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What is the area identity?
Brain is separated into many domains
Cell decides what its going to do to drive cell fate
- Cell isnt completely isolated
- Responds to external factors
How is the V1/V2 layer distinguishable?
By the cytoarchitecture
Where do the extra cell layers start to form in the V1 cortex?
Cell layers start to form at 4th layer
Name the cortices in the brain from anterior to posterior.
- Motor cortex
- Somatosensory cortex
- Auditory cortex
- Visual cortex
Name the cortices in the brain from posterior to anterior.
- Visual cortex
- Auditory cortex
- Somatosensory cortex
- Motor cortex
What kind of input do distinct ares of neocortex receive?
Different thalamocortical axon (TCA) inputs
What does TCA stand for?
How are the identities of neocortex areas determined/specified?
Independently of axonal input from TCA
How do all signals, besides olfactory, reach the cortex?
By relay of the thalamus (TCA)
Which sensory signals reach the cortex by relay of the thalamus?
All but olfactory
What are the two transcription factors expressed in the developing cortex in mice?
Emx2 and Pax6
What are Pax6 and Emx2?
- Transcription factors that help drive AP cell fates when expressed
- Intrinsic factors
- (but external signals exist too)
How are the transcription factors expressed in the cortex of mice?
What can you say if you see one gradient?
Chances are there is an opposing gradient
How are Emx2 and Pax6 expressed?
In opposite rostral-caudal gradients
What do Emx2 and Pax6 do?
Help dictate regional specificity
Where is pax6 expressed most? Least?
- Most- Anteriorly (rostrally)
- Least- Posteriorly (caudally)
Where is emx2 expressed most? Least?
- Most- Posteriorly (caudally)
- Least- Anteriorly (rostrally)
What happens when theres a mutation in pax6?
- Causes posteriorization (expansion of the posterior)
- Boundary of posterior marker shifts anteriorly
What happens when theres a mutation in emx2?
- Causes anteriorization (expansion of the anterior)
- Boundary of anterior marker shifts posteriorly
What is the hypothesis of the roles of Emx2 and Pax6?
They play a role in establishing areal cell fates along the AP axis
What is FGF?
- Fibroblast growth factor
- Influences areal patterning
How is FGF expressed in the cortex?
- In a gradient
- High anterior, low posterior
What happens when ectopic FGF8 is expressed in the anterior of the cortex?
- Causes posterior shift of cortical domains
What happens to the somatosensory cortex when FGF is expressed caudally? Give an example.
- Cells think they're close to the cell anteriorly
- Adopt new/different cell fate; duplicated S1 cortex
- Duplication of mouse whisker barrel field
What is the path of sensory signals when mouse whiskers bend?
- Trigeminal nucleus
- Brain stem
- Dorsal thalamus (VP)
What are all the factors that work together to pattern the motor sensory areas?
- Anterior and posterior fgf8 gradient
- Intrinsic transcription factor gradients for Emx2 and Pax6
What was the first experiment that showed that afferent/extrinsic input from thalamus also influences organization of sensory cortex?
- Transplanted visual cortex tissue of mouse into somatosensory cortex
- Wait for it to mature
- See that whisker barrel fields form visual cortex (sensory signals now help vision?)
- Even though there's intrinsic patterning in cortex, there's enough plasticity that allows remodeling
What was the second experiment that showed that afferent/extrinsic input from thalamus also influences organization of sensory cortex?
- Compared how different inputs from other auditory and visual cortex could affect patterning of developing cortex
- Removed inferior colliculus
- No signal to MGN (medial geniculate nucleus) from cochlea
- RGC from retina innervated both LGN and branched to innervate MGN
- What used to be auditory cortex now responds to visual cues
What are the two principle neuronal types?
Excitatory (glutamatergic) and inhibitory (GABAergic) neurons
Where do excitatory neurons come from?
- Progenitors in the dorsal cortical ventricular zone
- Migrate radially to occupy the future vesicular cortex
What controls the excitatory neurons?
Neurogenin 1 and 2
Where do inhibitory neurons come from?
- Progenitors in the ventral ganglionic eminences
- Migrate dorsally to become interneurons
What controls the inhibitory cells?
What are neurogenin 1-2 and mash1?
Basic helix-loop-helix (bHLH) transcription factors that dictate the nt phenotypes that cells release
How many principle layers are there in the audlt cortex?
Which two layers are grouped together for simplicity's sake b/c they're hard to distinguish?
What kind of cells do the 6 cortical layers consist of?
Excitatory pyramidal neurons w/ different roles
What are the 5 layers/areas where cells migrate and develop from top to bottom?
- Marginal zone
- Cortical plate
- Intermediate zone
- Ventricular zone
Where do cortex layers 2-6 form?
In the developing cortical plate
What's another name for the progenitor cells starting in the ventricular zone?
Where are the dividing progenitor cells located?
What are radial glia cells?
Where are radial glia cells located?
- Extends from the ventricular zone to the marginal zone
- Entire length of the early cortex
What happens in the intermediate zone?
Post mitotic cells migrate upward
How do post mitotic cells migrate up to the cortical plate?
Along the scaffold of radial glia
Where does differentiation of post-mitotic cells finish?
At the cortical plate
When is a cell considered "born"?
When the cell last divides
How do progenitor cells divide?
Symmetrically or asymmetrically
What influences the fates of dividing progenitor cells?
The plane of division with respect to the epithelial surface of the ventricular zone
What happens during asymmetric division?
Progenitor will give rise to a progenitor cell, and a neuronal precursor which will migrate on radial glia into the cortical plate (future cortex)
When does asymmetric division occur?
When mitotic spindle lines up perpendicular to the epithelial surface of the ventricular zone
How does asymmetric division occur?
Cell divides upon the cleavage plane, thats parallel to the epithelial surface
What happens during symmetric division?
Progenitor gives rise to two new progenitor cells
When does symmetric division occur?
When the mitotic spindle lines up parallel to the epithelial surface of the ventricular zone
How does symmetric division occur?
Cells divide upon the cleavage plane, thats perpendicular to the epithelial surface
Why does the orientation of the cell's cleavage plane matter with division?
- Some cell-fate determining proteins can be unevenly distributed during mitosis
- Depending on how cells divide, one cell may get all or none of that protein
- Could lead to cell-fate decision like becoming neuron
What are examples of cell-fate determining proteins?
Notch and numb (which inhibits notch)