Intro to developmental neuroscience Flashcards
Induction
signal originating in one tissue that causes another responsive tissue to differentiate into something else
Inducer
chemical signalling molecule
short range or long range
from stem cell to neuron
competent neural precursor
specified neural precursor
committed neural precursor
differentiation
from stem cell to radial glial cell
neuroepithelial cells
early radial glial cell
neuron or late radial glial cell eg astrocyte
can replenish previous pool
Model organism example and steps in development
xenopus
egg - blastula - gastrula - neurula
2 poles of egg
vegetal - unpigmented, heavy, full of yolk
animal - pigmented
Where does grey crescent form?
directly opposite where sperm enters
what does grey crescent determine?
d/v axis - ventral = sperm comes in, dorsal = grey crescent
what does 1st division do to grey crescent?
splits it in half
animal pole cells are?
smaller
gastrulation
cells migrate towards inside of embryo through the blastopore to form 3 germ layers
ectoderm
CNS, PNS, skin, hair
mesoderm
blood, muscle, cartilage, kidneys
endoderm
GIT and RT lining, liver, thyroid
purse string contraction
in neurulation the flat ectoderm thickens to form a neural plate by contraction and then a hollow neural tube
border cells of neural plate become what?
neural crest
neural crest cell migration
laterally to form PNS, including spinal ganglia
What happens to the notochord?
degenerates and only persists in IV discs
contact between notochord and neural tube
physical - allows induction
dorsal lip transplantation
Spemannn and Mangold 1924
Explain dorsal lip transplantation
dorsal lip of blastopore cut out
transferred to ventral site
dorsal lip transplantation control
ventral tissue grafted to ventral position
findings from dorsal lip transplantation
active = 2 neural tubes, 2 complete nervous systems without ventral tissues control = normal embryo
what is the spemann organiser?
dorsal lip of blastopore - able to organise 2nd nervous system
organiser potency with time
early donor - complete 2nd axis
late donor - extra tail only
vertical and planar movement
vertical - between layers of different tissue, late gastrula
planar - within a single plane (early-late gastrula)
early evidence favoured vertical or planar?
vertical
who did the exogastrula experiments?
holtfretter in 1933
explain exogastrula experiment
high salt concentration
planar induction not sufficient for nervous system
must have opposed layers
Mangold 1933
embryo in neurulation - dissect mesoderm and graft into blastocoele
anterior mesoderm - 2nd head
posterior mesoderm - 2nd tail
vertical induction findings mangold 1933
Vertical induction of ectoderm by mesoderm
mesoderm contains inducers that specify A/P nervous tissue
homeobox genes
1983 - genes encoding transcription factors that determine body segmentation
highly conserved from flies
what are homeobox genes markers for?
A/P position
2 homeobox experiments
exogastrula and keller sandwhiches
homeobox - exogastrula
label embryos for neural markers N-CAM and xhox3 present in ectoderm next to envaginated mesoderm
What lead to a rethink that not only vertical induction was involved?
homeobox genes
Keller sandwhiches
2 embryos - cut out identical regions
later them under piece of glass and allow to develop
keller sandwhich findings
homeobox genes found in same position in embryo and keller sandwhich
no vertical induction
Is planar induction enough?
No - no floor plate, no D/V patterning
keller sandwhich - no eyes, anterior structures
What is the default state for ectoderm?
neural tissue
Evidence for default model
xenopus - animal cap
intact tissue = epidermis
reaggregate immediately = epidermis
delay reaggregation for 1 hour = some neural markers
reaggregation delayed >5 hours = neural tissue only
neural default model - explain
absence of signal required for neural differentiation
no signal = neural
Neural default model reinterprets spemann and mangold
epidermal inducer in ectoderm an receptor - bind epidermal induction
spemann organiser produce antagonist - neuronal
