Transcript CHAPTER 7

Interaction of Cells with Other
Cells (5)
• Cadherins –
glycoproteins that
mediate Ca2+dependent cell-cell
adhesion.
Interaction of Cells with Other
Cells (6)
• Cadherins (continued)
– Also involved in transmitting signals from the
ECM to the cytoplasm.
– Mediate many of the changes in adhesive
contacts during embryonic development by
forming epithelial-mesenchymal transition
(EMT).
Cadherins and the EMT
Cadherins and the EMT
Interaction of Cells with Other
Cells (8)
• Adherens Junctions and Desmosomes:
Anchoring Cells to Other Cells
– Adherens junctions – they form “belts” near
apical surface called junctional complex.
– Cells of an adherens junction held together by
calcium-dependent linkages.
Intercellular junction complex
Intercellular junction complex
Molecular architecture of adherens junction
Interaction of Cells with Other
Cells (9)
• Desmosomes – disk-shaped adhesive
junctions between cells.
– Found in a variety of tissues.
– Contain cadherins that link the two cells
across a narrow gap.
– Cadherins of desmososme shave different
domain structures: desmogelins and
desmocollins.
Structure of a desmosome
Interaction of Cells with Other
Cells (10)
• The Role of Cell-Adhesion Receptors in
Transmembrane Signaling
– The transfer of information across the plasma
membrane is transmembrane signaling.
– Integrins and cadherins can transmit signals
from the extracellular environment to the
cytoplasm.
Interactions involving the cell surface
Interaction of Cells with Other
Cells (11)
• The binding of an
integrin with its
ligand can induce a
responses such as
changes in growth
potential.
The Human Perspective: The Role of Cell
Adhesion in Inflammation and Metastasis (1)
• Inflammation is a response to infection or
injury but can be triggered inappropriately.
• Inflammatory response:
– Recruitment of leukocytes to site of injury.
– Neutrophils attach to P- and E-selectins.
– Neutrophils start to “roll” along wall of vessel.
Movement of neutrophils during
inflammation
The Human Perspective: The Role of Cell
Adhesion in Inflammation and Metastasis (2)
• As neutrophils interact with inflamed
venule endothelium, platelet activating
factor (PAF) is displayed.
• PAF sends a signal to increase the binding
activity of some integrins.
• Activated integrins cause neutrophils to
stop rolling and adhere firmly to wall of
vessel.
The Human Perspective: The Role of Cell
Adhesion in Inflammation and Metastasis (3)
• Cancer is the result of abnormal cell
proliferation.
• The spread of a tumor to other parts of the
body is called metastasis.
• Metastatic cells have special cell adhesion
properties:
– Are less adhesive.
– Are able to penetrate several barriers.
– Are able to invade normal tissues.
Steps leading to metastatic spread
The Human Perspective: The Role of Cell
Adhesion in Inflammation and Metastasis (4)
• During growth and development of a tumor
there is loss of E-cadherin leading to less
adhesion.
• Changes in the numbers and types of celladhesion molecules lead to promote
metastasis.
7.4 Tight Junctions: Sealing the
Extracellular Space (1)
• Tight junctions (TJs) – specialized
contacts between epithelial cells.
– Located at the very apical end of the
junctional complex between adjacent cells.
– TJs serve as a barrier to the free diffusion of
water and solutes from the extracellular
compartment.
– Some TJs are permeable to specific ions or
solutes.
Tight junctions
Tight junctions
Tight Junctions: Sealing the
Extracellular Space (2)
• Occludins are
proteins found in
TJs.
• Claudins form the
major structural
component of TJs,
and may account for
selective differences
in TJ permeability.
• TJs form the bloodbrain barrier.
7.5 Gap Junctions and Plasmodesmata:
Mediating Intercellular Communication (1)
• Gap junctions – sites between animal
cells for intercellular communication.
– Composed entirely of membrane protein
connexin.
– Connexins are organized into a complex
called connexon.
Gap junctions
Gap junctions
Gap Junctions and Plasmodesmata:
Mediating Intercellular Communication (2)
• Gap-junction intercellular communication
(GJIC) allows the passage of low-weight
molecules.
• Gap junctions can allow integration of
activities of individual cells into a functional
unit.
• Compatibility differences between
connexins either promote or prevent
communication between different cells.
Passage of low-molecular-weight solutes
through gap junctions
Gap Junctions and Plasmodesmata:
Mediating Intercellular Communication (3)
• A new type of
communication has
been discovered –
tunneling nanotubes.
– It has been observed
in cells growing in
culture.
Gap Junctions and Plasmodesmata:
Mediating Intercellular Communication (4)
• Plasmodesmata are cytoplasmic
channels passing through cell walls of
adjacent plant cells.
– Are lined by plasma membrane.
– Contain a central structure, the desmotubule.
– Serve as sites of cell-cell communication.
Plasmodesmata
7.6 Cell Walls (1)
• Cell walls provide plants protection
against mechanical abrasion, pathogens,
and osmotic stress.
– The fibrous component is cellulose.
– Cellulose is organized into microfibrils,
which provide rigidity to the cell wall.
The plant cell wall
Cell Walls (2)
• The matrix of the cell wall contains
hemicelluloses, pectins, and proteins.
• Cell walls arise as a cell plate that forms
between the plasma membranes of newly
formed daughter cells.
• The walls of growing cells are primary
walls and allow flexibility lacking in the
thicker secondary walls of mature cells.
Synthesis of a plant cell wall