Cellular Basis of Neurogenesis Flashcards
neurogenesis
a process by which a neural stem cell/neural progenitors generate neurons
neural tube formation
neuroepithelial cells move from the apical and basal neural tube (where the ECM is)
N-cadherin is the main component of the cadherin junctions
interkinetic nuclear migration
occurs in the cell cycle
nucleus moves up (to basal) and down (apical)
what are the types of progenitors
radial glia
neuroepithelial cells
neuroepithelial cells
adopt a RG shape when the neuronal layer forms at the basal surface of the neuroepithelium. Progenitors remains at the apical surface
neurons occupy the basal surface (mantle zone) - GFP labelled
progenitors occupy the apical surface (ventricular zone) - RFP labelled
division types
symmetrical (8n) - forms 2 daughter cells of similar fates - forms neurons
asymmetrical (3n+1p) progenitor forms progenitor and 1 neuron
indirect neurogenesis asymmetrical (4n+2p) most efficient, progenitor selfs renews, intermediate progenitors expand the neural pool
Timelapse
Noctor et al., 2004
in vivo imaging of single cells labelled by lentivirus/DNA constructs expressing slice cultures of the mammalian brain
apical progenitors divide asymmetrically to form progenitors and neurons
basal radial glia
have no apical attachments, only basal attachments
found in higher mammals (humans/ferrets/apes)
divide asymmetrically for growth and gyrification
role of wnt
induces & orients asymmetrical cell fates
extrinsic factor
Wnt experiment
Habib et al., 2013
wnt proteins are immobolised onto beads
mouse embryonic stem cells grown on a culture dish and are co-cultured with the wnt beads
one distal cell ended up further away from wnt bead, other daughter cell in contact with bead (proximal) inhibited B-catenin
intrinsic factors (drosophila)
1) asymmetrical segregation of cell fate determinants e.g. prospero-GFP
2) perpendicualr alignment of mitotic spindle with molecular cresent
3) sensory organ precursor (SOP) cells divide with cleavages parallel to the molecular cresent that lead to asymmetrical inheritance of cell
form P2a/P2b cell fates
numb
cell fate determinant - needed for progenitor cell maintenance and stops precocious neurogenesis
appears concentrated at the apical end
undergoes oblique cleavage
numb can be asymmetrical inherited
numb mutant
Petersen et al., 2002
too many neurons (thicker mantle layer)
fewer progenitors
where is numb localised
localised to cadherin rich adherens junctions between progenitors
KO of N-cadherin in mice
Zhang et al., 2010
KO conducted via NCad shRNA
increases population of Tbr1+ neurons
decreases progenitor population
benefits of zebrafish
transparent
tiny
fast development
perpendicular vs oblique division
perpendicular division - forms 2 progenitors
oblique division - cells loses apical contact - neuron , cell with apical contact - progenitor
Par3 overexpression
Alexandre et al., 2010
Par3 is an apical polarity protein
co-expression of Par3 in ZO-1 and aPKC
par3 is asymmetrically and symmetrically inherited
neuron inherits par3 domain
notch-delta signalling pathway
delta (sending cell) binds to the notch receptor (in receiving cell)
notch intracellular domain is cleaved and activates transcription of genes
cells which activate N-D pathway become progenitors (difficult to become neuron)
repressing and overexpressing delta in chick retina
Henrique et al., 1997
overexpress dominant negative Delta - overproduces neurons and inhibits progenitor fates
ectopic delta eliminates neurons - if many cells forced to express delta, activate notch on its neighbours and prevents neuron formation
role of mindbomb
tags delta
ubiquitin ligase
exposes cleavage site and allows delta to be cleavaged
localisation depends on Par3 function
weak and strong notch-delta signalling
progenitors which receive delta signals from neighbouring cells - weak
progenitors which receive delta signals from only its descendants (intralineage) - strong signals
transplanting mutant progenitors in zebrafish embryo brain
Dong et al., 2012
cannot deliver delta activation of notch R
mutant cells express dla morpholino (MO) - reduces delta translation
results: no progenitors near the apical surface (lack of RFP), lack of cells undergoing asymmetric division
