Gastrulation Flashcards
Morphogenesis 3 movements
- Internalization
- invagination/involution
- ingression - Convergence and Extension
- mediolateral intercalation
- directed migration - Epiboly
- radial intercalation
- cell shape changes
How do differentiated cells move and reorganize during development to generate the body plan and a functional organism?
Through morphogenesis
is the point in embryogenesis where the basic organization of the organism is established.
Gastrulation
Events in gastrulation:
- Establishment of the three basic germ layers;
- Groups of cells that will give rise to specific organ systems and tissues are moved into the right position;
- Groups of cells that will influence each other’s differentiation are positioned so they can have an effect on each other.
2-Fold Process in Amniotes:
Primary Gastrulation
Secondary Gastrulation
is the point in embryogenesis where there are MORPHOGENETIC MOVEMENTS
Gastrulation
Gastrulation changes:
- Cell shape
- Cell adhesion
Contraction of the ________ drives apical constriction
adhesion belt
Cytoskeletal events drive CELL SHAPE changes
Microtubules elongate, causing cells to become columnar -> Apical actin-filament bundles contract, narrowing the cells at their apices
A transcription factor that represses E-cadherin, a protein crucial for cell-cell adhesion.
Snail
E-Cadherin & Epithelial-Mesenchymal Transformation
Columnar epithelial cells = E-Cadherin -> Bottle cell = Loss of E-Cadherin -> Mesenchyme cell = No E-Cadherin
is a gradual, multifactorial process in which different cellular requirements can be independently regulated.
epithelial-mesenchymal transition (EMT)
4 Evolutionary Conserved Morphogenetic Movements in Gastrulation
- Emboly (internalization)
- Epiboly
- Convergence
- Extension
Emboly (internalization)
The first process in gastrulation.
* Invagination
* Involution
* Ingression/Delamination
“a form of cell spreading in which cells flatten out to cover a much larger surface area”
Epiboly
Local inward buckling of an epithelium
Invagination
Inward movement of a cell layer around a point or edge
Involution
Movement of individual cells or small groups from an epithelium into a cavity
Ingression
Splitting layers of cells (coordinated ingression)
Delamination
Spread of an outside cell layer (as a unit) to envelop a yolk mass or deeper layer
Epiboly
Movement of individual cells over other cells or matrix
Migration
Elongates the nascent germ layers from head to tail and narrows them from back to belly
Convergence & Extension
Summary of body axis elongation and driving mechanisms
Tissue level
Convergent extension
Inter-tissue flow
Intra-tissue flow
Growth
Swelling
Cell level
Intercalation
Specification
Movement
Proliferation
Differentiation
Gastrulation in Drosophila
Mesoderm morphogen
Endoderm morphogen
Spatzle
Trunk
Gastrulation in Sea urchin:
- Primary Mesenchyme cells (PMCs) ingress (driven by changes in cell adhesion)
1a.Invaginating PMCs migrate on the extracellular matrix lining the blastocoel using filopodia
1b. PMCs eventually fuse and form the spicules (skeletal rods) - Apical constriction and changes in the extracellular matrix create a dome-shaped invagination (archenteron)
- Cell intercalation (convergent extension) converts the dome (archenteron) into an elongated tube
- Secondary mesenchyme cells (SMCs) at the leading edge of the gut tube use filopodia to look for cues at the animal pole and pull themselves to that site
Changes in cell adhesion drive the first step of gastrulation
Xenopus laevis embryo
Ectoderm
Neuro-ectoderm
Dorsal mesoderm
Ventral mesoderm
Spemann’s organizer
Nieuwkoop centre
Blastocoel prevents cells from interacting too soon and allows space for cell migration
Gastrulation in Frog:
Apical Constriction of _______ drives blastopore invagination
bottle cells
Gastrulation in Frog:
1. Blastopore formation
2. Involution of Marginal Zone Cells
➢ movement of inside MZ cells dependent on ectoderm cells of blastocoel roof secreting fibronectin
3. Formation of the Archenteron = Convergent extension of dorsal mesoderm
4. Epiboly of ectoderm
is essential for mesodermal cell involution during gastrulation
Fibronectin
Gastrulation in Chick:
1. Appearance of primitive streak
- Formation of 2-layered blastoderm
- Ingression of epiblast cells in to subgerminal space
- Migration of marginal zone cells to form hypoblast
- Epiboly of ectoderm –yolk becomes enclosed by ectoderm
Cells passing __________ form the head structure
Hensen’s node
Gastrulation in Mammals
- begins at the posterior end of the embryo
- _______control cell migration and specification -–downregulate E-cadherin; regulate ______, ______ and _______ (genes that influence specification)
FGFs; snail; Brachury; Tbx6
Time line of early human development
Fertilization -> Cleavage (1 day) -> Blastocyst (6 days) -> Implantation -> (14 days) -> Gastrulation begins (17 days) -> Neurulation begins (22 days) -> Gastrulation complete (23 days) -> Neurulation complete & Differentiation begins (>24 days)
Human Gastrulation:
Formation of Epiblast and Hypoblast (ICM)
Delamination occurs prior to implantation
Human Gastrulation: Tissue Formation
Cells entering the node become
notochord
Human Gastrulation: Tissue Formation
1st cells entering primitive streak become
endoderm
Human Gastrulation: Tissue Formation
Later cells entering primitive streak become
mesoderm
Human Gastrulation: Tissue Formation
Cells that don’t enter the primitive streak become
ectoderm
Differentiation of Primary Germ Layers (from the gastrula)
Ectoderm
- Nervous system
- Epidermis of skin
Mesoderm
- Skeleton
- Muscles
- Circulatory system
- Gonads
Endoderm
- Digestive tract
- Respiratory system
- Liver, pancreas, bladder
Human disorders attributed to abnormal gastrulation
Conjoined twinning
Chordoma
Caudal agenesis
Do plants undergo GASTRULATION?
No
Plants, like animals, develop 3 basic tissue systems (_____, ________, and _______), but do not rely on gastrulation to establish this layered system of tissues.
dermal; ground; vascular
“It is not birth, marriage or death but GASTRULATION, which is truly the most important time in your life.”
- Lewis Wolpert (1986)
