Xenopus and Zebrafish development

Question 1

What is gastrulation?

Answer 1

A crucial early stage of embryonic development where a one-layered blastula is reorganized into a two- or three-layered embryo, called a gastrula.

Question 2

Define body plan.

Answer 2

The basic organization and arrangement of an animal’s body, including features like symmetry, segmentation, and the arrangement of organs and tissues.

Question 3

What are germ layers?

Answer 3

The fundamental cell layers that form during early embryonic development in most animals, leading to the formation of various tissues and organs.

Question 4

List the three germ layers typically found in triploblastic animals.

Answer 4

• Ectoderm
• Mesoderm
• Endoderm

Question 5

What is differentiation?

Answer 5

The process by which cells become specialized, acquiring distinct structures and functions.

Question 6

What is morphogenesis?

Answer 6

The biological process by which a cell, tissue, or organism develops its shape and structure.

Question 7

What does the term ‘fate’ refer to in developmental biology?

Answer 7

The specific cell types that a cell is capable of generating as it differentiates.

Question 8

What is the significance of Conrad Waddington’s ‘Epigenetic landscape’?

Answer 8

It depicts how a cell is guided to one fate or another as it becomes progressively restricted in the array of different cell types it can generate.

Question 9

What are the three core pieces of evidence that prove a mechanism in development?

Answer 9

• Is it there at the right time and place?
• Is it required?
• Is it sufficient?

Question 10

What is the role of signalling in development?

Answer 10

It is the mechanism by which cells communicate to control decision-making processes like proliferation, apoptosis, and dynamic cell behaviors.

Question 11

What is embryonic induction?

Answer 11

The process by which tissues and cell populations release signals to change and organize the fate of neighboring tissues.

Question 12

What type of cleavage do Xenopus embryos undergo?

Answer 12

Holoblastic cleavage, meaning that cytokinesis goes through the whole of the fertilized egg.

Question 13

What is the significance of the grey crescent in Xenopus development?

Answer 13

It is required to get a complete embryo to form.

Question 14

What happens at the sperm entry point during fertilization?

Answer 14

It triggers a reorganization of the microtubule cytoskeleton, aligned to the point of entry.

Question 15

True or False: Proper microtubule alignment is essential for establishing the complete body axis.

Answer 15

True.

Question 16

What is Wnt’s role in embryonic development?

Answer 16

Wnt acts as a dorsalizing agent and is involved in establishing the body axis.

Question 17

Who is credited with the discovery of the Spemann-Mangold organizer?

Answer 17

Hilde Mangold, under the supervision of Hans Spemann.

Question 18

What does Activin do in the context of germ layer specification?

Answer 18

It can induce marginal zone markers in ectodermal explants in a concentration-dependent manner.

Question 19

What is the default state of early ectoderm in Xenopus?

Answer 19

Anterior neural tissue.

Question 20

What role do Noggin and Chordin play in neural induction?

Answer 20

They inhibit BMP signals to activate the default neural program.

Question 21

What is the Yolk Syncytial Layer in zebrafish embryos?

Answer 21

A line of cells that have their cytoplasms open to the yolk and act as an important signaling center.

Question 22

List the three key morphogenetic processes involved in zebrafish gastrulation.

Answer 22

• Epiboly
• Involution
• Dorsal convergence

Question 23

Define totipotent cells.

Answer 23

Cells that can generate all embryonic and extraembryonic cells.

Question 24

Define pluripotent cells.

Answer 24

Cells that can generate all embryonic cells.

Question 25

What is the significance of BMP4 in early ectoderm specification?

Answer 25

Adding BMP4 is sufficient to revert cells from an anterior neural state back to being epidermal.

Question 26

What does the dissociation of ectodermal cells in Xenopus lead to?

Answer 26

Cells revert to an anterior neural state ## Footnote The default state of the ectoderm is anterior neural tissue, which is maintained by a signal that is lost upon dissociation.

Question 27

What is sufficient to revert ectodermal cells back to being epidermal?

Answer 27

BMP4 ## Footnote BMP4 acts as a signal that encourages the cells to adopt an epidermal fate.

Question 28

What signals do the organiser release to inhibit BMP and activate the neural programme?

Answer 28

* Noggin * Chordin ## Footnote These signals are crucial for activating the default neural program by inhibiting BMP.

Question 29

What happens to the mesoderm underlying the neural plate during gastrulation?

Answer 29

It can be removed and transplanted to a host embryo ## Footnote This transplantation shows that the underlying mesoderm is important for establishing the anterior-posterior axis of the neural plate.

Question 30

What is the significance of transplanting pieces of mesoderm from under the neural plate?

Answer 30

Induces fated brain tissue upon transplantation ## Footnote This indicates that the underlying mesoderm has a role in patterning the neural plate.

Question 31

What does the 'activation-transformation' model describe?

Answer 31

The specification of ectoderm as neural followed by transformation into posterior spinal cord ## Footnote This model is based on experiments by Spemann and Hilde Mangold.

Question 32

What effect does the position of early ectoderm grafts have?

Answer 32

Alters the proportions of anterior-posterior nervous tissue ## Footnote This indicates that positional information influences the fate of ectodermal tissue.

Question 33

Why are zebrafish advantageous for imaging during development?

Answer 33

Their cells are almost entirely transparent ## Footnote This transparency allows for direct observation of cell behaviors in their normal context.

Question 34

What key behaviors are involved in zebrafish gastrulation?

Answer 34

* Radial intercalation * Medio-medic-lateral intercalation ## Footnote These behaviors help spread embryonic cells over the yolk and elongate the body axis.

Question 35

What is a key feature of zebrafish and Xenopus development?

Answer 35

External development ## Footnote Their embryos develop outside of the mother or a hard egg shell, facilitating experimental manipulation.