Neurulation Flashcards
What induces neuroectoderm formation?
primary organizer
What are 3 ectodermal derivatives important for neurulation?
What are their levels of BMP expression?
surface ectoderm (high BMP) neural crest (moderate) neural crest/tube (low)
What is derived from surface ectoderm?
epidermis hair, nails sebaceous glands olfactory epithelium mouth epithelium lens, cornea
What is derived from neural crest?
PNS adrenal medulla melanocytes facial cartilage dentine of teeth
What is derived from neural plate/tube?
brain neural pituitary sinal cord motor neurons retina
Name brain vesicles at 3-vesicle and 5-vesicle stage.
prosencephalon –> telencephalon, diencephalon
mesencephalon –> mesencephalon
rhombencephalon –> metencephalon, myelencephalon
What defines the neural plate territory?
BMP4 induces neural to epidermal transition
it is inhibited by Chordin, Noggin and Folistatin from the primary organizer
type of cell differentation is determined by Fgf signaling via Smad1 (TF)
Describe neurulation (and secondary neurulation in the posterior part).
neural and epidremal ectoderm in the embryo at the neurula stage have differentialy expressed adhesion molecules:
E-cadherin in presumptive epidermis
N-cadherin in neural plate
1) formation and folding of the neural plate
2) shaping and elevation of neural plate
cells in the dorsal ectoderm elongate
undergo apical constriction at the medial hinge point –> 2 dorsolateral hinge points
3) convergence of neural folds
4) closure of the neural groove
neural groove forms
because of cell adhesion and repulsion between different adhesion molecules, neural tube closes and is now detached from epidermis above it
in between the two: neural crest cells -> migration
secondary neurulation happens posteriorly as the axis elongates
cells dont undergo actual invagination, but cluster together beneath the epidermis (MET)
What do we mean by saying calling neuroepithelium pseudostratified?
it looks like it is multilayered, but it’s actually not
all cells extend across it’s whole width
but the illusion of multiple layers comes from interkinetic nuclear migration: nucleus of the cells travels up and down based on the stage of cell cycle it is in
(nucleus is closest to the lumen of the neural tube during metaphase; then it undergoes asymmetric cell division to form neu neural progenitors and the nuclei move back up)
Where is ventricular zone of the neuroepithelium in relation to neural tube lumen? Apical of basal side?
ventricular zone = apical side
Which cells develop from neuroepithelial cells?
neuroepithelial cell -> radial glia cell -> neuron or oligodendrocyte/astrocyte/ependymal cell
How are stem cells of the neocortex dividing to produce
a) more stem cells
b) commited cell types?
a) symmetrically
b) asymmetrically
Which pathway is used for maintaining progenitor cells?
Notch-signaling
for lateral inhibition
(salt and pepper pattern)
neuron expresses Dll to inhibit neuronal fate of neighboring cell
Describe segmentation of hindbrain into rhombomeres.
rhombomeres (1-7) are transient compartments
- cells in each are lineage restricted
- Eph/ephrin expression to prevent mixing
identity of each rhombomere is defined by expression of different Hox genes (more in posterior neural tube)
Which are the 3 signaling centers within neural tube?
anterior neural border
isthmic organizer at MHB
zona limitans intrathalamica
Describe anterior neural ridge.
secondary organizer forms at the rostral end of neural plate induces anterior forebrain formation expresses FGF Wnt and BMP are inhibited - Wnt antaonists are secreted by the ANR AND prechordal plate (A part of notochord)
What is isthmic organizer?
expresses FGF8
allows clear separation of mid- and hindbrain
What is the role of zona limitans intrathalamica?
organizes the development of prethalamus and thalamus
Which morphogens are expressed on dorsal and which on ventral side of neural tube?
dorsal: BMP, Wnt
ventral: Shh
How are borders along DV axis of neural tube refined?
mutual repression of TFs: class I: inhibited by Shh class II: activated by Shh
Which tissues induce DV patterning (roof and floor plate)?
roof plate: ectoderm induces expression of TGF-B
floor plate: notochord and prechordal plate induce expression of Shh
Which gradient is induced by Shh expresion in the floor plate and how?
Pax6
Olig2
Nkx2.2
Shh activates Gli
Gli represses Pax6
as Shh gradient becomes stronger and moves dorsally:
Nkx2.2 area forms below Olig2
(mutual inhibition of these two)
