22 - Cell Cell Communication

four issues addressed by the cytoskeleton

1. maintain shape

2. move the cell around

3. move cargo inside - cell transport

4. combine all of this to divide

5. enable cell-cell and cell-ECM interactions

cytoskeleton - a cells structure

• microtubules (tubulin)

• intermediate filaments

• microfilaments (actin)

microfilaments are made of

actin and are the smallest

microtubules are made of

tubuline and are the largest

intermediate filaments

more vairable in composition (keratin or vimentin) and there aren’t tracks and mainly provide structure

organization of epithelial cell layer

difference in shape of layer among organs but common features

there are different organizations

how are epithelial cells different from polarized neurons

epithelial cells are polarized - they have a clear directionality

polarized epithelial cells interact with what

interact with external surface, themselves, and the ECM (basal lamina)

(A)pical to (B)asal

Apical is the apex

basal is the base

what are synaptic celfts

not junctions, no physical connections here

tiny gap between two neurons at a synapse where a signal is transmitted, typically through the release of neurotransmitters

common features for cell junctions

cytoskeletal filaments (intermediate or microfilament)

adaptor proteins (part of ECM)

adhesion proteins

major components of ECM

proteoglycans - hydration, cushioning

elastin - elastic recoil

collagen - tension

fibronectin - cell adhesionelasy

elastins are as simple as their name

elastic

allow the ECM to stretch

prevents mechanical stress

what is collagen

formation of collagen fibers in connective tissue

collagen provides resistance for tensile force

what is fibronectin

interaction bt ECM and cells

cells bind to collagen through adaptor protein fibronection and integrin

primary adhesion proteins

integrin and cadherin

where are integrins integrated

integrate cells into the ECM

what are cadherins

calcium dependent adhesion super family proteins

calcium binding cadherin induced its conformational change that allows cadherin to bind each other

what determines cadherin binding partner

type and amount

direct contact with the cytoskeleton

often for anchoring or distributing stress

microfilament junctions

• anchoring junctions

• focal adhesion

intermediate filament junctions

• desmosomes

• hemidesmosomes

control molecular traffic between cells

coordinating junctions

• tight junctions

• gap junctions

ecm proteins

microfilament junctions

use actin for shape, tension, and communication

adherens junctions

connection: cell to cell

major proteins: cadherin

coordinate shape change and structure: form belts of cells that allow them to synchronize changes

mechanosensors: help cells detect and response to tension

focal adhesions

connection: cell to ECM

major proteins: integrins

sense mechanical and environmental cues: can transmit these senses into biochemical pathways

wound healing

focal adhesinos and wound healing

upon receving a wound, epithelial cells must migrate to heal

focal adhesins as anchors to keep cell in place as actin pushes cell forward

old focal adhesions dissociate as new ones are made → crawling

intermediate filament junctins

provide more mechanical resilience under stress

physically larger scaffold - stronger connections

desmosome and hemidesmosomes provide base of intermediate filament network

provide physical stength to epithelial cells

linking cells..bundles

linking cells bundles of intermediate filaments are via the desmosome

desmosomes

connection: cell to cell

major proteins: cadherins (desmoglein, desmocollin)

distribute mechanical stress: desmosome provide major mechanical support

these connections spread stress over multiple cells

desmosomes: cell/cell junction mediated by non canonical cadherin

the still require calcium, but unike E-cadherins in adheren junctions, they bind to intermediate filaments

desmoglein and desmocollin

what is an organ with major synchronized and constant contraction

the heart

hemidesmosomes

connection: cell to ECM

major proteins: integrins

very similar to desmosomes, but ECM

stabilize epithelial cells to ECM: strong connection to basal lamina

help organize polarity: strong connection forces cell in a specific orientation

tight junctions

connection: cell to cell

major proteins: cadherins (caudlins, occulidins) (similar non canonical proteins)

physical barrier: create a physical barrier preventing apical from basal → crucial in the gut and blood brain barrier

fence structues: by sealing the membrane, they prevent flow of membrane proteins

what does tight junction seal

sealing epithelial cell layer to separate basal environment from apical environment

claudin and occludin (belong to cadherin family proteins) form the tight junction

what are fences

tight junction prevent lipid movement (lateral diffusion of lipids) by sealing plasma membrane

gap junctions

connection: cell to cell

major proteins: connexins

directly send ions and small molecules

coupling of processes: this allows electrical coupling (syncing) together

synchronization: cells can act as a coordinated network due to coupling

what connects cells at gap junctions

the connexon complex

two connexons in register forming open channel bt adjacent cells

limitation of the size of molecules that GAP junction can pass through

“second messengers”

neighboring cells that receive that second messenger signal even if it didn’t come from their receptor

now a signal can be amplified and duplicated

what kind of process do you really want to be synchronized across cells

cell cycle and cell signlaing

cell junctions are varied

structural vs signaling

cytoskeleton is key for what

several connections

as in the gut, a cell can have many types of junctions

think locally as to what each can do for a cell