Nervous System

Question 1

Describe development of notochord.

Answer 1

The primitive node provides cells that form notochord. The cellular precursors migrate forward and left behind has rodlike aggregation as primitive streak regresses. Notochord also cells fuse with endodermis cells and form a temporary neurenteric canal. Notochordal cells separate from endoderm and form solid notochord.

Question 2

What is the relationship of Nodal to the establishment of the anteroposterior axis and what is the role of Lefty 1 and Cer1?

Answer 2

Lefty 1 and Cer1 block nodal to set up a gradient. Lefty and Cer1 are towards the cranial end and will have low levels of nodal while the posterior end has high levels.

Question 3

How is Wnt3 related to Nodal?

Answer 3

Wnt3 is at the posterior end of the epiblast and signals Nodal to be activated.

Question 4

What signaling molecules are involved in inhibition of posterior structure?

Answer 4

Cerberus-Like inhibits posterior structures and is from the anterior visceral endoderm.

DKK-1 also inhibits development of posterior structures and originates from anterior visceral endoderm and blocks Wnt.

Question 5

What signaling molecule from primitive node are involved in neural induction?

Answer 5

Noggin and Chordin both induce neural and are from primitive node.

Question 6

Nodal is a signaling molecule produced by primitive node what is it s role in the induction of primitive streak and left right symmetry?

Answer 6

Nodal induces the primitive streak…..

Question 7

What is the source land role of signaling molecules Cerberus-like and DKK-1 in the development of anteriorposterior axis?

Answer 7

They come from Anterior visceral endoderm and they inhibit development of posterior structures.

Question 8

What are the origin and effects of TF’s Goosecoid and Brachyury in regard to early primitive streak?

Answer 8

Goosecoid originates from primitive node and it activates Chordin and nogggin.

Brachcyury originates from the primitive streak and it effects notochord formation and allows for normal movements of cells through primitive streak.

Question 9

What genes are targeted by Goosecoid?

Answer 9

Chordin and Noggin

Question 10

What are the effects of Foxa-2 on early primitive streaks?

Answer 10

Establishment of primitive node and initiates notochord function. Also established midline structures cranial to node.

Question 11

What are classical markers of organizer region in vertebrates?

Answer 11

Chord in, Goosecoid, and Fox-2

Question 12

In late primitive streak what signaling molecule induces axial structures?

Answer 12

Sonic Hedgehog

Question 13

In late primitive streak what signaling molecule is necessary for head formation?

Answer 13

Cerberus-1

Question 14

In late primitive streak stage what signaling molecules are needed for neural induction and what is their origin?

Answer 14

Noggin Chordin and Shh they are all from the notochord.

Question 15

In late primitive streak stage what signaling molecules are released from primitive streak activate Hox genes?

Answer 15

RA, Wnt, FGF

Question 16

Describe experiments on amphibian and higher. Vertebrates that led to understanding of neural induction.

Answer 16

The dorsal lip of the blastopore is the organizer. The took dorsal lip from a donor blastocyst and transferred it into the blastocoele and it now has two blastopores. The result is two separate embryos.

Took section of hensen’s node prone primitive streak and placed it into a donor. The embryo resulted in host embryo and an induced neural tube.

Question 17

Difference between determination and differentiation

Answer 17

Determination is when cells or part of embryo becomes restricted to a certain dev path, it becomes committed to a cell line.

Differentiation is a set of changes involved in the specialization of structure and function, results in luxury molecules.

Question 18

What is the first sign of asymmetry in early development? Role of Nodal and Lefty?

Answer 18

Fist sign involves the beating of cilia around the primitive node. Asymmetrical beating results in a directional current and expression of TGF-Beta.

Nodal is symmetry breaking molecule in the left side of the embryo.
Lefty-1 is on the left side of the primitive streak.

Question 19

Describe the distribution of CAM’s in early ectoderm.

Answer 19

E Cadherins are found in the preinduced ectoderm along with N-CAM.
The ectoderm then evolves to just become E cadherins.

The neural tube will have N-CAM’s and N- cadherins.

Question 20

List stages of neural tube development.

Answer 20

1. Formation of thickened neural plate
2. Shaping of neural plate
3. Folding of neural plate
4. Formation of neural tube

Question 21

Explain process of convergent extension.

Answer 21

Involves migration of ectodermal cells to the midline. Ectodermal cells elongate along the anterior-posterior axis and become thinner forming elongated narrow plate.

Question 22

What role does planar polarity play in formation of neural plate?

Answer 22

It causes cells to become oriented along an axis in a flat plane. It is caused by asymmetric distribution of planar cell polarity proteins Dishevelled and Prickle.

The PCP convert elliptical gastrula into keyhole shaped neurula and are important in folding of plate into the tube.

Question 23

Describe significance of median and lateral hinge points in neural tube formation.

Answer 23

Median hinge point is induced by notochord and involves changing columnar cells shape to pyramidal shaped cells and apical constriction.

Lateral hinge points involve apical constriction by actin filaments.

Question 24

What roles do Oxt-2, Gbx-2 Wnt-8, Shh, FGF-8 play in the segmentation of spinal cord?

Answer 24

Otx-2: expressed in forebrain/midbrain,, Isthmmic organizer is established by boundary between Otx-2 and God-2 and Releases Wnt-1 and FGF-8.
Gbx-2: Expressed in hindbrain region
Wnt-8: establishes anterior posterior gradient
Shh: Secreted by anterior neural ridge signaling center important for organizing telencephalon, diencephalon olfactory area and pituitary gland.
FGF-8: released posteriorly from the isthmic organizer also secreted from anterior neural ridge signaling center (same function as Shh)
RA:

Question 25

What roles do Krox 20, Kreisler, Hoxa-1, and RA play in segmentation of hind brain?

Answer 25

Krox-20: related to Rhombomeres 3 and 5
Kreisler and Hoxa-1: Rhombomere 5
RA gradient: R4-7

Question 26

Why is neural crest tissue considered to be a fourth germ layer?

Answer 26

A

Question 27

What is the origin of sensory placodes and with which cranial nerve are they associated?

Answer 27

Trigeminal nerve CN5

Question 28

What is meant by Caudalmost part of the neural plate possesses the properties of a stem cell zone? (Page 96).

Answer 28

A

Question 29

Describe Nodal’s role and Lefty-1 role in left right asymmetry.

Answer 29

Nodal sets up the later asymmetry of internal organs and forms Pitx-2. Nodal is swept to left of primitive node by ciliary current.

Lefty-1 blocks diffusion of molecules to the right side and is found on left side of embryo.

Question 30

Formation of neural tube?

Answer 30

Due to fusion of apical surfaces of neural folds and it is mediated by glycoconjugates. Closure of the tube begins midway and extends cranially and caudally at day 21.

Question 31

Anterior neural tube segmentation Tripartite brain?

Answer 31

Prosencephalon
Mesencephalon
Rhombencephalon

Question 32

Anterior Neural tube segmentation Pentapartite brain?

Answer 32

Prosencephalon: Telencephalon and Diencephalon
Mesencephalon
Rhombencephalon: Metencephalon and Myelencephalon