Gastrulation
Gastrulation - The point in embryogenesis where the
basic organization of the organism is established.
A. Establishment of the three basic germ
layers
Ectoderm, Mesoderm, Endoderm
B. Groups of cells that will give rise to
specific organ systems and tissues
are moved into the right position both
externally and internally.
C. Groups of cells that will influence each
others differentiation are positioned so
they can have an effect on each other.
QUESTIONS?
How are layers of tissue established?
How do cells get to their proper positions for development?
In part, this is accomplished by
various types of Morphogenetic
Movements.
Morphogenetic Movements
Epiboly
Morphogenetic Movements
Invagination, Evagination
Morphogenetic Movements
Involution
Epiboly over a fold
Involution
Morphogenetic Movements
Delamination
Morphogenetic Movements
Ingression
Morphogenetic Movements
Cell Migration
Cell Migration
Morphogenetic
Movements
“Intercalation: rows of cells move between one another,
creating an array of cells that is longer (in one or more
dimensions) but thinner.”
“Convergent Extension: rows of cells intercalate, but the
intercalation is highly directional.” - involved in formation of
the primitive streak in avian and mammalian embryos.
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html
Morphogenetic Movements
Differential Growth
.. ..
.. ..
time
.... .. ..
... .. ..
..
..
..
..
Starfish/Sea urchin gastrulation
http://www.gastrulation.org/
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation1.html
http://www.luc.edu/depts/biology/dev/urchgast.htm
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html
ingression - primary and secondary mesenchyme
invagination - initial formation of the archenteron
convergent extension - lengthening of the archenteron
Amphibian Gastrulation
(Urodeles, e.g. salamanders)
Urodele blastula
Urodele
18 - 20 hr
Urodele
18 - 20 hr
Urodele
18 - 20 hr
28 hr
38 hr
http://biology.kenyon.edu/courses/biol07/gastmovs.html
15 hr of time lapse, 48 min/sec http://www.gastrulation.org/
Shell
Shell membrane
Thin albumin
Blastodisk
Yolk
Chalazae
Air pocket
http://www.zoomwhales.com/subjects/birds/label/chickenegg/
The morphogenetic movement
that results in elongation of the
primitive streak is convergent
extension.
z
Chicken (Avian) Gastrulation
Formation of the primitive streak
Morphogenetic movement involved in
the formation of the primitive streak is
convergent extension.
PRIMITIVE STREAK
Actually, this is a human embryo. We have the
same type of gastrulation as a chicken embryo,
yet we do not have a large yolky egg.
Why might this be?
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14A.html
Establishing the Endoderm
Extraembryonic endoderm
Primary Hypoblast
Secondary Hypoblast
Embryonic endoderm
Derived from cells that are
originally in the epiblast that
ingress through the primitive
streak region and then
migrate and insert into the
hypoblast layer.
Chicken (Avian) Gastrulation - primary and secondary hypoblast
Chicken (Avian) Gastrulation
Fate map as gastrulation is beginning
Yolk
Yolk
Yolk
Yolk
Ingression during avian gastrulation
Two regions of ingression:
1. Hensen’s Node
2. Primitive groove
Timing (waves) of ingression:
Later,
Hensen’s node - initial waves
1st wave - foregut endoderm (mostly as primitive
streak forms)
2nd wave - head mesoderm
3rd wave - chordamesoderm
* Hensen’s node will contribute
to somites as well
*Some cells from Hensen’s
node will remain in the
epiblast and contribute to
neural plate
Ingression during avian gastrulation
rimitive groove
st wave - rest of embryonic endoderm (mostly as primitive streak forms)
nd wave - mesoderm
(embryonic & extraembryonic)
Chicken (Avian) Gastrulation
Chicken (Avian) Gastrulation
groove
Embryonic
ectoderm
embryonic endoderm
Chicken (Avian) Gastrulation - embryonic endoderm
Chicken (Avian) Gastrulation
Establishment of the primary germ layers
Chicken (Avian) Gastrulation
See animation on digital lab
manual
Chicken (Avian) Gastrulation