Lecture 9- Patterning of the Nervous System: Dorsal-Ventral patterning Flashcards
When does dorsal ventral patterning occur?
- early in in neurogenesis
- as the neural plate starts to fold, it marks the beginning of dorsal ventral patterning
- picture: 23-24 hr old chick embryo, closure of neural tube: even here have specified dorsal and ventral patterning, not yet commited though, as dividing neuroepthilial cells are still active

What is the structure of the neural tube along the dorsal-ventral axis?
- neural tube with underlying notochord forms
- by the time the neural tube closes there is a clear dorsal-ventral pattern
-the node extends under and becomes the notochord, this influences the cells close to it, midline cells= to become floor plate
(dorsal)
-the neural fold cells= also influenced by surrounding ectoderm (ventral)

What is the development of the node into the notochord over time in a mouse embryo?
- early on (early streak stage) it is the gastrula organiser (GO)
- mid-streak stage it is the node
- it later extends anteriorally and becomes the notochord
(red is the notochord)

Does the mouse embryo turn during development?
- yes
- the picture shows embryo 8.5 (left) and 9.5 (right)

What is this?

- saggital section through a 9.5 days old mouse embryo
- shows the dorsal-ventral patterning occuring
- can see the influence of morphogens in both the dorsal and ventral region
What are the primary organizers in dorsal-ventral patterning?
- Overlying Ectoderm
- Underlying notochord

What does the Overlying Ectoderm secrete?
- dorsalizing morphogens
- BMPs, FGF, Wnts

What does the Underlying Notochord secrete?
- ventralizing morphogens
- Sonic hedgehog (Shh)

What is the specification of neural crest cells in the dorsal neural tube mediated by?
-mediated by BMP and Wnt signals from surrounding ectoderm
How do neural crest cells arise?
- neural crest cells are specified in the neuroepithelium
- go from being neuroectoderm to mesenchyme-like cells
- delaminate from the neural tube prior to neural tube closure
- first derived from neuroepithelial cells
- arise due to Wnt and BMP signalling
- will become PNS, melanocytes, dentine structures etc.

What are the secondary organisers in dorsal-ventral patterning?
- Roof plate
- Floor plate

When do the secondary organizers appear?
-once closure of the neural tube is finished
What does the roof plate develop from and what does it secrete?
- neural tube becomes roof plate
- secretes dorsalizing BMP and Wnt morphogens

What is the floor plate derived from and what does it secrete?
- neural tube becomes floor plate
- secretes ventralizing Sonic hedgehog
- Floor plate is induced by the notochord
What is the relationship between BMP and Shh?
- BMP inhibits Shh signalling
- Shh inhibits BMP signalling
- this helps to induce the cells to be ventral or dorsal
What does BMP do?
-induces dorsal cell types and represses ventral cell types
What does sonic hedgehog induce and repress?
- induces ventral cell types and represses dorsal cell types
- very sensitive gradient system, finesse!
Why is the expression of different transcription factors important in dorsal-ventral patterning?
-the expression of different transcription factors along the dorsal-ventral neural tube gives rise to various cell types, including dorsal and ventral interneurons and motor neurons

Where in the neural tube will be different types of neurons induced (dorsal-ventral pattern)?
- have Shh being released from the floor plate and BMPs and Wnts from the roof plate, differing concentration of these will induce various neuron types
- going from the ventral (Shh, floor plate) to the dorsal side (BMP,Wnt, roof plate)
a) floor plate
b) V3 neurons
c) motor neurons
d) V2 interneurons
e) V1 interneurons
f) V0 interneurons
g) D2 interneurons
h) D1 interneurons
i) roof plate - green represents Shh, blue BMPs and Wnts

What are the two gradients most important for induction of neurons and interneurons in the neural tube?
- Gradient of Shh
- Gradient of TGF-ß family factors (BMP4, BMP7, BMP5, Dorsalin, Activin)
How is the infuence of TGF-ß family factors distributed in the neural tube?
- BMP4,BMP7,BMP5, Dorsalin and Activin are all present in the very dorsal region of the neural tube
- moving ventrally only BMP7, Dorsalin and Activin remain
- moving even further in the ventral direction only Dorsalin and Activin remain

What are the V3 neurons for?
-visual system
What is cell division like in development (short summary)?
- at first have proliferation of neuroepithelial cells within the ventricular zone of neural tube
- then have differentiation to progenitor, exit ventricular zone and migration to intermediate zone (or beyond)
- Differentiation to specific neuron or glial cell

What type of cell division is there during development?
-initially in development just symmetric division later asymmetric, more and more asymmetric as development progresses










