Nervous System Induction

Question 1

What are the inductive functions of the notochord?

Answer 1

• important in the formation of many axial structures (Shh)
• induces overlying ectoderm to convert to neural ectoderm
• 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 2

What transcription factors and signals does the notochord utilize to induce ectoderm to convert to neural ectoderm?

Answer 2

• transcription factors: Foxa-2 and Goosecoid

- signals: noggin and chordin

Question 3

What is the prechordal plate?

Answer 3

• aka 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

What are the steps in the formation of the notochord?

Answer 4

• 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 neuroenteric canal
• notochordal cells separate from the endoderm and aggregate to form a solid definitive notochord

Question 5

What does Wnt3 do?

Answer 5

-acts on epiblast cells and induces the expression of nodal

Question 6

What do Lefty1 and Cer1 do?

Answer 6

-blocks nodal in anterior epiblast and confines its expression to the posterior epiblast

Question 7

What does Nodal do?

Answer 7

• establishes a posterior signaling center which induces formation of the primitive streak (pre-streak)
• establish left-right symmetry (early primitive streak stage)

Question 8

What doe Cerebrus-like do?

Answer 8

• early primitive streak stage

- inhibits development of posterior structures

Question 9

What does DKK-1 do?

Answer 9

• blocks Wnt, early primitive streak stage

- inhibits development of posterior structures

Question 10

What do Otx-2 and Lim-1 do?

Answer 10

• early primitive streak stage

- associated with induction of anterior CNS/head

Question 11

What do Noggin and Chordin do?

Answer 11

• primitive node

- neural inducer

Question 12

What does Goosecoid act on and what does it do?

Answer 12

• acts on chordin and noggin

- activates genes

Question 13

What does Foxa-2 do?

Answer 13

• establishment of primitive node
• initiates notochord function
• establishes midline structures cranial to nodal
• in late primitive streak stage acts on chordin and noggin to activate genes

Question 14

What does Brachyury do?

Answer 14

• notochord formation

- normal movement of cells through primitive streak

Question 15

What does SHH do?

Answer 15

• induces axial structures (prechordial plate)

- neural inducer (notochord)

Question 16

What does Cerebrus-related 1 do?

Answer 16

-normal head formation

Question 17

What does retinoic acid, Wnt, and FGF do in the later primitive streak stage?

Answer 17

• targets Cdx

- induces Hox

Question 18

What does the amphibian dorsal lip do?

Answer 18

-dorsal lip is organizer bc it organizes the formation of the embryo

Question 19

What is the difference between determination and differentiation?

Answer 19

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

Differentiation: a complex of changes involved in the progressive specialization of structure and function, often resulting in the formation of luxury molecules.

Question 20

What are some examples of body asymmetry?

Answer 20

• heart
• looping of gut
• liver
• spleen
• lung lobation

Question 21

What are the factors that determine left-right asymmetry?

Answer 21

-first sign of asymmetry involves the beating of cilia around the primitive node
+results in a directional current and expression of TGF-beta molecules (Nodal and Lefty-1)

-asymmetrical current occurs between 2 and 6 somite stage in mouse

Question 22

How do nodal and lefty-1 for left-right asymmetry? What additional factors are used?

Answer 22

• nodal: symmetry breaking molecule in the left side of the embryo, swept to left side of primitive node by ciliary current, stimulates gene pathways through Pitx-2
• lefty-1: left side of the primitive streak, blocks diffusion of molecules to the right side
• Shh, retinoic acid, FGF-8