1
Q
Most distinguishing feature of early gastrula is the formation of the
A
dorsal lip of blastopore
2
Q
“Gaster” means
A
stomach
2
Q
GASTRULATION effects
A
Laying down the primitive gut
Cell movements and rearrangements (morphogenetic movements)
Starting to acquire positional information
Forming the three germ layers:
Ectoderm – outermost
Endoderm – innermost
Mesoderm – middle
3
Q
the three germ layers:
A
Ectoderm – outermost
Endoderm – innermost
Mesoderm – middle
3
Q
The precursor of the digestive gut marked by the formation of a
A
blastopore
4
Q
The Three Germ Layers
Epithelial type
Flat sheet; closely-packed; little amount of ECM
A
Ectoderm
Endoderm
4
Q
Prelude to morphogenesis (gradually generating the overall body plan)
A
morphogenetic movements
4
Q
The Three Germ Layers
Mesenchymal type
Loosely-arranged; plenty of ECM
A
Mesoderm
5
Q
molecular cues that will tell an embryonic cell where it is relative to the body axis
A
Positional Information
6
Q
The Three Germ Layers
Behavior:
Spread
Roll
Fold
Buckle
Bend
A
Ectoderm
Endoderm
7
Q
The Three Germ Layers
Behavior:
Migrate
Intercalate
ingress
A
Mesoderm
7
Q
Allows behaviors to occur in various combinations
is the process by which epithelial cells — which are tightly connected, stationary, and organized in layers — transform into mesenchymal cells, which are motile, less adhesive, and able to migrate through tissues.
A
Epithelial-mesenchymal transition
8
Q
What type of tissue is this?
Can undertake major morphogenetic movements
1. Invagination
2. Epiboly
3. Involution
4. Convergent extension
5. Delamination
6. Passive movement
A
Epithelial Type
8
Q
samples were Mesenchymal Type and Epithelial Type Occur in various combinations
A
Change in the rate of cell division causes cells to spread out (epiboly)
Involution requires mass movement of cells (migration)
9
Q
What type of tissue is this?
Can undertake changes in cell behaviors/activities
1. Migration
2. Intercalation
3. Change in cell shape
4. Change in cell adhesiveness
5. Change in the rate of cell division
6. Ingression
7. Apoptosis
A
Mesenchymal Type
10
Q
Mesenchymal Type and Epithelial Type are Regulated by
A
Regulated by gene activity
11
Q
Regulation by gene expressions in Mesenchymal Type and Epithelial Type
A
Expression of genes for cyclins & cd kinases
Expression of regulatory genes for the activation of other genes
Selector genes control the expression of CAMs and SAMs genes
12
Q
SAMs
A
substrate adhesion molecules
12
Q
CAMs
A
cell adhesion molecules
13
Q
genes that code for transcription factors that can regulate activity of other genes
A
Regulatory genes
14
Q
Morphogenetic Movements
An epithelial sheet bends inward to form an inpocketing
Only a few cells are involved
Localized movement of cells
A
Invagination
14
Q
Morphogenetic Movements
Driven by mitosis
A sheet of cells spreads by thinning, that is, the sheet thins, while its overall surface area increases in the other two directions
Can involve a monolayer (i.e. a sheet of cells one cell layer thick) in which case, the indiv. cells must undergo change in shape
A
Epibolly
15
Q
Morphogenetic Movements
Mass movement of cells rolling inward to form an underlying layer via bulk movement of cells
A
Involution
15
Q
Morphogenetic Movements
Decrease in one dimension, increase in the other dimension (ex. Narrower but longer, narrower but thicker)
Coupled with convergent thickening
Two or more rows of cells intercalate, but the intercalation is highly directional
A
Convergent extension
15
Morphogenetic Movements
Convergent extension is Coupled with
convergent thickening
16
Morphogenetic Movements
Cells converge by __________ perpendicular to the axis of extension
intercalating
17
Morphogenetic Movements
Splitting of layers of cells
Delamination
17
Morphogenetic Movements
The process by which tissue elongates along the anterior-posterior (AP) axis, and becomes narrower along the medio-lateral (ML) axis
Convergent extension
17
Morphogenetic Movements
Involves the tissue becoming thicker in the direction at right angles to the convergent extension
Convergent thickening
17
Morphogenetic Movements
Delamination Ex:
formation of epiblast and hypoblast from ICM
18
Morphogenetic Movements
Regulated by gene activity
Passive movement of cells and Migration of cells
19
Morphogenetic Movements
