Neurogenesis and Gliogenesis Flashcards
1
Q
where do neural progenitors come from?
A
the neuroectoderm in the neural plate
2
Q
where do neural progenitors proliferate?
A
in the neural tube
3
Q
what are the different ways in which neural progenitors can divide?
A
symmetric division: both daughter cells have the same fate
asymmetricL each daughter has a specific, different fate
4
Q
what organism has been used to look at neurogenesis?
A
the drosophila
5
Q
how is neural competence initially acquired within th eneuroectoderm?
A
a group of cells initially acquires neural competence within pro neural clusters which respond to the columnar, segmental patterning that accord within the fly embryo along the ventral portion
6
Q
from the group of neural clusterd cells, how many will be give rise to a neuronal precursor?
A
just one, the neuroblast
7
Q
what are the pro neural genes that give neural fate to the neuroblast?
A
achaete and scute
8
Q
what re achieve and scute?
A
b-HLH transcription factors
9
Q
what is the expression pattern within the neural clusters over time?
A
all the cells initially express achieve and scute but then only one, the neuroblast will eventually express it.
10
Q
how can you view the neural clusters? how does the expression change over time?
A
you can do in situ for achaete and scute and you will see that initially many cells within a cluster express them but then eventually only one will
11
Q
how did people go about finding the genes involved in the process by which only one neuroblast will give rise to the neural cell? what did they find?
A
people carried out forward genetics screens and looked for mutants that didn’t have these proneural clusters or had an enlarged nervous system due to the presence of too many neuroblasts - genes involved in lateral inhibition were involved
12
Q
what is the process by which one neuroblast of the neural clusters expresses ac and sc and turns off the expression in the others?
A
lateral inhibition
13
Q
what is lateral inhibition?
A
it is a process mediated by cell-cell communication. one cell accumulates higher levels of pro neural proteins and instructs the other adjacent cells to turn off pro neural gene expression
14
Q
what is the oscillation- stabilise theory of lateral inhibition?
A
there are transcriptional oscillations that cause fluctuations which lead to an overall different tin one cell which allows it to dominate. the initial expression of the relative genes is present at a level 2 which is unstable (the cell ants to either be at expression levels 1 or 3) this is called a bistable switch that is orientated around 1 and 3. So a cell that becomes 3 will then tell the other cells to become 1
15
Q
what are the 2 processes involved in breaking the symmetry in pro neural gene expression within the pro neural clusters?
A
a positive feedback loop of higher expression and a bistable switch
16
Q
what pathway is implicated in lateral inhibition?
A
the notch signalling pathway.
17
Q
how does the notch signalling pathway work?
A
delta is expressed in a cell which will bind to notch and cause notch to downregulate pro neural genes and then this will downregulate delta- results in one cell expressing delta and pro neural genes and the other expression notch and no pro neural genes
18
Q
what is the pathway of delta notch in the lateral inhibition of neuroblast expression thought to be?
A
proneural genes become higher in one cells, this stimulates more delta in one cell causing increased notch activate in adjacent cells meaning that they downregulate delta
19
Q
when does the first wave of neurogenesis occur in vertebrates?
A
at the neural plate stage
20
Q
in vetebrates, where are pro neural genes expressed?
A
longitudinal domains in the neural plate called proneural fields
21
Q
what are the pro neural fields?
A
the longitudinal domains in the neural plate that express pornerual genes
22
Q
how can the refinement of the neuronal precursors within the neural fields be seen in vertebrates?
A
if you do in situ for the neural genes you see that their expression becomes refined in the proneural fields
23
Q
how can you prove that notch is involved in lateral inhibition within the vertebrate?
A
you can find mutants that have knockouts for components of the notch signalling pathway and see that they have too many neuroblasts and then too many neurons- one such is mind bomb
24
Q
what is a mutant that contains a mutation in the notch signalling pathway?
