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138 Lectures 11-14
Terms in this set (42)
The Nieuwkoop Center patterns ______________ using ___________
the mesoderm D/V axis, using a Nodal gradient
Is any of the early frog gastrula differentiated?
Yeah, the Nieuwkoop center and Spemann organizer b/c transplanting them causes them to retain their cell fate and induce surrounding cells to be other things (but the rest of the embryo is unspecified AF)
What cell movement processes involve production of the Nieuwkoop Center?
Involution of the future endoderm and mesoderm to be under the ectoderm and convergent extension of dorsal cells to help form dorsal lip
What does the Spemann organizer induce and how?
It induces dorsal (neural) ectoderm using BMP antagonists like chordin, noggin, and follistatin (dude i s2g if you don't know this shit u gon fail and then dad will have something to replace the math grade DON'T LET THAT HAPPEN)
How was the signal of the Spemann organizer discovered? What happens if you get rid of it?
Co-cultured it with ectoderm, separated by nitrocellulose filter and ectoderm still got neural-y, so its secreted
cDNA libraries showed it was chordin/noggin/follistatin (thank you based De Robertis) - MO's vs them means no neural stuff, MO's vs BMP means ALL NEURAL MAXIMUM OVERBRAIN
How does the Xenopus embryo get its A/P axis (structure involved, not signals)?
Spemann organizer does SOMETHING, involving Hox genes -older organizer transplant induces more posterior structures instead of a whole A/P axis
What signals pattern the Xenopus A/P axis?
Wnt signaling posteriorizes the embryo, Spemann organizer makes Wnt antagonists to induce anterior parts of the embryo
How the frick frack diddly dack does Lateral Inhibition work?
Secreted Delta binds Notch receptor, which signals a downregulation of neurogenin signaling, which causes less Delta to be formed, which lowers Notch signaling, etc
One lucky cell gets some random extra Delta production, it inhibits other cells more and frees itself to differentiate.
Main differences between Birds/Mammals and Frogs in development?
1. Flat sheet vs sphere
2. Movement specifies germ layers vs specified pre-movement
3. Ingression to internalize mesoderm instead of involution
How does Bird/Mammal gastrulation begin?
Formation of primitive streak due to Wnt signaling at Posterior Marginal Zone inducing Nodal expression in adjacent cells, which combines with FGF from other adjacent cells to induce mesoderm
What does the movement of the primitive streak do?
Specify endoderm and mesoderm as the cells that ingress through it, induce convergent extension in developing embryo
What is the Posterior Marginal Zone analogous to in the frog? Why?
The Nieuwkoop center, because:
1) it induces the mesoderm and 2) transplanting it causes a new axis
What's the Node? What does it do?
Highest Nodal expression on anterior end of primitive streak, starts to turn around (more convergent extension) and go back to the posterior end and secrete chordin
What cells become the somites?
Paraxial mesoderm: mesoderm that has migrated just outside the range of the notochord (which is the most dorsal mesoderm tissue)
What is the Node analogous to in the frog? Why? Main difference?
The Spemann organizer, because
1) it induces ectoderm, 2) transplantation causes a new axis and 3) older nodes induce more posterior structures (holla at me, Hox genes) BUT! Node proliferates, Spemann organizer does not
What are the somites differentiated into?
myotome, dermatome, and sclerotome
What process causes mesoderm to become somites?
MET of ingressed cells (which had gone EMT)
Paraxial mesoderm rotation results?
Somitic structures were reversed, meaning that there is an older signal that patterns the eventual A/P axis, but still differentiated in anterior to posterior order, meaning that there is an external signal controlling somite differentiation
How is somite differentiation timing controlled?
Clock-wavefront: FGF secretion from regressing Node causes somites to form anterior to posterior, then pulses of - feedback'd Notch/Dll inducing Mesp2 which blocks Notch signaling until it degrades
What controls which structures the paraxial mesoderm becomes?
Hox genes ofc
What is the neural tube patterned into on the A/P axis?
How is the hindbrain separated, what do these areas become, and what patterns it?
Separated into rhombomeres which become cranial nerves, and patterned by Hox genes (which may induce different cadheren expression)
How are the fore/midbrain patterned?
Patterned by FGF8 gradients from the Anterior Neural Ridge (ANR) and midbrain-hindbrain boundary (MHB)
CNS D/V axis (along spine) is patterned how?
Neural tube has opposing gradients of Shh (ventral) from the floorplate and mesoderm and BMP (dorsal) from the epidermis-adjacent ectoderm
CNS Apical/Basal axis is patterned how?
Neuroblasts migrate from apical (lumen) side of the neural tube to the basal (edges) side to make a multilayered brain cortex
How are different types of neurons induced in the brain?
Migration from the ventricular zone (VZ) to the basal part of the cell, different times = different neurons differentiated due to floorplate and intrinsic signaling
How do neural stem cells control timing of differentiation?
Lateral inhibition! Make more Delta=GTFO, make more Notch receptor=stay in mommy's basement (the VZ) forever
What cellular structures function in neuronal growth?
Lamellipodia - Flat sheet extensions that use MT's
Filopodia - Weird pointy things sticking out with MF's
All make up the Growth Cone
What controls neuronal growth's directionality? What type of signals does this give?
ECM interactions with neuron integrins, eg laminin=good, collagen=bad
ECM is permissive - it doesn't attract neurons, it either repels or allows their growth
Long Range and Short Range neuron Attractive and Repulsive cues
SR Attraction = Cadherens
LR Attraction = Netrin
SR Repulsion = Ephrin
LR Repulsion = Semaphorin
Where in neural development do cadherens work as a short-range attractive cue? (2)
During Apical/Basal development, radial glia attractions to migrating neuroblasts
Getting photoreceptors to move towards the tectum
How do commissural neurons work get to the brain?
Start dorsal, move to floorplate due to netrin signaling, then Robo3 stops blocking Robo1/2 to allow the neurons to become sensitive to Slit and also the semaphorin receptor starts getting expressed somehow. This stops the neuron from staying at the floorplate (Slit) and from going back dorsally (semaphorin)
How were commissural neuron attractive signals found?
Explant floorplate, commissural neurons grow to it from far away, therefore it's a long-range attractive cues
cDNA libraries ID'd netrin
Where are short-range repulsive cues found in neural development?
Ephrin/EphA signaling in the tectum
How does Ephrin work in patterning neurons?
Photoreceptors reach from the retina to the tectum/superior colliculus
PhotoR's express EphA gradient from nasal to temporal, tectum expresses mirrored gradient of ephrin from anterior to posterior, allows for point to point correspondence of photoR's
Which end of the tectum do photoreceptors migrate towards?
The anterior end
What experiment showed retinotectal mapping to be ultra precise?
Rotate frog retina 180 degrees, photoR's still went to the correct places
What experiment discovered the retinotectal signal?
Explant retina and tectum, saw that ganglia only grew towards the anterior parts of the tectum
A repulsive signal because the ganglia near the posterior end didn't grow at all and collapsed
What part of the embryo becomes the neural crest cells
The top of the neural tube, which has medium BMP signaling (up to the very anterior part of the embryo)
What do neural crest cells become (4)?
Dorsal root ganglia
all bone mesenchyme (including gums and teeth)
How do neural crest cells begin specification?
EMT from neural tube via downregulation of N-cadherin.
How is neural crest cell differentiation controlled?
They migrate over somites in streams
Only go over anterior end because posterior end makes ephrins
KO ephrin means NCC streams and structures all messed up
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