Passive movement of cells and Migration of cells
amoeboid migration
mesenchymal migration
collective migration
19
Morphogenetic Movements
Two or more rows of cells move between one another, creating an array of cells that is longer (in one or more dimension) but thinner
Results to convergent extension
Intercalation
20
Morphogenetic Movements
Cells leave an epithelial sheet by transforming into freely migrating mesenchyme cells into a cavity
Ingression
21
Change in cell shape and position
Formation of outer and inner cells towards 16-cell stage in mammalian embryo
Polarization: inside → ICM, outside → trophoblast
22
Formation of _________ cells help in the formation of the blastopore
bottle-shaped
23
Apoptosis
Apoptosis
24
Change in cell adhesiveness
Cortex tension and cell-cell adhesion determine the shape of multicellular aggregates and the sorting order in heterotypic aggregates
Tissue level
25
Change in cell adhesiveness
Interface-specific localization of cadherins and the actomyosin cortex determine the shape and the strength of the adhesion contact between two cells
Cellular level
26
CAMs examples
Compaction of blastomeres in mammalian blastocyst
At 8-cell stage, there is maximized point of cell-to-cell contact
26
Change in cell adhesiveness
The interaction between tissues, forming at different phases of development and characterized by different cortical and adhesive properties, controls correct germ layers formation during gastrulation
Embryonic level
27
are morphoregulatory molecules
CAMs and SAMs
28
CAMs and SAMs
Facilitate formation of cell-cell contact
Undergo dynamic expression patterns correlated with cell fates
Reversible adhesion; quick attachment/detachment
CAMs (adhesion molecules)
29
CAMs examples
high expression in prospective epidermis
E-cadherin
30
CAMs examples
high-expression in prospective neural plate
N-cadherin
31
SAMs (substrate adhesion molecules)
Examples
Laminin, fibronectin, integrins (present in ECM)
32
Amphibian Gastrulation
Determines the site of the dorsal lip of the blastopore
Gray crescent
32
CAMs and SAMs
Establish structural relationship between cells and the ECM; cell to ECM contact
Provide contact guidance to migrating cells
SAMs (substrate adhesion molecules)
33
gene expression where Embryonic cells synthesize stage-dependent and region-specific ECM components in accord with cell activities
Spatio-temporal gene expression
33
Role of CAMs and SAMs in morphoregulatory cycles rundown
Step-by-step explanation of the cycle
1️⃣ Selector genes
These are master regulatory genes (like homeobox/Hox genes) that determine cell identity and pattern formation.
They control:
Which CAMs and SAMs a cell will express.
How strongly cells adhere or migrate.
🧬 Output → Activates transcription of CAM/SAM genes.
2️⃣ CAMs/SAMs genes
These encode cell adhesion molecules (CAMs) and substrate adhesion molecules (SAMs) — the physical mediators of adhesion.
🧫 Example: E-cadherin, N-cadherin, integrins, fibronectin.
🧬 These genes are transcribed and translated → CAM/SAM proteins are synthesized and deployed to the cell surface or extracellular matrix.
3️⃣ CAM/SAM synthesis and deployment
Cells produce and position these adhesion molecules on their membranes or ECM.
➡️ These molecules now interact with:
Other cells (cell–cell adhesion)
The extracellular matrix (cell–ECM adhesion)
4️⃣ CAM/SAM interactions with other cells or ECM
Once CAMs and SAMs bind:
They form physical junctions (tight, adherens, focal contacts)
They also trigger intracellular signaling cascades (through integrins, cadherins, etc.)
⚙️ These signals influence the cytoskeleton → cell shape, polarity, and motility.
5️⃣ Cell–cell adhesion
Through CAM–CAM or CAM–SAM interactions, tissues acquire structure and integrity.
But adhesion is dynamic — it can weaken or strengthen depending on morphogenetic needs (e.g., epithelial–mesenchymal transition).
6️⃣ Cell movements and shape changes
The intracellular signaling from adhesion interactions causes:
Cytoskeletal remodeling (actin, myosin)
Cell migration, invagination, folding
➡️ These mechanical changes drive morphogenesis — the physical shaping of tissues.
7️⃣ Morphogenesis
As tissues form and cells rearrange, they also generate intercellular signals (via growth factors, morphogens like FGF, BMP, Wnt).
