Lecture 5 -7 (Set A)

86 Questions

What is the characteristic of blastulation in mammals?

Generation of ICM and tropoblast

During gastrulation, what is the main goal of establishing the dorsal lip of the blastopore?

To lay down the primitive gut

What is the significance of the blastocoel in mammalian blastulation?

It is the space between the epiblast and hypoblast

What is the characteristic of the ectoderm and endoderm?

Epithelial type with a flat sheet of cells

What is the significance of cell movements during gastrulation?

To acquire positional information

What is the characteristic of the mesoderm?

Mesenchymal type with plenty of ECM

What is the significance of the archenteron?

It is the precursor of the digestive gut

During gastrulation, what is the significance of the formation of the blastopore?

It initiates the formation of the primitive gut

What is the characteristic of the behavior of ectoderm and endoderm?

They can spread, roll, fold, buckle, and bend

What is the characteristic of the behavior of mesoderm?

They migrate individually

What is the resulting embryonic phase at the end of the blastulation process in amphibians?

A hollow ball of cells with a cavity

Where is the future dorsal side of the embryo located at the end of blastulation in amphibians?

At the marginal zone (MZ)

What is the term for the cavity found in the avian embryo at the end of blastulation?

Blastocoel

What is the resulting structure formed at the end of blastulation in avians?

A stack of cell layers

What is the term for the layer of cells that forms underneath the blastoderm in avian blastulation?

Hypoblast

What is the process by which the blastoderm cells absorb the fluid in the yolk underneath to form the subgerminal cavity?

Absorption

What is the relationship between the end of blastulation and the start of gastrulation in avians?

There is a swift transition from the last part of blastulation to early gastrulation

What is the term for the cavity formed underneath the blastoderm in avian blastulation?

Subgerminal cavity

What is the primary function of cyclins and cyclin dependent kinases in the cell cycle?

Regulating cell division by controlling the rate of mitosis

Which type of cell can undergo epithelial-mesenchymal transition during embryonic development?

Ectoderm, endoderm, and mesoderm

What is the term for the process by which cells spread out and thin, resulting in an increase in surface area?

Epiboly

Which type of morphogenetic movement involves the migration of cells?

Involution

What is the role of transcription factors in regulating gene expression?

Activate or deactivate gene expression

What is the term for the process by which cells undergo a change in shape?

Change in cell shape

Which type of gene is responsible for regulating the expression of other genes?

Regulatory gene

What is the term for the process by which cells move from a layer of flat cells to a cavity?

Ingression

What is the role of CAMs and SAMs in embryonic development?

Morphoregulation

Which type of morphogenetic movement involves the inpocketing of cells to form a cavity?

Invagination

What is the process by which a double-layered epithelium becomes monolayered?

Involution

What is the term for the movement of cells that results in a change in the dimensions of a sheet of cells?

Convergent extension

What is the result of intercalation of cells in a highly directional manner?

Convergent extension

What is the type of cell migration that occurs in primordial germ cells?

Ameboid migration

What is the process by which tissue becomes thicker in the direction at right angles to the convergent extension?

Convergent thickening

What is the term for the formation of the epiblast and hypoblast?

Delamination

What is the result of the process of involution in the development of an amphibian oocyte?

Formation of the blastopore

What is the term for the mass movement of cells rolling inward to form an underlying layer?

Involution

What is the reason for the slower rate of cell division in the vegetal pole?

Impeded cell division due to the thick yolk

What is the term for the movement of cells that results in a change in the shape of individual cells?

Change in shape of individual cells

What is the correct sequence of migration of primordial germ cells in the embryo?

From the yolk sac endoderm to the dorsal mesentery, then to the genital ridges

Which type of migration involves the movement of neural crest cells and the head mesenchyme?

Mesenchymal migration

What is the primary role of genes in morphogenetic movements?

To regulate the expression of CAMs and SAMs

What is the result of intercalation during embryonic development?

Convergent extension and convergent thickening

What is the term for the process by which cells leave an epithelial sheet to form a cavity?

Inggression

What is the term for the programmed cell death that occurs during embryonic development?

Apoptosis

What is the result of change in cell shape and position during the 16-cell stage of the mammalian embryo?

Polarization of cells

What is the role of cadherin and the actomyosin cortex in cellular adhesion?

To determine the shape and strength of the adhesion contact between two cells

What is the term for the process by which cells acquire different degrees of adhesiveness from the cellular level to the tissue level?

Change in cell adhesiveness

What is the term for the process by which cells undergo a change in shape and position, resulting in the formation of a cavity?

Change in cell shape and position

At what stage of development do transcription factors control the expression of CAMs and SAMs?

