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Cell-Cell Communication
In
Multicellular Organisms
Multicellular Organisms Require
Cell-Cell Interactions
Evolution of multicellularity
Volvox, an algae
Cell-Cell Adhesion Defines Multicellularity
The first traces of life appear nearly 3.5 billion years ago, in the
early Archaean. Clearly identifiable fossils remain rare until
the late Archaean, when stromatolites, layered mounds
produced by the growth of microbial mats, become common in
the rock record.
Caulobacter crescentus
More Complex
Multicellular
Organisms have
Specialized Cell
Types
Saccharomyces cerevisiae (G . Fink)
Cells Can Interact
With Each Other
Indirectly
Through
Protein-based
Scaffolds
Microbial Mats = Biofilms
Attachment of a bacterium to a surface, or substratum, is the
initial step in the formation of a biofilm
Cell-surface adhesins that mediate contact with the host matrix
The maturation of a biofilm community and their
architecture can vary from flat, homogenous biofilms,
to highly structured biofilms,
connection between quorum sensing and biofilm formation
Bacterial and fungal pathogens form biofilms
Microbial Mats = Biofilms
Hypothetical signal gradients in a biofilm system. This schematic represents a side-view of (a) a flat
and (b) a structured biofilm (s = substratum). This diagram represents speculation regarding potential
signal gradients (indicated by the gray scale), with higher signal concentrations indicated by darker
coloration. Factors, such as diffusion constants for the signal, mass transfer and non-uniform signal
production, within different regions of the biofilm could all affect signal gradients. The two
micrographs at the right of the figure represent side-views of confocal micrographs of P. aeruginosa
PAO1 forming a flat and a structured biofilm.
Quorum Sensing
Bacteria and Fungal Species Communicate
By Sending and Receiving Chemical Signals
the accumulation of signaling molecules enable a single cell to sense the number of bacteria (cell density).
The marine bioluminescent bacteria Vibrio fischeri was grown in liquid cultures and it was observed that
the cultures produced light only when large numbers of bacteria were present (Greenberg, 1997).
Quorum Sensing
An Australian pinecone fish (12
cm long). The red organ on the
lower jaw is a light organ that
contains 1010 V. fischeri cells
per
ml
fluid.
Australian
pinecone fish are nocturnal reef
dwellers and they use the light
organ to search for prey at
night.
A Hawaiian bobtail squid. This adult
squid is 2 cm long. There is a V.
fischeri light organ close to the ink
sac within the mantle cavity of the
animal. This light organ contains 1011
V. fischeri cells per ml. These
nocturnal squid emit light downwards
through the mantle cavity and, by
matching the intensity of the moonand starlight above, they become
invisible to predators below them.
Quorum Sensing
The lux operon contains luxI followed by five genes that are required for light production
(luxCDABE) and an additional gene of unknown function (luxG). The luxC, luxD and luxE genes
code for components of an acid reductase that converts the long-chain fatty acid tetradecanoic acid
into the fatty-aldehyde substrate (tetradecanal) for the light-producing enzyme luciferase. The luxA
and luxB genes encode subunits of luciferase. The luxI gene encodes the enzyme (autoinducer (AI)
acyl-homoserine lactone synthase) that produces the quorum-sensing signal 3-oxo-C6-HSL. The
single gene transcribed in the opposite direction, luxR, encodes the signal-responsive transcription
activator of the lux operon.
Quorum Sensing
Quorum Sensing
Model of acyl-homoserine-lactone (acyl-HSL) quorum sensing in a bacterial cell. Tentative
mechanisms for acyl-HSL synthesis and acyl-HSL interaction with LuxR-type proteins are shown. Double
arrows with filled yellow circles at the cell envelope indicate the potential two-way diffusion of acyl-HSLs
into and out of the cell. The proposed dimerization of LuxR (red) is based on genetic evidence and
biochemical analysis of TraR; other LuxR-type proteins might form higher-order multimers.
All C.elegans cells Are Formed in a Defined
Program (959 somatic)
Cells Stick Together by Tight Junctions
Prevent Membrane
Protein and Lipid
Diffusion
Desmosomes Are Button-Like Points of Intercellular
Contact that Rivet Cells Together
GAP Junctions
Examples of Cell Adhesion Molecules
30nM
Integrins are Matrix Receptors
Bind ligand with low affinity
More of them on the cell surface
Allowing Cell Separation from the Matrix
8 integrins bind fibronectin
Inside-out signaling
focal adhesion kinase (FAK) in mediates signals from the
extracellular matrix through integrin receptors.
FAK and its interacting partners play a central role in propagating
signals that regulate cell motility.
Non-adherent cells undergo programmed cell death: Apoptosis
-double stranded DNA cleavage
1-2 breaks can cause a cell cycle checkpoint
-asymmetry lost in PM
Phosphatidyl serine becomes exposed to WBC
-caspase production
Proteases that are themselves activated by cleavage
Proteolytic cascade
-pores in the mitochondria
Involved in procaspase activation
Growth Factors and DNA damage can cause apoptosis
Bloom and Cross Nature Reviews Molecular Cell Biology 8, 149–160 (February 2007) | doi:10.1038/nrm2105