Ribera Embro I-III

Question 1

Zones of secondary neurogenesis

Answer 1

3 characteristics

1. Cells arise in ventricular zone
2. Relocate while still in the cell cycle (not post-mitotic)
3. Proliferate at new site

3 zones, postnatal neurogenesis happens here.

1. External granular layer - EGL. Impt for genration of granular neurons in the cerebellum (generated postnatally). Sit on dorsal surface of cerebellum, migrate down.
2. Subventricular zone - gives rise to neurons in olfactory bulb.
3. Dentate gyrus (hippocampus) - likely site of adult neurogenesis

Question 2

7. Given the ventricular zone with an apical (close to the ventricle) and a basal side, in what locations would you find the nucleus of cells in a) S phase b) G1, G0 and c) M phase?

Answer 2

a) basal side
b) intermediate
c) apical surface near the ventricle

Question 3

CNS 3 types of cell migration

Answer 3

1) radial - radial glia are the 1st cells generated, cajal cells are the second, then the remainder of the neurons and glia are generated
2) tangential - inhibitory interneurons in the cortex migrate from the lateral and medial ganglionic eminences up into the cortex (around the ventricle)
3) chain - generation of olfactory bulb neurons from cells in the subventricular zone (rostral migratory stream).

Question 4

1. Describe factors/mechanisms that determine when a cell stops dividing and begins differentiating.

Answer 4

-Perpendicular vs horizontal (continue dividing vs stop, respectively) - this is called asymmetrical division. These asymmetric divisions result in different concentrations of intracellular proteins as well (gradients established by the proximity to the ventricular zone).

Question 5

Neuron birthdate?

Answer 5

The daughter can detach its other process from the ventricular surface and cease dividing. The cell is now considered a post-mitotic neuron, with its birthdate being the last S phase. Now, neuronal differentiation begins.

Question 6

10^15 =
10^12 =
10^5 =
25K =

Answer 6

10^15 = synapses
10^12 = neurons
10^5 = starting # neurons
25k=genes

Question 7

What are the three steps in radial migration? What proteins are associated with each step?

Answer 7

get on [FLNA] - FilaminA
stay on [LIS1, DCX]
get off [reelin]

Question 8

What type of neurons undergo tangential migration?

Answer 8

Inhibitory GABA interneurons

Question 9

Where in the developing brain does chain migration occur?

Answer 9

Neuronal precursor cells (that will become olfactory bulb neurons) move from the
Subventricular zone–> Rostral migratory stream–>olfactory bulb where they mature and become post-mitotic.

Question 10

What is the function of neurotrophic molecules? What are some examples of specific molecules? What class of receptors bind these neurotrophic compounds.

Answer 10

Neurotrophic molecules are NOT guidance molecules, they simply create an environment conducive to neuron growth (eg avoid apoptosis; if you plate neurons in a dish with plenty of neurotrophic substance, it will grow axons all over the place).

Nerve Growth Factor (NGF) was the first discovered. Others are BDNF, and NT-3. NGF binds TrkA, BDNR binds TrkB, etc.

Question 11

What will happen to the number of neurons if the target muscle is removed? Why? What if you add targets?

Answer 11

If the target muscle is removed, the number of neurons will drop. This is probably due to the loss of neurotrophic substance, and results in neuronal apoptosis. If targets are added, the number of neurons will not drop.

Question 12

What disease state is associated with the first step in radial migration (onset, attachment to the radial glial cell)

Answer 12

Periventricular Heterotopia (PH). Due to a mutation in FLNA (FilamentA), neurons can’t “board the train.” The gene is X-linked. Male fetuses do not survive to term, females are typically affected with epilepsy and mental retardation.

Question 13

What disease(s) are associated with the second step in radial migration?

Answer 13

Lissencephaly Type I and Double cortex syndrome (DCX). Lissencephaly (smooth brain) is due to a mutation in LIS1, located on chromosome 17; heterozygotes show severe mental retardation and epilepsy.

DCX in males presents with the same phenotype as Lissencephaly. Females are less severely affected, as the gene is located on the X chromosome.

Both proteins are thought to regulate microtubule polymerization.

Question 14

What disease state is associated with the final step in radial migration?

Answer 14

Lissencephaly with cerebellar hypoplasia (LCH). The majority of cases are due to mutations in the human “reeler” gene (cerebellar involvement causes gait anomalies, hence the nomenclature).