A
mindbomb- too many neurons due to too many neuroblasts and no lateral inhibition
25
how can you physically manipulate the notch signalling pathway to increase the signalling of notch and increase lateral inhibition?
you can inject mRNA for the NICD and you will see using in situ that there are less neuroblast and less pro neural gene expression
26
generally, list the three things that happen in order for neural progenitors to be formed?
- initial generation of pro neural clusters from neural epithelial cells
- notch isgnalling speicifes neural progenitors from pro neural clusters
- appears consistent between drosphila and zebrafish (verts)
27
what are the 3 stages in neuron differentiation in the fly?
1. delimination
2. asymmetric cell division
3. differentiation
28
what is the process of elimination within the fly?
the neuroepithlium of the file neural tube is made from cells. These cells start to downregulate cadherins in the neuroblast and then the neuroblast migrates
29
why is asymmetric inheritance important in neurogenesis, what does it ensure?
it ensures that duringg a cell division of the neuroblast, the neuroblast maintains its dividing ability and phenotype as a neuroblast, and the daughter can become a GMC
30
along what axis do neuroblast migrate along?
they move away from the apical and migrate towards the basal end
31
how does the spindle change within the neuroblast during asymmetric division in flies?
the spindle changes orientation in order to facilitate the asymmetric inheritance which determines which daughter will be the neuroblast and which the GMC. The single changes from parallel to the apical basal axes to be being perpendicualr
32
what are the two steps in asymmetrical cell division?
- spindle change and asymmetric inheritance of cues
33
is the process that mediates asymmetrical division in flies (spindle change and asymmetric inheritance of components) conserved in vertebrates?
the single orientation does not have an affect
34
how was the role of spindle orientation in asymmetric division investigated in vertebrates?
a woman looked at whether the spindle orientation and the fates it gave rise to and she saw that the spindle can be parallel or perpendicular- it doesn't bias one towards a certain fate .
35
how was it shown that the asymmetric cell fate is determined by inheritance of cues, but that the inheritance of cues is independent from spindle orientation in zebrafish?
a woman looked at the planes of division and found there was no correlation between this and fate. But then she looked at whether the inheritance of apical or basal cues was important and she did this by labelling the basal cues with GFP. She found that whichever cell inherited this when on to be the neuron and the one which has the basal projection stays as the progenitor and develops a new apical membrane.
36
how is the mouse asymmetric division process different to the zebrafish?
in the mouse it is the apical cell that becomes the progenitor, not the neuron.
37
what are the cell intrinsic and the cell extrinsic factors that determine cell fate?
intrinsic are transcription factors exrpressed by the precursor and extrinsic are signals present in the environment
38
what is the general role of the extrinsic and intrinsic signals within a neuronal precursor?
they determine the competence of the cell to give rise to a specific cell type.
39
how is cell fate determined in the fly for neuronal precursors?
from the neuroblast moving out the epithelium, each division gives rise to a different neuronal type. the expression profile of certain transcription factors determines the fate of the cell. The time at which the divison takes place and the TF being described determine the fate. As time goes on, the cell is cycling and tells us that cell cycling control is crucial to determining cell fate. This regulation occurs through internal cell cycle clock so internal factor dependent. But there are also glial factors which also signal and determine the fate. It is the interplay- very complex.
40
what is the role of the extrinsic factors in determining neuronal precursor cell fate?
Signals present in the environment (extrinsic factors) are essential to coordinate cell cycle control and fate determination
41
what is the role of the intrinsic factors in determining neuronal precursor cell fate?
over time the expression if TFs within the cll changes and it is the combination of these Tfs which determine the competence of the cell
42
what is the ganglion mother cell?
a daughter from neuroblast division which will divide terminally to generate two post mitotic glia/neuron cells
43
what is apically localised in the neuroblast in the fly?
the par protein complex
44
what is in th e par protein complex?
