Lecture 15 Flashcards
Below are a list of regions contained in the ventral neural tube that are formed as a result of sonic hedgehog signalling, put them in order of dorsal to ventral. A - floor plate, B - Motor neuron progenitor, C - ventral progenitor 1, D - ventral progenitor 0, E - ventral progenitor 3, F - ventral progenitor 2
d, c, f, b, e, a
In vertebrates sonic hedgehog is expressed in the axial mesoderm and the floor plate simultaneously, T or F
F – sonic hedgehog is first expressed in the notochord and prechordal mesoderm and then induces its own expression in the floor plate of the ventral neural tube
What is the role of Pax3, 6, 7 and Lim1
Cause neural tube progenitors to acquire dorsal identities
Sonic hedgehog patterns the ventral portion of the developing neural tube, T or F
T
BMPs and Wnts released by the roof plate cells diffuse into dorsal neural tube and induce expression of which set of transcription factors
Pax6, 7, 3 and Lim1
What neuronal fates with the most ventral cells in the neural tube adopt and which transcription factors are involved in this
The most ventral neurons will become motor neurons of the spinal cord reflex arcs and will begin to express Olig2 and Nkx6.1
Sonic hedgehog acts as a morphogen to regulate transcription factor expression by directly inducing their expression, T or F
F – sonic hedgehog activates transcription factor expression through de-repression
BMP signalling is responsible for patterning the dorsal neural tube. How is a BMP gradient established dorsally in the neural tube
BMPs from the surface ectoderm induce their own expression in a dorsal group of cells called the roof place cells. BMPs then establish a dorsal morphogen gradient
Which gene is expressed most dorsally in the neural tube having initially been expressed throughout the axis prior to sonic hedgehog expression
Pax6
Explain how sonic hedgehog signalling leads to transcription factor expression in the ventral neural tube
Genes in the neural tube are initially expressed throughout the structure due to Wnt and BMP signalling. Shh then suppresses their expression and confines them to the dorsal part of the spinal cord. These genes are differentially sensitive to Shh (Pax7, Dbx1, Dbx2, Irx3) and are referred to as class 1 genes, transcription factors which act to repress other genes. As class 1 genes are transcriptionally repressed by Shh class 2 genes are turned on because they are de-repressed (Nkx6.1, Nkx2.2, Olig2)
What factors help determine which cell types neural progenitors differentiate into
Position or origin of neural crest cells, time of generation and migratory pathway
Give examples of class 2 genes switched on by sonic hedgehog signalling
Nkx6.1, Nkx2.2, Olig2
All of the neural plate border cells form neural crest cells, T or F
F – some neural plate border cells are retained and form roof plate cells
What structures does the neural plate border give rise to
Peripheral nervous system, roof plate cells
What will the most dorsal neurons in the neural tube give rise to
These neurons will become the commissural sensory relay neurons that relay information from the spinal cord to the brain
FoxA2 is a transcription factor characteristic of the floor plate, T or F
T
GliA is an example of a gene that is switched on by sonic hedgehog. What is the role of GliA in patterning the neural tube and how is the mechanism of its activation different to most other genes switched on by sonic hedgehog
GliA is a transcription factor that defines the floor plate and turns on the expression of other characteristic floor plate genes. It, along with a few other genes, is directly activated by very high concentrations of sonic hedgehog
How do experiments looking at the expression of sonic hedgehog protein differ from those visualising mRNA
Immunohistochemistry experiments using antibodies to identify where sonic hedgehog is localised does show these round and triangular regions representing the axial mesoderm and floor plate. However, the expression is punctuate and more diffuse indicating a morphogen gradient. Sonic hedgehog is highest at the axial mesoderm and floor plate and decreases dorsally throughout the neural tube
Give examples of class 1 genes transcriptionally repressed by sonic hedgehog
Pax7, Dbx1, Dbx2, Irx3
How many different progenitor domains are established along the DV axis that give rise to different neuronal populations
10-12
What transcription factors are characteristic of motor neuron fates
Olig2 and Nkx6.1
What cell types do the neural plate border cells form
Neural crest cells
What is the roles of roof plate cells
Important in the final step of neurulation and dorsal neural tube patterning
Explain the differences between experiments visualising sonic hedgehog mRNA
In situ hybridisation experiments aimed to visualise where sonic hedgehog mRNA is transcribed shows a clear define pattern. Initially this shows a clearly defined, round expression pattern indicating its expression in the notochord/prechordal mesoderm. Later experiments would indicate another clearly defined triangular region of expression lying dorsally to the notochord and in the ventral neural tube. This identifies the newly induced sonic hedgehog expression by the floor plate.
What happens later in development as cells of the neural tube begin to differentiate
As progenitor cells differentiate into neurons that differentiating progeny move laterally so that mature neurons are present in the mantle zone. The other daughters remain as progenitors near the lumen of the neural tube
At what chick embryonic stage is sonic hedgehog first expressed at and what does the correspond to
Sonic hedgehog is first expressed in the axial mesoderm at stage 4 where the primitive streak has reached its maximum extension
What is the name of the border that forms at the neural-ectoderm boundary
Neural plate border
How does experimental evidence indicate sonic hedgehog is a morphogen
Immunohistochemistry to visualise where sonic hedgehog expressed reveals an expression pattern that indicates a morphogen gradient
What do the middle neurons between the most dorsal and ventral progenitors become
These will become interneurons that mediate interactions between the other neurons
What transcription factors upregulated by NBP and Wnt cause proliferation and multipotency and characterise neural crest cells
C-Myc, Id and Snail
What molecules are attached to antibodies to enable you to visualise proteins in a cell/tissue
Fluorochromes
Genes encoding different transcription factors begin to be transcribed and translated in different cells along the D-V axis in a precise spatial manner, T or F
T
Which structure begin to express sonic hedgehog in the axial mesoderm as is extends forwards
Prechordal mesoderm, notochord
What causes the formation of this border at the neural-ectoderm boundary
Cells have received an intermediate level of BMP and have begun to go down but not fully towards a neural fate
Cells of the axial mesoderm and floor plate are responsible for ventralising the neural tube, T or F
T
The neural plate cells are a neuronal population of cells, T or F
F – they are a glial population
Dbx 1 and dbx2 are expressed in which regions of the ventral neural tube
Ventral progenitors 0, 1 and 2
The early border begins to express msx which acts with Wnt and FGF to turn on transcription factors Pax3, Zic1 and Pax7, T or F
T
What other key signalling pathway is active in the dorsal neural tube and is thought to maintain proliferation
Wnt signalling