During embryonic stage

What is the result of cell-to-cell adhesion interactions between CAMs and SAMs and other cells?

Changes in cell shape and movements

What is the role of feedback on selector genes during morphogenesis?

To activate more CAMs/SAMs genes

What is the significance of the gray crescent region in amphibian gastrulation?

It determines the site of the dorsal lip of the blastopore

What is the outcome of invagination during amphibian gastrulation?

Formation of the dorsal lip of the blastopore

What is the role of fibronectin in amphibian gastrulation?

It provides contact guidance to migrating cells

What is the significance of the chordamesoderm in amphibian gastrulation?

It has a powerful influence on neurulation

What is the difference between the area pellucida and the area opaca in avian gastrulation?

The area pellucida is lighter, while the area opaca is darker

What is the significance of the blastoderm in avian gastrulation?

It undergoes cleavage division

What is the role of CAMs and SAMs in embryonic cell positioning?

They are involved in cell adhesion and intercellular signaling

What is the primary factor that determines the shape of multicellular aggregates and the sorting order in heterotypic aggregates?

Cortex tension and cell-cell adhesion

Which of the following CAMs is highly expressed in prospective epidermis?

E-cadherin

What is the primary function of SAMs?

Establish structural integrity of cells with the surrounding matrix

What is the characteristic of CAMs and SAMs in terms of adhesion?

Reversible adhesion, quick attachment/detachment

What is the term for the process of regulating morphogenesis during development, adaptation, and regeneration?

Morphoregulation

What is the primary role of selector genes?

Code for transcription factors

What is the significance of spatio-temporal gene expression in embryonic development?

Ensures that gene products are present at the right time and place

What is the region where cells undergo ingression during avian gastrulation?

Primitive groove

Which of the following molecules is NOT a type of morphoregulatory molecule?

Laminin

Which structure is formed by the migratory cells that move ventrally during avian gastrulation?

Foregut endoderm

What is the term for the molecules that facilitate cell-cell contact and cell-ECM contact?

Adhesion molecules

What is the role of fibronectin in avian gastrulation?

Guiding migratory behavior of cells from the epiblast

What is the significance of the coordinated expression and function of CAMs, SAMs, and JAMs?

Provides an essential link between genetic and epigenetic mechanisms

What is the destination of the cells that move sideways during avian gastrulation?

Lateral mesoderm and axial mesoderm

What is the result of the migration of cells into the blastocoel during avian gastrulation?

Displacement of the hypoblastic cells

What is the direction of movement of the primitive streak during avian gastrulation?

Posteriorly

What is the role of hyaluronic acid in avian gastrulation?

Coating ingressing cells and changing their adhesive behavior

What is the term for the process by which epiblastic cells form mesenchyme cells during avian gastrulation?

Ingression

What is the significance of the area pellucida?

It is a translucent region occupied by the blastoderm and the subgerminal space.

What is the process by which cells fall off from the epiblast into the subgerminal cavity?

Delamination

What is the term for the thickening of cells at the posterior margin of the area pellucida?

Koller's sickle

What is the result of the convergence of the epiblast and hypoblast at the margins of the area opaca?

The thickening of the area opaca

What is the significance of the blastocoel in avian gastrulation?

It is a cavity that forms between the epiblast and hypoblast.

What is the process by which cells from the posterior margin migrate towards the midline?

Convergence

What is the term for the knot formed at the anterior end of the primitive groove?

Hensen's node

What is the significance of the formation of the primitive streak?

It designates the future posterior end of the embryo.

What is the relationship between the epiblast and hypoblast?

The epiblast forms the embryo proper, while the hypoblast forms the extraembryonic membranes.

What is the term for the depression that forms within the primitive streak?

Primitive pit

Study Notes

Blastulation

In amphibian development, the resulting embryonic phase is a hollow ball of cells with a cavity called the blastocoel
The future dorsal side of the embryo is established at the end of blastulation
The site where the first falling off cells to form the hypoblast represents the future posterior end of the embryo

Avian Blastulation

The resulting stack of cell layers at the end of blastulation consists of the epiblast and hypoblast
The blastoderm forms when the blastodisc starts cleaving
The formation of the epiblast and hypoblast marks the start of the early phase of gastrulation
The blastoderm cells underneath the hypoblast fall off and coalesce to form the hypoblast
The blastocoel is the cavity between the epiblast and hypoblast

Mammalian Blastulation

The end of blastulation results in 2 distinct populations of cells: the ICM (inner cell mass) and the tropoblast or trophectoderm, with the blastocoel
Polarity is not yet established in mammalian development
The embryo proper has yet to form in the ICM

