Dev of Ectoderm
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what are the 3 things the ectoderm derives into?
- surface ectoderm
- neural crest cells
- neural tube
what does surface ectoderm go into?
epidermis, hair, nails, sebacious glands, olfactory epithelium, mouth epithelium, lens/cornea
what do neural crest cells develop into?
PNS, adrenal medulla, melanocytes, facial cartilage, dentine of teeth
brain, neural pituitary, spinal cord, motor neurons, retina
where does be neural ectoderm signal come from?
mesoderm directly underneath it
what is the embryo called during neurulation?
big pic primary neurulation?
posterior, tissue becomes mesenchymal then forms a solid cord then forms into a tube
big pic secondary neurulation?
anterior region and the tissues invaginate
what are the cells like in the neural plate?
know what the neural fold and neural groove is
they are columnar
specifics of primary neurulation:
neural plate proliferates, (next to the neural crest cells and then the epidermis is on the outside (slide 11)... invaginates at site of MHP, epidermis/neural crest sides converge at the top - forms neural tube with neural crest cells on top and then the epidermis on top of that
what are the 2 things that cause formation of the neural plate?
- originally 50% of ectoderm is neural plate), the underlying dorsal mesoderm signals above ectoderm to become columnar
- neural plate lengthens and narrows by convergent extension (the x axis shrinks while the y axis lengthens)
How does the neural plate bend
MHP (medial hinge point) is located right above the notocord, these cells undergo apical constriction and become wedge shaped and also you get a decrease in height (due to microfilaments and microtubuels)
what does the surface ectoderm do?
whats purpose of anchoring hinges?
- pushes towards the midline
- anchoring to hinges ensures neural tube "folds inward"
what is the other hinge region that causes neural folds to converge together?
DLHP - dorsal lateral hinge points - anchored to the surface ectoderm - elongates and becomes wedge shaped so they push towards each other
how do neural tube and surface ectoderm separate?
initially all ectoderm expresses e cadherin, but when invagination happens they don't express e cadherin anymore and start to express N- cadherin and N-CAM - why they stick together and lose association to surface ectoderm
and then when the epidermis comes together it expresses e cadherin and sticks together
what happens to neural crest cells?
they stop expressing e cadherin so that they are free to migrate away
what would happen if you injected n-cadherin mRNA into one cell of 2 cell xenopus embryo?
oops check out in book, slide 18
how do the folds come together?
happens first at the anterior end, kind of midbrain, but you get 2 holes at the end that have to close up (A/P neuropore)
when does the neuropore close?
what are the 2 neural tube defects?
anencephaly - happens if anterior part of neural tube(forebrain) doesnt close, those neurons get exposed to amniotic fluid - always results in death
spina bifida - posterior end of nerve tube - depends on degree of damage, the spinal cord is exposed to amniotic fluid and you get a loss of neurons, but not always death (theres a degree of damage)
what is folic acid's role in closing of neural tube?
folate binding protein is the receptor for folic acid and is expressed on dorsal most region of tube prior to fusion (expressed right along those folds right before fusion) so folic acid supplementation lowers risk but you would have to take in first month of pregnancy which is hard to know when you are pregnant
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