Lecture 10: Nervous System Induction

Question 1

Steps in the formation of the notochord:

Answer 1

• Primitive node provides the source of cells that will form the notochord.
• Cellular precursors of the notochord migrate anteriorly and are then left behind as a rodlike aggregation as the primitive streak regresses.
• Notochordal cells fuse with flanking endodermal cells and temporarily form a neurenteric canal.
• Notochordal cells separate from the endoderm and aggregate to form a solid definitive notochord.

Question 2

Inductive functions of the notochord:

Answer 2

• Important in the formation of many axial structures:
• i.e., Shh (signal)
• Induces overlying ectoderm to convert to neural ectoderm:
• i.e., Foxa-2 and Goosecoid (transcription factors)
• i.e., Noggin and Chordin (signals)
• Specifies identity of certain cells within the early nervous system.
• Transforms certain mesodermal cells of the somites into vertebral bodies.
• Stimulates earliest steps in the development of the pancreas.

Question 3

Prechordal Plate

Answer 3

• Also referred to as the head organizer.
• Formed by early cells that pass through the primitive node.
• Source of signals such as shh involved in the ventral patterning of the forebrain.
• Source of signals important for the survival of neural crest cells that emigrate from the early forebrain.

Question 4

Wnt3

Answer 4

Wnt3
Posterior epiblast
TARGET: Epiblast cells
Induces expression of nodal

Question 5

Lefty 1 and Cer 1

Answer 5

Anterior hypoblast
Target: NODAL
Blocks expression of Nodal in anterior epiblast confines its expression to posterior epiblast

Question 6

NODAL

Answer 6

Epiblast cells
Target: Multiple
Establishes a posterior signaling center which induces formation of the primitive streak

Question 7

anteroposterior axis.

Answer 7

Note that expression of nodal in the posterior epiblast and blocking of nodal in the anterior epiblast results in the establishment of the anteroposterior axis.

Question 8

Cerebrus-like

Answer 8

Origin: Ant. visceral endoderm

Effects: Inhibits development of posterior structures

Question 9

DKK1

Answer 9

Origin: Ant. visceral endoderm
Target: Blocks Wnt
Effects: Inhibits development of posterior structures

Question 10

Otx-2 Ant.

Lim-1

Answer 10

Target:Ant. visceral endoderm
Effects: Associated with induction of anterior CNS/head (See Figure 5.9)

Question 11

Noggin

Answer 11

Origin: Primitive Node

Effect: Neural Inducer

Question 12

Chordin

Answer 12

Origin: Primitive Node

Effect: Neural Inducer

Question 13

Nodal

Answer 13

Origin: Primitive Streak

Effect: Induces primitive streak and helps to establish left-right symmetry

Question 14

Goosecoid

Answer 14

Origin: Primitive Node

Target: chordin, noggin

Effect Establishment of primitive node; initiates notochord function; establishes midline structures cranial to node

Question 15

Foxa-2

Answer 15

Origin: Primitive node
Target: Multiple
Effect: Establishment of primitive node; initiates notochord function; establishes midline structures cranial to node

Question 16

Wnt-3

Answer 16

Origin: Primitive streak

Induces expression of nodal

Question 17

Brachyury

Answer 17

Prim Streak

Notochord formation; normal movements of cells through primitive streak

Question 18

Shh (late primitive streak stage)

Answer 18

Prechordal plate
multiple targets
Induces axial structures

Question 19

Noggin
Chordin
Shh

Answer 19

Notochord

Effect: Neural Inducer

Question 20

Goosecoid

Foxa-2

Answer 20

Origin: Prechordal Plate
Target: Chordin, noggin
Effect: activates genes

Question 21

Explain why the amphibian dorsal lip is referred to as the organizer and explain its role in neural induction.

Answer 21

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Question 22

Describe the role of the notochord as a primary organizer.

Answer 22

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Question 23

Determination:

Answer 23

A process by which a cell or part of an embryo becomes restricted to a given developmental pathway. The point at which a cell becomes committed to a specific cell line.

Question 24

Differentiation:

Answer 24

A complex of changes involved in the progressive specialization of structure and function; often resulting in the formation of luxury molecules.

Question 25

Factors that determine asymmetry:

Answer 25

• First sign of asymmetry involves the beating of cilia around the primitive node:
• Asymmetrical beating results in a directional current and expression of TGF-β molecules :
• Nodal:
• Symmetry breaking molecule in the left side of the
embryo
• Lefty-1:
• Left side of the primitive streak

Question 26

Asymmetrical current occurs between

Answer 26

2 and 6-somite stage in mouse.

Question 27

Symmetry:
Nodal:

Answer 27

• Swept to left side of primitive node by ciliary current • Stimulates multiple gene expression pathways via:
• Pitx-2

Question 28

Symmetry:

Lefty-1

Answer 28

• Expressed on left side of the embryo

* Blocks diffusion of molecules to the right side

Question 29

Additional factors for symmetry:

Answer 29

• Shh
• Retinoic acid
• FGF-8

Question 30

A review of cell adhesion molecules is given on pages 85-89. Review on own and review Figure 5.16.

Answer 30

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Question 31

Be able to describe the distribution of CAMs in the early ectoderm (see Figure 5.17 and related text).

Answer 31

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