ectoderm and nervous system Flashcards
from what germ layer is the nervous system derived from
the ectoderm
from what are all the nerves and glia cells derived from
the neural plate/tube: forms all CNS nerves
the neural crest: forms all the PNS nerves in the body and some in the head
placodes: forms some of the PNS cells in the head
how is the ventral- dorsal axis formed in neural development
BMP-FGF signalling
the organiser node secretes the BMP inhibitor FGF, creating a gradient
areas with lots of BMP will become the ventral side
areas with lots of BMP inhibitors (like FGF) will become the dorsal side
how does BMP-FGF signalling decide which tissue forms the nervous system
areas with lots of BMP signals will become epidermal tissues
areas with BMP inhibitors (FGF) will become neural tissue
(this means the neural tissue will always be on the dorsal side)
what happens during neural induction
BMP-FGF signalling work together to induce neural fate
the result is that the neural plate is formed along the midline of the blastula
what happens during primary neuralation
the neural plate folds up to first form the neural folds and then the neural tube.
the midline of the plate will become the bottom of the tube
the lateral edges will fuse to become the top of the neural tube
what is secondary neuralation
the end section of the neural tube is formed by secondary neuraltion
tail bud cells condense around a central lumen through epithelialisation
essentially, a cluster of cells is hollowed out
where is the neural crest formed
at the border between the neural ectoderm and the epidermal ectoderm
what are the two paths that neural crest cells migrate down
Dorsolateral path and the ventromedial path
neural crest cells that follow the ventromedial path can only move across the ventral side of somites, this forms segments across the embryo
what are the different cell fates for neural crest cells
the fate is dependant on their position of origin
if they are in the head they will form most the glia cells in the CNS
If they are in the trunk they will form root ganglia, enteric ganglia the automatic nervous system and Schwann cells
what are the different diseases that arise when neural crest development goes wrong
Hirchspurg disease
DiGeorge syndrome
how many domains of progenitor cell are there
there are 5 domains of progenitor cell
they are expressed by SHH signals acting on homeobox genes
the floor plate and notochord secrete SHH which creates a gradient, triggering different homeobox genes
how many vesicles make up the CNS
initially 3 vesicles form (forebrain, midbrain and hind brain). later 2 more vesicles will develop (5 total)
what is Otx2
Otx2 is a hot gene that defines that anterior portion of the brain, (midbrain and hindbrain).
when Otx2 is knocked out the organism will not develop a head.
what is the isthmus
the region of the brain where the midbrain and hindbrain meet.
it patterns the midbrain by FGF8 signalling
if the isthmus is grafted onto another embryo, it will develop two midbrains in a mirror image duplication
what is FGF8
a signalling molecule that is secreted at the Isthmus and anterior neural ridge.
it induces the formation of the telencephalon, mesencephalon and rhombocephalon
how is the identity of each rhombomere decided
the 4 Hox genes (Hoxa2, Hoxab1, Hoxa3 and Hoxad4) determine the identity of each rhombomere through joint expression. by changing the expression patterns of each gene, we can change the identity of the rhombomere
what are neuromesodermal progenitor cells
unique mesodermal cells that are able to form neural tissue in the brain (the nervous system is almost entirely ectoderm derived).
They express a dual fate and are able to become either neural or mesodermal cells
how is the early neural tube organised
the neural tube forms pseudostratified columnar epithelium with a marginal end and a ventricular end
the nuclei of cells within the tube will migrate from the marginal end of the cell where DNA synthesis takes place to the ventricular end where cell devision takes place.
what are the three layers of cells that arise during the histogenesis of the neural tube
ventricular layer: epithelial cells (radial glia) that keep dividing and differentiating
Mantle layer: newly formed neurones
Marginal layer: The axons from the newly formed neurones all move towards the marginal side, forming the marginal layer
How do cells within the neural tube differentiate
they start off as neural progenitor cells (Sox2 expression)
next, neurogenic regions are defined through the expression of NeuroG and Ascl
Finally the selected cells within the neurogenic region express NeuroD and can become nerve cells
how is cell differentiation within the neural tube regulated
FGF signalling
FGF is secreted at the Isthmus and the anterior neural ridge
FGF prevents the formation of neurogenic regions
This means that Neurogenic regions can not form uncontrollably.
inhibition of FGF signalling causes the neurogenic region to invade deep into the mescencephalon.
how are cells selected to be neurones within the neurogenic region of the brain
lateral inhibition through Delta-Notch signalling
-All neurogenic cells produce Ascl and NeuroG
-these activated Delta ligands which trigger notch receptors on its neighbours
-Notch receptors activate the transcription factor Hes
-Hes inhibits Ascl and NeuroG
When a cell produces enough Delta through random chance it will prevent its neighbours from developing into neurones
what are neuroepithelial cells
neuroepithelial cells are stem cells that are able to differentiate via asymmetric cell devision to produce one stem cell and one differentiated cell
They differentiate into Neurones, glia (usually after neurones) and other cells associated with the brain
