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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.
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.
QUESTIONS?
Morphogenetic Movements
Epiboly
Morphogenetic MovementsInvagination, Evagination
Involution
Morphogenetic Movements
Epiboly over a fold
Involution
Morphogenetic Movements
Delamination
Morphogenetic Movements
Ingression
Morphogenetic Movements
Cell Migration
Cell Migration
Morphogenetic Movements
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html
“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.
Differential Growth
Morphogenetic Movements
time
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.. ... .. .
.. .... . .. ......
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http://www.gastrulation.org/ingression - primary and secondary mesenchymeinvagination - initial formation of the archenteronconvergent extension - lengthening of the archenteron
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14.html
Starfish/Sea urchin gastrulation
http://www.luc.edu/depts/biology/dev/urchgast.htm
http://www.uoguelph.ca/zoology/devobio/210labs/gastrulation1.html
Amphibian Gastrulation(Urodeles, e.g. salamanders)
Urodele blastula
18 - 20 hr
Urodele
18 - 20 hr
Urodele
18 - 20 hr
Urodele
28 hr
38 hr
http://biology.kenyon.edu/courses/biol07/gastmovs.html
http://www.zoomwhales.com/subjects/birds/label/chickenegg/
Shell
Blastodisk
Chalazae
Thin albumin
Yolk
Air pocket
Shell membrane
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.
http://biology.kenyon.edu/courses/biol114/Chap14/Chapter_14A.html
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?
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
Yolk Yolk
Yolk Yolk
Chicken (Avian) Gastrulation Fate map as gastrulation is beginning
Yolk Yolk
Yolk Yolk
Ingression during avian gastrulation
1. Hensen’s Node
2. Primitive groove
Two regions of ingression:
2nd wave - head mesoderm
3rd wave - chordamesoderm
Later,
* 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
Timing (waves) of ingression:
Hensen’s node - initial waves1st wave - foregut endoderm (mostly as primitive
streak forms)
Primitive groove
1st wave - rest of embryonic endoderm (mostly as primitive streak forms)
2nd wave - mesoderm
(embryonic & extraembryonic)
Ingression during avian gastrulation
Chicken (Avian) Gastrulation
embryonic endoderm
grooveEmbryonicectoderm
Chicken (Avian) Gastrulation
Chicken (Avian) Gastrulation - embryonic endoderm
Chicken (Avian) GastrulationEstablishment of the primary germ layers
Chicken (Avian) Gastrulation
See animation on digital lab manual
Chicken (Avian) Gastrulation
