Download gastrulation - Instructure

Outline Questions
Understanding Gastrulation and Body Folding
•  Why do developing organisms need multiple cell layers?
•  What are the three tissue layers created by gastrulation?
•  How does gastrulation proceed in various vertebrate model
organisms (examples: amphibians and birds)?
•  What is an inducer, and why is this structure so important in
development?
•  What is body folding?
–  How is a three dimensional structure created?
–  How does this explain the tubular structure of many organisms?
Bio200
Gastrulation and Migration
Our Goals: Body Axes and
Multiple cell layers
•  Axis plan
–  Anterior/posterior
–  Dorsal/ventral
•  All tissues come from one
of:
–  Ectoderm
–  Mesoderm
–  Endoderm
•  Gastrulation is the process
of creating cell tissue layers
Our Goals: Body Axes and
Multiple cell layers
•  Axis plan
–  Anterior/posterior
–  Dorsal/ventral
•  All tissues come from one
of:
–  Ectoderm
–  Mesoderm
–  Endoderm
•  Gastrulation is the process
of creating cell tissue layers
Ectoderm-derived
Nervous system
Cornea and lens of eye
Epidermis of skin
Epithelial lining of:
mouth and rectum
Mesoderm-derived
Skeletal system
Circulatory system
Lymphatic system
Muscular system
Excretory system
Reproductive system
Dermis of skin
Lining of body cavity
Endoderm-derived
Epithelial lining of:
digestive tract
respiratory tract
reproductive tract
urinary tract
Liver
Pancreas
Thyroid
Parathyroids
Thymus
Gastrulation is amazing
Sea Urchin Gastrulation
http://www.youtube.com/watch?v=Lgb4wMsZwZA
Fruit Fly Gastrulation
http://www.youtube.com/watch?v=j87y7EAj8qE
Frog Gastrulation
http://www.youtube.com/watch?v=dXpAbezdOho
!"#$%&$"'&$()*$)('+,$"'-'.$/0#$$"'&$#($1
•  What is the structure at top left?
• !"2#('&+3'*'--&*+-+('45-)'7('47#,42'--+6/
Why
are *'--&
some
cells
red, blue
!"2
#(' &+3'
*+-+('4
5-)'colored
('4 #,4 2'--+6/
and yellow?
•  What do the arrows indicate?
Frog Gastrulation
Ectoderm
Mesoderm
Endoderm
Blastocoel
Dorsal lip
Cross section
Blastopore
Pre-Gastrulation
Whole embryo
1.  Regions of the frog blastula
contain cytoplasmic
determinants that determine
their fate during gastrulation.
Initial Gastrulation
Blastopore
2. Formation of the blastopore
opening in the embryo. Surface
cells move into the interior
through the blastopore.
Frog Gastrulation
Ectoderm
Mesoderm
Endoderm
Presumptive gut
Cross
section
Whole
embryo
3. The blastocoel shrinks as the
surface cells continue to move
inward, forming the three
embryonic tissue layers.
4. The three embryonic tissue
layers are formed, ready for
organogenesis. The blastopore
(future anus in frogs) surrounds
a plug of yolk cells.
http://www.mun.ca/biology/desmid/brian/BIOL3530/DEVO_03/ch03f12.jpg
Chicken Gastrulation:
Creating the Primitive Streak
Top view
Side view
A
Cell migration increases
density in the center
P
Single layer of embryonic
cells above a layer of
extraembryonic tissue
Primitive streak
The Henson s node
cell group (inducer)
forms at one end of the
primitive streak
If Hensen’s node from a quail embryo is transplanted
into a developing chicken embryo, a second embryo
begins to develop. What does this experiment imply?
Chicken Gastrulation:
Inducing Cell movement from A to P
Top view
Henson s node
sends out signal
to gastrulate
Side view
Signaled cells invade
into the embryo,
creating cell layers
Henson s node migrates posteriorly…
Inducer:
Cells that signal gastrulation
• 
A group of cells in developing
embryos that release the necessary
signals for gastrulation
• 
This function is
–  transferrable
–  At least partially conserved between
related species
Inducer:
Cells that signal gastrulation
• 
A group of cells in developing
embryos that release the necessary
signals for gastrulation
• 
This function is
–  transferrable
–  At least partially conserved between
related species
Body folding: Creating basic embryo morphology
• 
As development proceeds,
the body shape folds
anteriorly then posteriorly
• 
The embryo gradually loses
most contact points with
yolk
Top view
Side view
Body folding: Creating basic embryo morphology
• 
As development proceeds,
the body shape folds
anteriorly then posteriorly
• 
The embryo gradually loses
most contact points with
yolk
• 
Sustained by vasculature
(blood vessels)
• 
Apoptosis links endoderm
to outside in front and back
This creates the digestive
tract
• 
Top view
Side view
Gastrulation through Neurulation
http://www.youtube.com/watch?v=D76B0K-D4rY
Key Concepts
• 
Gastrulation is the process of creating three cell layers
–  These cell layers are ectoderm, mesoderm, and endoderm
–  Each cell layer is destined for a set of tissues in the body
• 
Gastrulation requires coordinated cell movements, signaling,
differentiation and proliferation to create cell layers.
–  Inducers are key signaling cells that influence surrounding tissues to
initiate tissue formation.
–  Different organisms have different patterns of gastrulation typified by
particular cell movements.
• 
Body folding creates a three dimensional shape from a flat
sheet of cells using cell movements and sometimes apoptosis to
arrive at a final shape.