Reelin is made by Cajal-Retzius cells, which reside in the marginal zone (near the pia).

Question 15

What are two examples of long-range guidance molecules? Are they repulsive or attractive?

Answer 15

Netrins (repulsive OR attractive, depends on the receptor expressed in the growth cone, based on cAMP expression levels.)

Semaphorins (repulsive)

Question 16

What are some examples of short-range guidance molecules? (list by attractive/repulsive) Where are they located?

Answer 16

Attractive (cell surface): cadherins, CAMs
Attractive (ECM): collagen, laminin, fibronectin proteoglycans

Repulsive (cell surface): semaphorins (can also be long-distance if they are cleaved from the membrane), ephrins
Repulsive (ECM): tenascin

Question 17

What biochemical series of events allows neurons to form decussations (eg cross the midline?)

Answer 17

Netrins are responsible. Remember that these can be repulsive or attractive, depending on the environment in the growth cone. cAMP levels determine the interpretation of the signal.

The commisural interneurons will first be attracted towards the midline, then continue past it, which requires a complex interpretation of chemical gradients.

Question 18

15. Describe neural crest cells and the neuronal populations do they give rise to.

Answer 18

Neural crest cells give rise to the peripheral nervous system (in addition to pigment, cartilage, etc.). They migrate WITHOUT a cytoskeletal network (ie no radial glia).

Integrins on the cell membrane of NC cells interact with laminin and fibronetcin, which are permissive factors. Cadherins are expressed when the NC cells reach their final destination.

Question 19

10. Define preplate and subplate with respect to neuronal migration. Which part of the brain is forming as a result of these structures? Which type of migration do they use.

Answer 19

The subplate is a precursor to the preplate, and plays a pioneering role in the radial migration of cortical cells before dying out. The preplate differentiates into the marginal zone and the cortical plate.

Question 20

22. Describe when myelination occurs

Answer 20

Postnatally.

Question 21

23. Describe how Autism Spectrum Disorder (ASD) affects normal development. What are 3 broad categories of genes involved? Give a specific example of each.

Answer 21

ASD - 3 broad categories of genes
1. Genes that affect transcription (MeCP2, x-linked, most males die prenatally, gives rise to Rett syndrome. Protein only expressed in post-mitotic cells.)

2. Genes that affect protein stability (Angelman syndrome. UBE3a [ubiquitin ligase] which is present at the synapse. It ubiquitinates a protein important for the internalization of AMPA receptors. Mutation of this gene leads to loss of AMPA receptors at the synapse.)
3. Genes that affect synaptic proteins (specifically the activity-dependent regulation of synapses eg Ca++ channel proteins, neurexin/neuroligand/SHANK)

Question 22

24. Know when myelination occurs.

Answer 22

Begins prenatally in the brain, BUT the majority occurs postnatally.

Question 23

25. Describe two ways in which function of GABA receptors is developmentally regulated.

Answer 23

During development, GABA is often an excitatory neurotransmitter, due to the presence of a KCC2 channel that increases the Cl- concentration inside the cell. Thus, stimulation by GABA can DEpolarize and is excitatory in the embryo.

Question 24

26. Define synapse elimination and discuss when and where it occurs

Answer 24

Synapse elimination occurs POSTnatally and is NOT caused by apoptosis! Activity dependent.

We see this phenomenon in the cerebellar Purkinje fibers, where multiple “climbing fibers” initially innervate each fiber (polyneuronal innervation), but synapse elimination removes all but one.

Also seen in the NMJ, the transition from polyneuronal innervation to single innervation.

Question 25

Describe how Down’s syndrome differs from normal development.

Answer 25

Dendritic spines abnormally thin and short (don’t thicken)

Question 26

In addition to neurotrophins, what adhesion molecules are involved in synapse formation?

Answer 26

1) Neurexins (PRE) and Neuroligands (post) - neurexins interact with Ca++ channels (areas of high activity) and neuroligands interact with proteins in the postsynaptic density
2) Cadherins - Ca dependent adherence molecules. Mark the outer margin of the functional zone in the mature synapse.
3) ephrins are also involved (no more info given)

Question 27

Where is the dentate gyrus located?

Answer 27

In the hippocampus. It seems that cells here undergo a similar migration as the olfactory neurons that travel in the rostral migratory stream.

However, the dentate gyrus is one of the 3 secondary zones of neurogenesis, so these cells will remain mitotic. (The other two zones are the External Granular Layer and the Subventricular Zone).