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Cell / Cell Interactions
Morphogenesis –
Development of functional anatomy
Cell communication
Pattern formation
& integrated activity
Cleavage
Cell / Cell Interactions
Morphogenesis –
Development of functional anatomy
Cell communication
Pattern formation
& integrated activity
 Chemotaxis
 Haptotaxis
 Galvanotaxis
Disruption of the tryptophan gradient around live eggs prevents navigation
Free amino acid
L-tryptophan –
directed chemotaxis
Requires
a natural
gradient
Selectively digests
tryptophan as it is
secreted
Elimination of
chemical gradient
Tryosine control for
effects of elevating
[aromatic amino acids]
- Red abalone Riffell, J. A. et al. J Exp Biol 2002;205:1439-1450
Chemotaxis
vs.
Haptotaxis ?
Development of the Pronephric duct
Galvanotaxis
Ca++
+++
Ca++ ++Ca++
Ca
--- Ca++
Differential cell adhesion
Townes & Holtfreter - 1955
- place cells in alkaline solutions or Ca++- or Mg++- free medium
to disassociate them
- mix cells together
- reaggregation
Fig. 3.23, pg. 68
Steinberg Thermodynamic Differential Cell Adhesion Model
Fig. 3.24, pg. 69
Themodynamic Model of Cell Interaction
Differential
cell adhesion
Fig. 3.27, pg. 72
Wrist
Knee
Mid-thigh
Fig. 18.24a, pg. 579
Monoclonal Ab
to isolate protein
for determination
of gene
Tripeptide binding sequence
Homophilic binding
Protease
cleaves
Talin;
binding/
uncoupling
with actin
Integrins - Binding to
extracellular matrix
Cadherins – Ca++ dependent
Fig. 3.28, pg. 72
Fig. 6.32, pg. 166
Induction
 Primary embryonic induction –
specific to events associated with
gastrulation in amphibians
 Secondary tissue induction –
permissive vs. instructive
Induction vs. Determination
1 – tissue capable
of inducing a
stimulus
Y
Inductive Event:
= cell surface receptors
= intracellular signaling
pathway
O = target genes
2 – tissue competent
of responding to
stimulus
Cells may gain competence
by repressing the activity of
an inhibitor
Gonad Development and Primary Sex Determination
Primary Induction
Presumptive
Ectoderm
Presumptive
Endoderm
Gastrulation in Amphibians
Fig. 10.7, pg. 296
Fig. 10.19, pg. 306
“Organizer” and Mesoderm Induction
Low [Xnr]
have high
[BMP-4 &
Xwnt-8]
Presumptive Ectoderm
High [Xnrs]
activate other
genes creating
Organizer region
Presumptive Endoderm
Xnr protein
concentration
Synergistic
Fig. 10.26, pg. 312
1 – tissue capable
of inducing a
stimulus
2 – tissue competent
of responding to
stimulus
Y
Inductive Event:
= cell surface receptors
= intracellular signaling
pathway
O = target genes
Head
Archenteron roof
Tail
Tail
Gastrulation in Amphibians
Fig. 10.7E, pg. 296
Regional Specificity of Induction
Fig. 10.34, pg. 318
Mesodermal
origin
Ectodermal
origin
Fig. 6.7, pg. 145
Thigh mesoderm
under wing
ectoderm
Leg mesoderm
under chest
ectoderm
Ankle mesoderm
under thigh
ectoderm
Regionally specific
mesodermal induction
of ectoderm
Genetic Specificity of Induction
Oral
ectoderm
Newt
Frog
Fig. 6.8, pg. 145
Area of presumptive
oral ectoderm
Mouse embryo
Chick embryo
2
3
1 – chick presumptive corneal epithelium + chick skin mesoderm
2 – chick presumptive corneal epithelium + mouse skin mesoderm
3 – chick jaw epithelium + D16 mouse jaw mesoderm
1
“Hen’s Tooth”
“The Development of Archosaurian
First-Generation Teeth in a Chicken
Mutant”
Matthew P. Harris, Sean M. Hasso, Mark W.J.
Ferguson, and John F. Fallon
21 February 2006, Volume 16, Issue 4, Pages 371-377
A and D
Alligator embryo
B and E
ta2 chicken mutant
Mutant
Wild-type sibling
- Talpid2 chicken mutant (autosomal
recessive mutation which affects
development of many organ systems);
- Don’t survive past embryonic stage;
Wild - type
Boundary
signaling
center
ta2 mutant
Frontonasal
process
Ect.
Oral
cavity
Mes.
Competent
mesenchymal
tooth cells
Ect.
Mes.
Gene expression during early development is shifted along the oral/aboral
boundary in ta2 mutants to redefine this boundary;
*** Both avian ectoderm and mesenchyme have potential to participate in tooth
development;
Developmental repositioning of epithelium with signaling potential so that it
overlies mesenchyme which is competent to form teeth.
Review Induction
Inductive signal
Competency
Obtained
New
Receptor
Pool
Repression
of Inhibition
Response
Differentiation
Lose competence
to 1st inductive
signal / gain
competence to
new inductive
signal
(Spemann 1901)
“Double-Assurance” hypothesis
Fig. 6.1, pg. 140
Lens Induction in Amphibians
Fig. 6.4a, pg. 142
Fig. 6.4b, pg. 142
Competence / Bias / Determination
Fig. 6.5a, pg. 143
“Presumptive cells”
Mark individual cell
with vital dye
Becomes brain cell
thus“presumptive
neural ectoderm”
Fig. 6.4b, pg. 142
Competence / Bias / Determination
Fig. 6.5a, pg. 143
Corneal Development