Gastrulation

The most distinguishing feature of gastrulation is the formation of the dorsal lip of the blastopore
Gastrulation establishes the precursor of the digestive gut, called the primitive gut or archenteron
The main goals of gastrulation are:
- Laying down the primitive gut
- Cell movements and rearrangements (morphogenetic movements)
- Starting to acquire positional formation
- Forming the three germ layers (ectoderm, endoderm, and mesoderm)

The Three Germ Layers

Ectoderm and endoderm are epithelial type (flat sheet; closely-packed cells; little ECM)
Mesoderm is mesenchymal type (loosely-arranged; plenty of ECM)
Each germ layer has distinct characteristics and behaviors

Morphogenetic Movements

Examples of morphogenetic movements include:
- Invagination (inpocketing of cells)
- Epiboly (spreading of cells)
- Involution (mass movement of cells rolling inward)
- Convergent extension (intercalation of cells in a specific direction)
- Delamination (splitting of a layer of cells)
- Passive movement of cells and migration of cells

Regulation of Morphogenetic Movements

Morphogenetic movements are regulated by gene activity
Genes are activated to form gene products that facilitate morphogenetic movements
CAMs (cell adhesion molecules) and SAMs (substrate adhesion molecules) are morphoregulatory molecules that regulate morphogenesis during development
Spatio-temporal gene expression ensures that gene products are present at the right time and place during development### Cell-to-Cell Adhesion Interactions
Cell-to-cell adhesion interactions cause various cell movements, including changes in cell shape, movements, ingression, and involution.
These movements drive morphogenesis, and cells move, change shape, and interact with other cells or new neighboring cells.
This leads to new cell-to-cell interactions and new intercellular signaling, which can have feedback on selector genes.

Amphibian Gastrulation

The gray crescent region determines the site of the dorsal lip of the blastopore (DLB).
The dorsal lip of the blastopore forms through invagination, and the bottle-shaped cells cause invagination.
Epiboly occurs when cells in the animal hemisphere undergo mitotic division, spreading, and thinning.
Involution occurs when cells move inward due to a depression, and they can intercalate with the ectoderm and endoderm.
The three morphogenetic movements - invagination, epiboly, and involution - occur simultaneously in amphibian gastrulation.
The dorsal lip of the blastopore is the site of cell turnover, and the involute cells migrate from the dorsal lip to the other side, guided by fibronectin.

Avian Gastrulation

The blastoderm is the black structure on top of the yellow yolk, and it undergoes cleavage division.
The blastoderm is divided into the area pellucida (translucent region) and the area opaca (opaque region).
The primitive streak forms at the epiblast and designates the future posterior end of the embryo.
The blastoderm eventually delaminates, forming the epiblast and the primary hypoblast, and the blastocoel forms at the expense of the subgerminal cavity.
The formation of the primitive streak involves the delamination of cells from the epiblast, which ingress into the subgerminal cavity, forming the primary hypoblast.
The cells from the posterior margin migrate anteriorly and join the primary hypoblast, forming the secondary hypoblast.
The primary hypoblast with secondary hypoblast interdigitating results in the elongation of the hypoblast.
The epiblast and hypoblast converge at the margins of the area opaca, forming a thickening, which is the Koller's sickle.
The Koller's sickle induces the formation of the primitive streak in avian gastrulation.

Formation of the Primitive Streak

Cells from the lateral region of the posterior epiblast migrate towards the midline, inducing the formation of the primitive streak.
The primitive streak lengthens and narrows as more cells converge.
A depression forms within the streak, the primitive groove, surrounded by primitive folds.
A thickening of cells forms into a knot at the anterior end of the primitive groove, the Hensen's node (primitive knot).
The Hensen's node is homologous to the dorsal lip of the blastopore.
The primitive groove is homologous to the blastopore.

Gastrulation and Morphogenesis

Cells from the epiblast move into the blastocoel, migrating over the lips of the primitive streak and into the blastocoel.
Cells move towards the midline, ingressing through the primitive groove.
The blastocoel cells migrate to form the endoderm, mesoderm, and ectoderm.
Fibronectin guides the migratory behavior of cells from the epiblast, and hyaluronic acid coats the ingressing cells, changing their adhesive behavior.
The first migrating cells move ventrally to form the foregut endoderm, displacing the hypoblastic cells.
The other cells move anteriorly and form the head process, overlying the Hensen's node.
The cells move sideways in the blastocoel to form the head mesoderm and lateral mesoderm.
The axial mesoderm forms the chordamesoderm.
Avian gastrulation is an ingression of epiblastic cells that form mesenchyme cells.
The primitive streak regresses, and the neural structures are pushed anteriorly.
The posterior portions of the embryo are still undergoing late gastrulation.
The Hensen's Node moves posteriorly, leaving the head process and the notochord in its wake.

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