These signals feed back to:
Activate or repress selector genes
Modify CAM/SAM expression
8️⃣ Intercellular and intracellular signaling
The system closes the loop:
New signaling patterns modify gene expression
This changes the levels or types of CAMs/SAMs
The cycle begins again, refining tissue structure
33
Amphibian Gastrulation
Formed by the formation of the bottle-shaped cells
Invagination
Blastopore
34
Amphibian Gastrulation
Cells migrate from dorsal lip of blastopore to the other side guided by the __________ (will form the anterior axis)
SAM fibronectin
34
Amphibian Gastrulation
Cells at the animal hemisphere are going under mitotic division, which causes them to
Causes them to spread
Epiboly
34
Amphibian Gastrulation
Can also ___________ with the ectoderm and endoderm which causes elongation of the whole embryo during late gastrulation
intercalate
34
Amphibian Gastrulation
Cells also move inward with whhat morphogenic movement
Involution
35
Amphibian Gastrulation
Becomes the site of cell turnover
Dorsal lip of blastopore
36
Amphibian Gastrulation
Migration of cells gradually establishes the
body axis
36
Amphibian Gastrulation
Migration of cells gradually establishes theCells at the vicinity of the dorsal lip of the blastopore that cannot enter anymore forms the
chordamesoderm
37
Amphibian Gastrulation
Pick up point for neurulation
Has a power influence on the formation of the neural tube
Chordamesoderm
37
Amphibian Gastrulation
Dorsal lip of the blastopore with the residing chordamesoderm
Chief cell organizer of the embryo
38
Avian Gastrulation
Blastoderm 2 parts
Area pelucida
Area opaca
39
Avian Gastrulation
rundown
Blastodisk leaves after fertilization → Blastoderm
Subgerminal cavity forms underneath the blastoderm
Blastoderm delaminates → Epiblast & primary hypoblast
Blastocoel forms at the expense of the subgerminal cavity
Primitive streak forms at the Epiblast
Cells delaminate and ingress from the epiblast into subgerminal cavity
Ingressing cells form the primary hypoblast
Cells from posterior margin (secondary hypoblast) migrate anteriorly and join the primary hypoblast
Epiblast and hypoblast converged at the margins of the area opaca
Blastocoel is formed between E & H
Epiblast will form embryo proper
Hypoblast will contribute to the formation of extraembryonic membranes
40
Avian Gastrulation
Primitive streak forms at the _______
Epiblast
41
Avian Gastrulation
Designates the future posterior end and anterior enf of the embryo
Primitive streak
41
Avian Gastrulation
Translucent region occupied by the blastoderm and the subgerminal space
Area pellucida
42
Avian Gastrulation
Opaque region because of the close contact with the underlying yolk
Its cells involved in the processing of the yolk
Area opaca
42
Avian Gastrulation
Cell thickening at posterior margin of area pellucida
Induces formation of primitive streak in avian
Koller’s sickle
43
Formation of Primitive Streak (Avian)
rundown
Cells from the lateral region of the posterior epiblast migrate towards the midline
Koller’s sickle induces the formation of the primitive streak
Cells forming the primitive streak migrate anteriorly
Primitive streak lengthens and narrows
Length of the area pellucida defines the anterior-posterior axis of the developing embryo
As more cells converge towards the midline, a depression forms within the streak, the primitive groove
A thickening of cells forms into a knot at the anterior end of the primitive groove, the knot is called the Hensen’s node (primitive knot)
The blastoderm cells migrate over the lips of the primitive streak and into the blastocoel
First migrating cells → ventrally to form the foregut endoderm
Other cells move anteriorly and form the head processes
Other cells move sideways in the blastocoel to form the head mesoderm and lateral mesoderm and the axial mesoderm (chordamesoderm)
Cells at the anterior end are already starting to form organs
The primitive streak regresses
Posterior portions of the embryo (from HN) are still undergoing gastrulation
Hensen’s Node moves posterior
Leaves the head process and the notochord in its wake
The primitive streak with the HN will form the posterior end of the digestive gut, the anus
44
Formation of Primitive Streak (Avian)
A thickening of cells forms into a knot at the anterior end of the primitive groove, the knot is called the
Hensen’s node (primitive knot)
45
Formation of Primitive Streak (Avian)
The HN surrounds a pit, called
continuous with the primitive groove
primitive pit
45
Formation of Primitive Streak (Avian)
The _________ migrate over the lips of the primitive streak and into the blastocoel
blastoderm cells
45
Formation of Primitive Streak (Avian)
Site of cell turnover
Homologous to the dorsal lip of the blastopore
Hensen’s node
46
Formation of Primitive Streak (Avian)
Where cells pass through and undergo ingression
Homologous to the blastopore
Primitive groove
46
Formation of Primitive Streak (Avian)
Coats the ingressing cells
Change adhesive behavior
Adhere to ECM molecules in the blastocoel
Hyaluronic acid
47
Formation of Primitive Streak (Avian)
Pick up point for neurulation
Axial mesoderm (Chordamesoderm)
47
Formation of Primitive Streak (Avian)
Guides migratory behavior of cells from the epiblast
Fibronectin
48
Mammalian Gastrulation
Amniotic ectoderm and the rest of the hypoblast and trophoblast will contribute to the
placenta
48
Formation of Primitive Streak (Avian)
Avian gastrulation is an ingression of epiblastic cells which form
mesenchyme cells
48
Mammalian Gastrulation
Marked with the formation of a _____________ similar with that of avian embryo
primitive streak
49
Mammalian Gastrulation
rundown
🧫 1. Overview
Gastrulation is the process by which a simple bilaminar disc (two layers) is reorganized into a trilaminar disc (three layers):
👉 Ectoderm, Mesoderm, and Endoderm
This marks the beginning of body plan establishment — setting up the anterior–posterior, dorsal–ventral, and left–right axes.
