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Mursizzle
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What is the area identity?
Brain is separated into many domains
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Intrinsic
Cell decides what its going to do to drive cell fate
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Extrinsic
- Cell isnt completely isolated
- Responds to external factors
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How is the V1/V2 layer distinguishable?
By the cytoarchitecture
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Where do the extra cell layers start to form in the V1 cortex?
Cell layers start to form at 4th layer
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Name the cortices in the brain from anterior to posterior.
- Motor cortex
- Somatosensory cortex
- Auditory cortex
- Visual cortex
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Name the cortices in the brain from posterior to anterior.
- Visual cortex
- Auditory cortex
- Somatosensory cortex
- Motor cortex
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What kind of input do distinct ares of neocortex receive?
Different thalamocortical axon (TCA) inputs
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What does TCA stand for?
Thalamocortical axon
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How are the identities of neocortex areas determined/specified?
Independently of axonal input from TCA
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How do all signals, besides olfactory, reach the cortex?
By relay of the thalamus (TCA)
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Which sensory signals reach the cortex by relay of the thalamus?
All but olfactory
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What are the two transcription factors expressed in the developing cortex in mice?
Emx2 and Pax6
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What are Pax6 and Emx2?
- Transcription factors that help drive AP cell fates when expressed
- Intrinsic factors
- (but external signals exist too)
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How are the transcription factors expressed in the cortex of mice?
In gradients
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What can you say if you see one gradient?
Chances are there is an opposing gradient
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How are Emx2 and Pax6 expressed?
In opposite rostral-caudal gradients
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What do Emx2 and Pax6 do?
Help dictate regional specificity
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Where is pax6 expressed most? Least?
- Most- Anteriorly (rostrally)
- Least- Posteriorly (caudally)
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Where is emx2 expressed most? Least?
- Most- Posteriorly (caudally)
- Least- Anteriorly (rostrally)
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What happens when theres a mutation in pax6?
- Causes posteriorization (expansion of the posterior)
- Boundary of posterior marker shifts anteriorly
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What happens when theres a mutation in emx2?
- Causes anteriorization (expansion of the anterior)
- Boundary of anterior marker shifts posteriorly
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What is the hypothesis of the roles of Emx2 and Pax6?
They play a role in establishing areal cell fates along the AP axis
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What is FGF?
- Fibroblast growth factor
- Influences areal patterning
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How is FGF expressed in the cortex?
- In a gradient
- High anterior, low posterior
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What happens when ectopic FGF8 is expressed in the anterior of the cortex?
- Causes posterior shift of cortical domains
- Anteriorization
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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
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What is the path of sensory signals when mouse whiskers bend?
- Trigeminal nucleus
- Brain stem
- Dorsal thalamus (VP)
- Neocortex
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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
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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
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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
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What are the two principle neuronal types?
Excitatory (glutamatergic) and inhibitory (GABAergic) neurons
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Where do excitatory neurons come from?
- Progenitors in the dorsal cortical ventricular zone
- Migrate radially to occupy the future vesicular cortex
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What controls the excitatory neurons?
Neurogenin 1 and 2
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Where do inhibitory neurons come from?
- Progenitors in the ventral ganglionic eminences
- Migrate dorsally to become interneurons
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What controls the inhibitory cells?
Mash1
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What are neurogenin 1-2 and mash1?
Basic helix-loop-helix (bHLH) transcription factors that dictate the nt phenotypes that cells release
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How many principle layers are there in the audlt cortex?
6
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Which two layers are grouped together for simplicity's sake b/c they're hard to distinguish?
Layer 2/3
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What kind of cells do the 6 cortical layers consist of?
Excitatory pyramidal neurons w/ different roles
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What are the 5 layers/areas where cells migrate and develop from top to bottom?
- Marginal zone
- Cortical plate
- Subplate
- Intermediate zone
- Ventricular zone
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Where do cortex layers 2-6 form?
In the developing cortical plate
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What's another name for the progenitor cells starting in the ventricular zone?
Radial glia
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Where are the dividing progenitor cells located?
Ventricular zone
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What are radial glia cells?
Progenitor cells
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Where are radial glia cells located?
- Extends from the ventricular zone to the marginal zone
- Entire length of the early cortex
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What happens in the intermediate zone?
Post mitotic cells migrate upward
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How do post mitotic cells migrate up to the cortical plate?
Along the scaffold of radial glia
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Where does differentiation of post-mitotic cells finish?
At the cortical plate
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When is a cell considered "born"?
When the cell last divides
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How do progenitor cells divide?
Symmetrically or asymmetrically
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What influences the fates of dividing progenitor cells?
The plane of division with respect to the epithelial surface of the ventricular zone
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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)
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When does asymmetric division occur?
When mitotic spindle lines up perpendicular to the epithelial surface of the ventricular zone
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How does asymmetric division occur?
Cell divides upon the cleavage plane, thats parallel to the epithelial surface
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What happens during symmetric division?
Progenitor gives rise to two new progenitor cells
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When does symmetric division occur?
When the mitotic spindle lines up parallel to the epithelial surface of the ventricular zone
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How does symmetric division occur?
Cells divide upon the cleavage plane, thats perpendicular to the epithelial surface
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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
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What are examples of cell-fate determining proteins?
Notch and numb (which inhibits notch)
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