8. Development of the Nervous System Flashcards
what is the first stage of embroygenesis
cleavage
describe the first two cleavages
perpendicular equal and holoblastic
why is cleavage 3 different from cleavage 1 and 2
it is no unequal and holoblastic
cleavage continues until how many cells are made
32
during cleavage what is the early embryo contained in
the zona pellucida
once it reaches 32 cells what is the embryo now termed
a morula
what occurs during the compaction stage
cells get closer together and the cells on the outside differentiate into trophoblast cells.
the inner cells are called embryoblasts
what occurs on day 5
embryoblast cells clump together at one end, the remainder of the space inside the layer of trophoblast cells becomes the blastocoel
what is a blastocoel
a fluid filled cavity
what happens to the zona pellucida on day 5
what does this facilitate
it decomposes and is replaced by the underlying layer of trophoblastic cells
this facilitates implantation into the endometrium
what then occurs to the inner cell mass
it flattens out, the two cells become epiblasts and the layer below become hypoblasts
what is the term given for the inner cell mass once it has flattened out
the bilaminar disk
once the bilaminar disk is formed, what happens next
the primitive streak forms at the midline of epiblast cells, from this they ingress into the blastocoel
what dictates epiblast fate
the order of which they enter the blastocoel
the first cells become endoderm
the middle cells become mesoderm
the last cells become ectoderm
name 2 things the endoderm goes on to form
liver
lungs
name 2 things the mesoderm goes on to form
muscle
blood
name 2 things the ectoderm goes on to form
all parts of the nervous system
ear
lens of eye…
what directs the migration of epiblast cells into the blastocoel
the organiser
what determines the dorso-ventral axis
the point of sperm entry = ventral side
from this microtubules contract and the cytoplasm rotates facilitating the formation of a signalling centre on the dorsal side
what is the name of signalling centre generated in response to sperm entry
the nieuwkoop centre
describe the process of mesoderm specification along the axis
- BMP4 is expressed in the marginal zone and induces ventral mesoderm
- VegT and Vg1 induce nodal-related in the vegetal hemisphere
- beta catenin boosts nodal related in the nieuwkoop centre which induces dorsal mesoderm and the organiser
- the organiser produces chordin which acts as a dorsalising signal
- colloid cleaves chordin in the vegetal hemisphere allowing BMP4 to act.
what does the dorsal most aspect of mesoderm develop into
the notochord
what does the ventral most aspect of mesoderm develop into
blood
name the organiser in chicks
hensens node
name the organiser in amphibians
spemann’s organiser
name the organiser in mammals
primitive knot (or node)
describe Spemann and Mangold’s experiment
they confirmed the role of the organiser by transplanting tissue from a pigmented embryo into a non-pigmented embryo
this could induce the formation of two new embryos by implanting the specific tissue that included the organiser
what happens if you cut a blastula in two
the ventral side will not develop into muscle - only ventral mesoderm fates such as blood develop
the organiser must be present in the dorsal marginal zone to produce muscle
what happens if you induce beta-catenin mRNA into the ventral side of the vegetal region
a second nieuwkoop centre will develop and duplicated axis will develop
what signalling molecule is essential for specifying the nieuwkoop centre
Wnt
what does the notochord form from after gastrulation
mesoderm cells
what do signals from the notochord do?
drive inward folding of ectoderm at the neural plate
what happens after the neural plate is formed
the ends fuse and disconnect to form an autonomous neural tube
once the neural tube is formed, which bit does the brain and spinal cord develop from
the brain forms from the anterior end
the rest of the tube forms the spinal cord
what tissue is the neural tube derived from
ectoderm
what molecule inhibits neurulation
BMP4
what happens to ectodermal cultures with BMP4
they differentiate into epidermis rather than neural cells
name 3 molecules that inhibit BMP4
chordin
noggin
follistatin
what is the evidence that BMP4 is an inhibitor of neurulation
KO mice for chordin and noggin = BMPs are not inhibited so epidermal fate is not inhibited and neural fate is not induced
produces mice without a forebrain, nose or facial structure
do it again! describe the process of neurulation! hahah
- neuroectodermal cells dive down and differentiate into the neural plate
- on either side of the neural plate is a band of cells called the neural crest
- neural plate invaginate and the neural crest tissue sitting at the top forms the neural groove
- the neural groove pinches off forming an autonomous neural tube
what do neural crest cells eventually produce
peripheral nervous system neurons
what happens to the notochord after neurulation
it is only retained in some primitive chordates (e.g. hagfish)
in most higher order vertebrates it is replaced by the vertebral column
what does fusion of the neural plate require
cell adhesion molecules: N-cadherin and N-CAM
what process stops the binding of neural tissue to epidermis, and why
homophillic adhesion
they can now recognise each other as being the same
neural crest cells show some plasticity, depending on their positional cues what do they produce?
either sympathetic or parasympathetic neurons depending on their anterior-posterior position.
