02-03: Nervous System Induction Flashcards
What are the steps of the formation of the notochord?
1- Cellular precursors of the notochord migrate ANTERIORLY and then are left behind as a rodlike aggregation as the primitive streak regresses
2- Notochordal cells fuse with flanking endodermal cells
3- Temporarily form a neutrenteric canal
4- Notochord cells separate from the endoderm
5- Aggregate to form a solid definitive notochord
Which layer invaginated through the primitive streak?
mesoderm
Which layer is continuous with the ectoderm of the amnion?
ectoderm
Which layer is lacking at the oropharyngeal plate?
mesoderm
What are some of the inductive functions of the notochord?
- Formation of axial structures
- 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
What is a signal that is used in the notochord’s formation of many axial structures?
Shh
What are 2 signals that are involved in the notochord’s induction of overlying ectoderm conversion to neural ectoderm?
- Noggin
- Chordin
What are 2 transcription factors that are involved in the notochord’s induction of overlying ectoderm conversion to neural ectoderm?
- Foxa-2
- Goosecoid
What is also referred to as the head organizer?
prechordal plate
What forms the prechordal plate?
early cells that pass through the primitive node
What is the prechordal plate a source of signals for?
- Shh (involved in the ventral patterning of the forebrain)
- Survival of neural crest cells that emigrate (move away) from the early forebrain
What does Wnt3 do?
induces expression of Nodal
What does Nodal do?
- establishes a posterior signaling center which induces formation of the primitive streak
- induces primitive streak and helps to establish Left-Right symmetry
What does Noggin do?
neural inducer
What does Chrodin do?
neural inducer
What does Goosecoid do?
activates genes (chrodin & noggin)
What does Foxa-2 do?
- establishment of primitive node
- initiates notochord function
- establishes midline structures cranial to node
What does Shh do?
induces axial structures
What are the 2 experiments showing neural induction?
- Amphibian: Dorsal lip of blastopore in embryo induces a secondary embryo to form
- Mammals: Primitive node graft from one embryo induces the formation of a secondary neural tube in another embryo
What is the notochord a primary inducer of?
formation of neuroectoderm
What is determination?
- a cell or part of an ambryo becomes restricted to a given developmental pathway
- a cell becomes committed to a specific cell line
**precedes differentiation
What is differentiation?
a complex of changes involved in the progressive specialization of structure and function
**resulting in the formation of luxury molecules
What are 5 examples of left-Right Asymmetry?
- heart
- looping of gut
- liver
- spleen
- lung lobation
What is the first sign of asymmetry?
the beating of cilia around the primitive node»_space; causes a directional current and expression of TGF-b molecules
What are the 2 TGF-b molecules the are expressed at the beginning of asymmetry?
- Nodal [symmetry breaking molecule on L side of embryo]
- Lefty1 [L side of primitive streak]
Which somite stages does asymmetrical current occur?
between somite stage 2-6
How does Nodal help determine asymmetry?
- Swept to the L side of primitive node by ciliary current
- Stimulates multiple gene expression pathways
How does Nodal stimulate multiple gene expression pathways?
Pitx-2
How does Lefty1 help determine asymmetry?
- Expression on L side of embryo
- Blocks diffusion of molecules to the R side
What are 3 additional factors that help determine asymmetry?
- Shh
- Retinoic acid
- FGF-8
What CAMs are in the preinduced ectoderm?
N-CAM
E-cadherin
What CAM is in the ectoderm?
E-cadherin
What CAMS are in the neural tube?
N-CAM
N-cadherin
