What is cell signaling?
• Mechanisms that one cell uses to
communicate and influence the behavior of
another cell.
• In a broader sense, the signaling could include
environmental cues received by a cell
• Smell
• Light
• Mechanic pressure
• Heat
• A biological molecule
• Others
Three ways by which cells communicate with one anothe
Long or short ranch signaling by secreted molecules
Slow, less specific
But can signal to multiple cells
Signaling strength is distance-dependent
Contact signaling by plasma-membrane-bound molecules
Faster, very specific
But only affect a few cells
Contact signaling via GAP junctions
Very fast, very specific
Also affect a few cells
Three strategies of cell signaling by secreted molecules
1) Endocrine
Specialized endocrine cells secrete hormones,
which travel through the bloodstream to
target cells that are distributed widely
throughout the body.
2) Paracrine
Cells secrete local chemical mediators to affect
neighboring cells which usually are not the
same cells as the signaling cell. To become a
local mediator that acts only on cells in the
immediate environment, these molecules are
rapidly taken up by target cells, destroyed by
extra-cellular enzymes, or immobilized by
extra-cellular matrix.
3) Synaptic signaling
Nervous system. Cells secrete neurotransmitters at specialized junctions called chemical
synapses; the neurotransmitter diffuses across the synaptic cleft, typically a distance of about
50 nm, and acts only on the adjacent post-synaptic target cell.
Which of the followings has the faster
signaling speed?
A) Endocrine signaling
B) Synaptic signaling
C) Signaling by paracrine
D) All have similar speeds
Comparison of endocrine and synaptic signaling
Slow (minutes)
Specificity depend on ligands and receptors
Diluted in the blood
Very Fast
Precise
Not Diluted
The biochemistry of the cell signaling
• The nature of the signals
A. Environmental cues: light, chemicals, food
mechanical pressure, pheromones, and heat etc.
B. Cellular signals
chemicals (Ions), hormones, peptides, lipid,
growth factors, membrane bound ligand, and gas
(NO and CO).
- hydrophilic signals: can not diffuse into a cell
and signal by binding to cell surface receptor
- hydrophobic signals: carried by carrier protein
in the blood and enter cells
Receptors (the molecule that receives the signal)
1) Ion channel-linked receptors
2) G-protein-linked seven transmembrane receptors
3) Enzyme-linked receptors:
-receptor protein kinases: tyrosine kinases, serine/thronine kinases
-receptors coupled to protein kinases
-protein tyrosine phosphatase receptors
4) Intracellular Receptors—Steroid hormone receptors
Animal Development
Cleavage and Blastomere
In all animal species known so far, differentiation begins by a process called cleavage, a
series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into
numerous smaller, nucleated cells. These cleavage-stage cells are called blastomeres.
The C. elegans Cell Lineage
z yg ote
B
A
S
M
E
C
D
1090 cells are generated and 131 of them die
P
4
X
X
THE DECISION OF LIFE VS. DEATH
Proliferation
Signals
Differentiation
Death
What is the function of cell division or cleavage?
It generates different cells
How does cell division generate two different cells?
What is the function of cell division or cleavage?
It generates different cells
How does cell division generate two different cells?
Unequal distribution of
cytoplasmic determinants
A
B
Unequal cell division
A
Cell-cell interaction
B
A
B
Three different types of embryo development
1) Mosaic Development (autonomous specification):
determined by local determinants and no cell-cell
interaction
Experimental test?
remove one blastomere, the blastomere still develop as it
will be in the intact embryo
2) Regulative Development (conditional specificaiton):
determined by cell-cell interaction and local determinants
not important (e.g. mouse)
Experimental test: if remove one blastomere, the other
blastomere will take over and the embryo is fine.
3) Intermediate (Xenopus, fly and C. elegans)
local determinants and cell-cell interaction are
both important.
Cell-cell interaction affects cell fate determination
Intercellular long-range signaling (Wnt signalling in fly)
This signaling mode most likely is mediated by
A) Light
B) Gas
C) Membrane-bound proteins
D) Secreted factors
E) Lipid
Intercellular short-range signaling
This signaling mode most likely is mediated by
A) Ion
B) Gas
C) Membrane-bound proteins
D) Secreted factors
E) Sound
Intercellular relay signaling
Three different ways by which a target cell responds to a signal
Position (EMS and P2)
ABp
ABa
P2
EMS
Time
ABp
ABa
P2
EMS
Concentration (Morphogen)
Morphogen
D C B
A B C D