Par3/ Par6/aPKC
45
what is the difference between embryonic neuroblasts and larval neuroblasts?
embryonic neuroblasts have a greater capacity to divide and generate larger lineages of postmitoic progeny , they can also grow and regain their original size after division
46
list 4 proteins that are localised to the apical side in the fly neuroblast during asymm division and hence inherited by the neuroblast
the par complex (par6, aPKC), bazooka, inscuteable
47
list 4 proteins that are localised to the basal side in the fly during asylum division and hence inherit by the GMC
Pon- Numb, Miranda, brat, prospero
48
how does prospero act on the basal side?
it can act as a Trasncriptional activator sand repressor to induce neuronal differentiation genes and repress neuroblast identity and those factors involved in cell cycle- CycA and CycE
49
what is the role of brat in the GMC?
activate Prospero
50
which and how proteins orientate the changing on the mitotic spindle in the fly?
Pins on the apical side and binds mud which can capture astral microtubules and orientate the spindle.
51
what do mutations in mud result in?
faulty spindle orientation
52
what happens when you perturb neuroblast asymmetric division vi mutating asymmetric components?
get over proliferation and tumour formation
53
where do neural progenitors arise from in vertebrates?
from thhe subzventriuclar zone or the ventricular zone
54
what is the different between VZ progenitors and SVZ progenitors?
- VZ progneitors replicate their DNA with their nuclei in the basal half of the ventricular zone. the nuclei then translocates to the apical side to undergo mitosis
- the nuclei of theSVZ do not undergo movement and remain in the SVZ during the cell cycle.
55
are the VZ cells polarised?
yes have clear apical and basal sides
56
what is the general consensus for the role of spindle orientation in the VZ of verts?
VZ progenitor cells mostly have a fixed spindle orientation along the planar axis and that correct spindle orientation is not for determining daughter cell fates but for proper organization of the neuroepithelium.
57
what is thought to be the role of numb in vert neural progenitor development?
- it is a key determinant of asymmetric daughter fate in flies and there is a homolgue in mouse.
- it is thought that slight changes in numb inheriance of daughter cells could result in different fates
- hence how slight changes in the spindle orientation even though mostly in the same orientation, could affect cell fate
58
what is the alignment of the majority of spindle in the vertebrate VZ cells?
planar, parallel to the ventricular surface
59
generally how is the neuroectoderm divided by genes acting along the Ap and DV axis?
into a checkerboard pattern or neural equivalence groups
60
what happens to the cells that dont become neuroblasts in the neural clusters of the fly?
they become epidermis
61
where do the neuroblasts migrate to after they bud off in the fly?
they go inside the fly
62
how is the AP identity of the pro neural clusters?
the segment polarity genes control gene expression along the AP axis and enable NBs that form in different AP rows to acquire different fates
63
what patterns the DV axis so the fly ventral nerve cord?
NK-Kb/EG signalling gradient patterned by BMP from the dorsal
64
what are the three stripes of DV lines in the ventral nerve cord
vnd, ind, smh
65
what are neural equivalence groups?
groups of cells in the ventral neural chord in the fly that are patterned in a certain square of the checkboard
66
is it thought that the process by which one cell from the pre neural cluster is random?
no- thought there is some kind of initial bias maybe
67
what is the result of the different neural equivalence group expresison patterns?
they give a slightly different identity to each neuroblast. As all known NB identity genes encode transcription factors, it seems that NB identity is deter- mined largely at the transcriptional level; however, the molecular logic through which distinct sets of transcrip- tion factors trigger specific NB identities remains unknown.
68
how is the fate of the GMS determined?
it is generally thought that it is controlled by time> there is a sequence of 5 Tfs that a re express, HB, Kr, Pdm, Cas and gh. During the first round of division of the NBs, Hb will be expressed and determine the fate, during the second round, Kr will be expressed in the GM. etc etc
69
what are the 5 TFs expressed in the NB over time?
hunchback, kruppel, pdm, Castor and grainy head
70
how do the 5 Tfs of the NB control each other?
