Week 5 Flashcards
How was progenitor development observed in vivo vs. in vitro?
What techniques were used?
In vivo:
- Lineage tracing using retrovirus containing LacZ gene that encodes beta-galactosidase
In vitro:
- Culturing of progenitor cells and use of cell markers
How does birth date influence identity?
What is the mechanism called that modulates this?
- The exact time that a neuron differentiates influences the type of neural cell it produces
- Example: the ventral hindbrain motor neuron progenitor domain:
Early: Visceral motor neurons
Late: Serotonergic neurons
The mechanism = Temporal switch
How is the process of temporal switching ordered in time in drosophila?
The order is precisely reflected in the sequence of T.F genes that get expressed in ganglion mother cells AS THEY DIVIDE
(The transcription factors change every division. These act as a time stamp to when they were born)
In drosophila, what is the order of T.Fs produced by the GMC from earliest to latest?
GMC-1 = Hunchback (high)
GMC-2 = Hunchback (low)
GMC-3 = Kruppel
GMC-4 = pdm-1
GMC-5 = castor
Which one is true when discussing the temporal sequence in neuroblasts?
a) The temporal sequence depends on the position of the neuroblast
b) Temporal sequence does not affect neuroblast differentiation
c) The same temporal sequence is found in all neuroblasts, no matter their location in the segment
d) The temporal sequence is not mediated by T.Fs
C
What is the molecular switch mechanism in drosophila?
Occurs due to the sequential activation of T.Fs but the exact mechanism is not yet known.
The Hunchback-Kruppel switch has been found to be due to a cell division counter/clock mechanism, but the others weren’t
In Vertebrates, the mechanism is much less well known, although some homologues of T.Fs have been identified
Temporal sequence of neuron production forms a spatial arrangement of neurons due to the act of division.
Why is this important in the mammalian brain?
How does it work?
- Forms layers (lamination) (at least 6)
- Neurons have connections both between and among layers
- Allows for more complex wiring of the the cortex
- These cortical lamina are formed from an INSIDE-OUT manner over time (opposite of drosophila)
- Newly born neurons migrate out towards the upper layer before differentiating!
When is cortical neuron fate determined? Are the neurons just migrating and responding to signals in each layer?
No - fate is decided BEFORE migration
This is backed up as migrating cells are already expressing precursors identical to the ones expressed by cells in the layer they are migrating to
What are the 4 types of neurons and where are they found in insects and vertebrates? (Hint - polar)
Multipolar:
- Dendrites off the soma
Insects - Type II sensory neurons
Vertebrates - Motor neurons, interneurons
Unipolar:
- Dendrites off the axon
Insects - Motor neurons, interneurons
Vertebrates - -
Bipolar:
- Dendrites extend beyond soma
Insects - Type I sensory neurons
Vertebrates - Olfactory neurons
Pseudounipolar:
- Soma is extended away from the axon
Insects - -
Vertebrates - Sensory neurons, trigeminal neurons
Describe the structure of axons
How do axons differ in structure to dendrites?
- Rigid core of aligned microtubules (with microtubule associated proteins (MAPs))
- Surrounded by a gel of actin filaments
- Actin filaments composed of actin subunits
- Microtubules are cylinders of alpha-beta tubulin dimers
Dendrites are similar to axons but have not so well aligned microtubules. The have different MAPs
Dendrites and axons have different MAPs. Which have which?
a) MAP1B
b) MAP2
c) Tau
a) Axon
b) Dendrite
c) Axon
Describe the structure of the growth cone
- A spikey ball at the end of a growing axon
- Spikes are called filopodia and contain collections of growing actin filaments
- Microtubules follow close behind, extending into the growth cone itself and binding to the rear of the extending actin filaments in the filopodia
- Filopodia contain receptors sensitive to external signals
Transport within the axon is important for cell growth as the growth cone needs stuff basically.
How does intracellular transport work in the axon (specific proteins involved)?
- Kinesin and Dynein function as molecular motors, travelling along microtubules
- Cargoes include PIP3 vesicles, tubulin dimer, tubulin mRNA etc
Growth cones respond to a huge variety of signals that influence outgrowth such as morphogens, ECM factors and other axons
These signals can be transduced in multiple ways also, such as through PAR complexes, PIP3 and small G protein signalling.
Tough one but what specific G proteins are involved in
a) Positive signalling
b) Negative signalling
c) Response to growth factors (different to + signal)
and what do they result in?
a) Rac - Elongation and lamellipodia
b)
- Rho - Stalling or retraction
- Cdc42 - Initial outgrowth, branching
c) Ras - Alterations in gene expression / PIP3 production –> Elongation
See Diagram in notes for how these G-proteins interact with each other
2 examples of effector proteins are Arp2/3 and Cofilin. What do they do to actin filaments?
Arp2/3 - Promotes branching of actin filaments
Cofilin severs actin filaments creating more barbed ends for extension (increase gel)
