Cell-Cell
Communication
Induction and Competence
Induction
•
When one group of cells
changes the behavior of an adjacent set of cells
•
They may change their
shape, mitotic rate or fate
•
Two components of
induction
•
1. Inducer - the tissue
that produces a signal or signals that change the cellular behavior of the
other tissue
•
2. Responder - the
tissue being induced
Competence
•
Ability to respond to a
specific inductive signal - acquired condition
Ectodermal
Competence
Induction
by Pax6
•
Pax6 protein important in making
the ectoderm competent to inductive signal from the optic vesicle
Pax6
as a Competence Factor
• Recombination Experiments
Reciprocal
Inductions
•
In this situation the
inducer becomes the induced
•
Ex. - The lens is
normally induced by the optic vesicle
•
Now under the influence
of factors secreted by the lens - the optic vesicle becomes the optic cup
•
The wall of the optic
cup differentiates into two layers, pigmented retina and neural retina
•
The lens is also
inducing ectoderm to become the cornea (remember to respond it has achieved a particular competence
to respond to the inductive signals from the lens
Induction
of Mouse Lens
Summary
of Inductive Interactions
Instructive
Interactions
•
Signal from inducing
cell is necessary for initiating new gene expression in the responding cell
(e.g. optic vesicle - placed under new region of ectoderm - that region now
forms a lens - instructive interaction)
Principles
of Instructive Interactions
• Wessel (1977)
• 1. In the presence of tissue A, responding tissue B
develops in a certain way
• 2. In the absence of tissue A, responding tissue B
does not develop in that way
• 3. In the absence of tissue A, but in the presence of
tissue C, tissue B does not develop in that way
Permissive
Interaction
•
The responding tissue
contains all the potentials that are to be expressed, and needs only an
environment that allows the expression of the traits
•
E.g. a tissue may need a
solid substrate containing fibronectin or laminin to develop
Epithelial-Mesenchymal
Interactions
•
Epithelial tissue
- sheets of tubes of cells from any germ layer
•
Mesenchymal cells
- loosely packed, unconnected cells - derived from mesoderm or neural crest
•
All organs have an
epithelium & associated mesenchyme
Epithelial-Mesenchymal
Interactions
•
Regional specificity of
induction
•
Chick epidermis signals
the underlying dermal cells (from mesenchyme) to from condensations -
the condensed dermal mesenchyme responds by secreting regionally specific
cutaneous structures like broad feathers on the wing, narrow ones on the thigh
and scales and claws of the feet
•
Mesenchyme plays
an Instructive role
Regional
Specificity of Induction
Genetic
Specificity of Induction
•
Epithelium responds to
the mesenchyme cell signal - can only do so as far as its genome permits
•
Discovered by transplantation
experiments
•
The instructions of
mesenchymal tissue can cross species barriers
•
However the response
of the epithelium is species-specific
Genetic
Specificity of Induction