Hunchback will stimulates Kruppel (which stimulates pd.) but will inhibit pdm so that only kruppel will be expressed. the same for kruppel and cas
71
how is the asymmetry of the GMCs determined?
the Notch signaling pathway acts in opposition to that of numb to enable most, if not all, GMCs to divide asymmetrically to produce sibling neurons with distinct fates. As in NBs, a protein complex containing Inscuteable coordinates the asymmetric localization of Numb with the mitotic spin- dle, such that Numb segregates exclusively into one daughter cell on GMC division (apparently)
72
what three cell types are produced by the fly Nbs?
motor neurons, interneurons and glia
73
are the NBs biased towards a certain neuronal type?
no can form any
74
why would it be important to segregate some components into one side of the cell during asymmetric division?
to help the progenitor maintain its steamness
75
how can the environment influence the outcome of progenitor cell division? (2)
- they can act in an 'instructive' manner, biasing the outcome of the division process and causing the stem cell to adopt one fate at the expense of others. Or they can act in a selective manner permitting the survival and maturation of only certain cell progeny
76
which cells act the the structural scaffolds to neural progenitors? how do they do this?
radial glial cells- their cell bodies are found in the ventricular zone and their long process extends to the pill surface. As the brain thickens, the processes of radial glacial cells remain attached to the ventricular and pal surfaces. After generation of neurons, many radial glial cells differentiate into astrocytes
77
what was the classical view of the sets of cells in the ventricular zone and how hhas this changed?
- it was once thought to contain radial glial cells and a set of neuroepithelial progenitors which served as the primary source of neurons. This classical view has changed. this follows experiments that labelled radial glial cells with fluorescent dyes or viruses and thus tracing of their progeny was made possible and revealed cell clusters that contain both neural and radial glial cells. This indicate that radial glial cells are able to undergo both asymmetric and self renewing capabilities.
78
how cod radial glial cells make the decision to self renew, generate neurons, or give rise to mature astrocytes?
- in flies and vertebrates the neural fate is regulated by a cell surface signalling system comprised of delta and notch. In flies the pro neural region is defined by expression of pro neural genes which encode TFs of bHLH class. yet within this region, only certain cells will form neurons and the others will become epidermal support cells. “The binding of Delta to Notch results in proteolytic cleavage of the Notch cytoplasmic domain, which then enters the nucleus. There it functions as a transcription factor, regulating the activity of bHLH transcription factors that suppress the ability of the cell to become a neuron and reduce the level of expression of the ligand Delta. Through this feedback pathway a minor difference in the initial level of Notch signaling is rapidly amplified to generate an all-or-none difference in the status of Notch activation, and consequently the fates of the two cells. ”
79
how does notch signalling regulate neuronal and glial production in mammals?
at ealry stages in development of the mammalian cortex, notch signalling promotes the generation of radial glial cells by activating members of the Hes family of bHLH transcriptional repressors. Two of these proteins, Hes1 and Hes5 appear t maintain radial glial cell character by activating the expression of an ErbB class tyrosine kinase receptor for neurkgulin, a secreted signal that promotes radial glial cell identity. The notch ligand delta is expressed in the newly formed cortical neurons, thus radial glial cells depend on feedback signals from their neuronal progeny for continued production
80
does the expression of notch or delta promote neural fate?
delta
81
how does the role of notch signalling change during development?
- notch signalling continues to activate Hes but it starts to activate astrocyte differentiation instead
82
how do neural precursors inhibit the expression of notch?
they express numb
83
what does the inhibition of notch signalling result in?
expression of several prenatal BHLH TFs such as ngn1 and ngn2
84
what is the role of REST/NRSF?
REST/NRSF, is expressed in neural progenitors and glial cells, where it represses the expression of neuronal genes. REST/NRSF rapidly degrades as neurons differentiate, permitting the expression of neurogenic bHLH factors and other neuronal genes
85
how does the production of the cerebral cortex generally proceed?
in an inside out fashion- first those cells that will populate the regions of the brain that are the deepest layers of the corte. Cells that leave later will settle in the superficial layers of the cortex
86
what is lishencephaly?
