Lecture 2: Neuronal Development (cont'd) and Axon Guidance Flashcards
What is Reelin?
a gene that when encoded, responsible for neuronal migration during development. Expressed in Cajal - Retzius cells.
What happens in a reelin mutation?
Reelin is expressed in the Cajal - Reztius cells located towards the pial surface. The neurons do not wrap arounf the radial glia. Therefore, no reelin, cells in ventricular zone do not migrate up and layers are inverted.
What is the purpose of notch signaling?
Notch signaling helps give rise the neuroblast and drives cell differences. Present in proneural cluster cells.
What happens in the neuroblast?
The cell in the proneural cluster with the most Asc will become the neuroblast, inhibiting the other cluster of cells remain where they are. The neuroblast will migrate inside. The signal is local and inhibitory. Notch signaling facilitates this process.
What is the purpose of Aschaete - scute?
Aschaete - scute (Asc) is present in drosophila proneural cluster cells. Helps with the creation of the neuroblast.
A gene a part of notch signaling. If absent, no nerve cells.
Describe notch signaling.
- Asc is translated first, protein is created and gives rise to DELTA.
- Delta, membrane bound ligand, binds to NOTCH receptor on the receiving cell.
- NOTCH cleaves off, enters the nucleus and binds to ENHANCER OF SPLIT.
- EOS binds to ASC. ASC is now inhibited and slows down, leading to less transcription of ASC protein.
- Because ASC slows down, delta is not being produced and cannot bind to notch on the other cell.
One cell ends up with more ASC than the other, making it the neuroblast.
What if NOTCH is mutated?
The inhibitory pathway will be gone. You’ll have too much ASC, too many neuroblasts, and too many neurons.
What if Asc is mutated?
No neuroblasts because Asc is needed in neural cluster. No neurons.
What if Enhancer of Split is mutated?
EOS inhibits Asc, if not present, more Asc means more excess neurons.
What if there is a mutation of delta?
There would be no notch signaling but too much Asc, creating more neural cluster cells and too many neurons.
What is interkinetic migration?
Involves radial glia cells. The way nucleus migrates along the progenitor glial cells
The nuclei migrate up to the basal section as they progress through the cell cycle.
What are the molecules involved with migration along the glial cells?
Reelin and Doublecortin (DBX)
What happens in doublecortin mutation?
Doublecortin is expressed in the neurons migrating and is needed in microtubule movement. double cortex layers, misplaced cells. Doesn’t follow typical migration pattern.
What other ways do cells migrate to cortex to become neurons?
From the neural crest. Neural crest cells do not rely on glial migration or tangential migration, rely on free migration.
How does cell fate get determined in crest cells?
Transcription factor expression. Some are built in with the ability to change based on what the target is. A neuron might have the ability to secrete norepinephrine or AcH based on where they target.
What happens to motor neurons over time?
We can observe less motor neurons as time passes with development.
What experiment can show you what happens to motor neurons over time and the way they survive?
Neurotrophic Factor Hypothesis Experiment:
A. Remove the limb during development so that the target muscle could not be innervated by motor neuron. There will be an increase in motor neuron death present at spinal cord at the side where the limb was removed.
B. When you add an additional limb bud to the embryo, more motor neurons survived.
C. When the leg was paralyzed, more motor neurons are rescued. Paralyzing the muscle blocks electrical activity in the muscle. This also led to more motor neurons surviving.
Describe Neurotropic Factor Hypothesis.
The target of innervation releases a limited amount to neurotropin to neuron, which is essential for the neuron’s survival. Aids in determining the correct number of neurons.
Describe neurotrophic factors
Nerve growth factor (NGF), Brain derived neurotrophic factor (BDNF), and neurotrophin -3 (NT-3) all bind to a transmembrane tyrosine kinase receptor (Trk). p75 receptor can bind with all three neurtrophins. Neurotrophic factors delay programmed cell death.
How do cell dies?
Apoptosis is programmed cell death. If the cell does not receive the right signal, it will die based of of preprogrammed instructions. Apoptosis appears to be the neuron’s default state. This process is mediated by the protein capases.
What are the pathways in which cells can die?
Extrinsically and intrinsically (intracellular events).
What are the four stages of neuronal growth?
Lamellipodia formation, neurite formation, neurite forms axon, and other neurites become dendrites.
What is the purpose of lamellipodia?
Composed of actin filaments and are necessary for cell migration, as it is responsible for cell mobility.
What are the molecules responsible for axon and dendritic growth, respectively?
Tau protein localized in axon and MAP2 protein in dendrites (SAD Kinases).