🥚 2. Before Gastrulation — The Bilaminar Embryonic Disc
After implantation and early development:
The inner cell mass (ICM) of the blastocyst forms two layers:
Epiblast → dorsal layer
Hypoblast (primitive endoderm) → ventral layer
Together they form the bilaminar embryonic disc, surrounded by:
Amniotic cavity (above the epiblast)
Yolk sac (below the hypoblast)
🧭 3. Formation of the Primitive Streak
Gastrulation begins with the formation of the primitive streak on the caudal (posterior) region of the epiblast.
Cause: Local cell proliferation and migration.
Significance: Establishes body axes:
Anterior–Posterior axis → defined by streak direction
Cranial end → where the primitive node (Hensen’s node) forms
Midline → primitive groove (a furrow)
🧬 Molecular control:
FGF, Wnt, and Nodal signaling regulate streak formation.
🧬 4. Cell Migration Through the Primitive Streak
Epiblast cells migrate inward (invagination) through the primitive streak and replace or insert between existing layers.
This movement produces the three germ layers:
First wave → displaces hypoblast → forms Definitive Endoderm
Second wave → spreads between epiblast and endoderm → forms Intraembryonic Mesoderm
Remaining epiblast → becomes Ectoderm
🧩 5. Formation of the Trilaminar Embryonic Disc
After these migrations, the embryo now has three germ layers:
Layer Origin (from epiblast) Future structures
Ectoderm Cells that stayed on surface Epidermis, nervous system, sensory organs
Mesoderm Cells that migrated between layers Muscle, bone, heart, kidneys, blood, gonads
Endoderm Cells that replaced hypoblast Gut lining, liver, pancreas, lungs
➡️ This is the Trilaminar Embryonic Disc, the foundation for all body tissues.
🌱 6. Additional Structures During Gastrulation
a. Notochordal Process
Formed from cells migrating cranially from Hensen’s node.
Later forms the notochord, a key signaling center for neural induction and body axis patterning.
b. Prechordal Plate
Located anterior to the notochord; important for forebrain and head structure.
🧭 7. Establishment of Body Axes
During gastrulation:
Anterior–Posterior axis → by primitive streak formation
Dorsal–Ventral axis → by position of epiblast vs hypoblast
Left–Right axis → established by signals like Nodal, Lefty, and serotonin from the node
49
Mammalian Gastrulation
Includes the formation of the three primary germ layers
Trilaminar disc formation
50
Mammalian Gastrulation
Pick up point for neurulation
Notochordal process
DEVBIOL
flashcards
Decks in class (16)
# Cards
-
Topic 1: Introduction118
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Topic 1: Introduction part 240
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Topic 2: Gametogenesis28
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Topic 3: Fertilization58
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Topic 4: Cleavage to Blastulation54
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Topic 5: Gastrulation82
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Topic 6: Neurulation55
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Topic 7: Body Axis Formation32
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Topic 8a: Establishment of Germ Layers81
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Topic 8b: Neural Crest Cell72
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Topic 09: Implantation, Fetal Membrane, and Placentation158
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Topic 10: Hormonal Control72
-
Limb Morphogenesis41
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UROGENTIAL SYSTEM17
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Topic 11 : Embryonic Induction and Cell-to-Cell Signalling153
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Topic 12: Embryonic Differentiation108