0 neurons leave the VZ but fail to complete their migration into the cortical plate. - the mature '6' layer cortex is reduced to 4 normally and the layering is disorders- this disorder arises from mutations related to microtubules- so to do with neuronal migration
87
what is reelin and what happens when it is mutated?
- ECM protein secreted from neurons in the replete zone and marginal zone. When it is mutated neurons fail to fetch from the radial glial scaffold and pile up underneath the cortical plate- disobeying the inside out rule - the layering is reversed
88
how can radial glial cells provide scaffolding to migrating radial neurons?
their cell bodies are located close to the ventricular surface and give rise to elongated fibres that span the width of the developing cerebral wall. at radial glial cell has one basal end foot in the VZ at the apical surface and processes that terminate in multiple end feet at the pill surface of the brain.
89
how many migrating neurons can radial glial cells support?
around 30
90
describe how elongation progresses in the neurons climbing up the radial glial cells
“The microtubular cytoskeleton has an important role in neuronal migration. Microtubules envelop the nucleus in a cage-like structure. Migration involves elongation of the leading process of the neuron in the direction of movement, under the control of attractive and repellant extracellular guidance cues. These cues regulate the phosphorylation status of the microtubule-associated proteins Ndel1 and Lis1 (two components of the dynein motor complex) and of doublecortin (Dcx), which together stabilize the microtubule cytoskeleton. The centrosome then moves into the elongated process, the nucleus is pulled in the direction of the centrosome by the dynein complex, and the two become attached. Disruption of Dcx, Ndel1, or Lis1 impairs interaction between the nucleus and centrosome and disrupts neuronal migration.”
91
what is tangential migration?
- used to populate distinct regions of the nervous system and may have evolved as a mechanism for increasing the complexity of neuronal circuits. Its major cellular substrate appears to be preexisting axonal tracts that connect regions of neuronal generation with the spinal settling position of the neurons
92
in the fly, how are the different layers/ of neurons in the neural tube patterned
as the cells proliferate the GMCs produce two neurons, then as time goes on the expression of the neuroblast changes so that the next GMC will express another TF and will ave another fate- this will push the first 2 up and then will for the second layer and so on
93
what mediates the localisation of basal components to that side
the par proteins
94
what is the role of the G protein cassette in the neuroblast of the fly
it contains Galphai, Pins and loco and also insucteable- will bind and orientate the spindle
95
how does numb interact with notch?
it will bind to the intracellular domain of notch and inhibit it
96
what facilitates the asymmetric localisation of numb?
pon
97
what are the two types of division that a radial glial cell can undergo? how was this investigated?
In an elegant set of studies, Noctor and colleagues labelled single RGCs with a green fluorescent protein (GFP) in the developing rat neo- cortex, observed them through several rounds of div- isions, and followed with histochemical and electrophysiological assays to determine the fates of the daughter cells. Their findings show that RGCs undergo two types of asymmetric divisions . One type is neurogenic, during which an RGC divides to produce another RGC (self-renew) and a daughter cell that becomes a neuron. Another type, which in a way resembles the division pattern of Droso- phila neuroblasts, generates two daughter cells that both re-enter cell cycle, but one remains in the VZ whereas the other moves to the SVZ and divides only once to generate two neurons.
98
because of the vertical division in the vertebrate system, what is the general idea about how asymmetry can form?
the apical surface of the cells actually only represents 2-4% of the cell membrane so it may be that this is not significant- instead, slight biases in th inheritance of cytoplasmic compoentsn may be important
99
in the mouse, inheritance of which compoentsn confers neuron vs neuoblast fate it is thought?
the Radial glial cell: the basal projection, numb, Par complex, increased notch and apical membrane
the neuron: decreased notch, delta like 1
100
in the zebrafish, inheritance of which compoentsn confers neuron vs neuoblast fate it is thought?
radial glial cell: no apical - basal projection membrane increased notch
neuron: par proteins
101
what is the division angle thought to be in vert?
oblique
