins called connexins form a connexon and 2
connexons end to end form a 1.5 nm channel between 2 cells.
Fig 19-16

17. The size of the gap jxn channel was determined by
injecting fluorescent peptides of different sizes into
Gap jx-coupled salivary gland cells of Drosophila.
1200 Da mols could pass but 2000 Da mol would not.
Injection of Ca2+ along w peptides closed the channel.
Why would cells want to do this?

18. Fxs; Fig 19-17
Synchronizing beat
of heart muscle cells.
Coupling oocyte to
Granulosa cells
Mutant Cx37 causes
Infertility
Oocyte needs signals
from the receptors on
The granulosa cells
For ovulation.

19. Plasmadesmata serve similarly as comm. jxs in plants
Fig 19-20