3. Transforming the Neural Plate into
a Neural Tube
• The main protein regulating neurulation is the morphogen
BMP (bone morphogenic protein)
• The Sox family (Sox1, 2, and 3) of transcription factors are
primarily responsible for this phase. They do the following:
• Activate genes that specify cells to be neural plate cells
• Inhibit formation of the epidermis and neural crest cells
by blocking BMP
5. Primary Neurulation
• Primary Neurulation is divided into four stages:
• Elongation and folding of the neural plate- cell divisions
occur in the anterior-posterior direction
• Bending of the neural plate- there are cells at the midline
of the neural plate. They form the medial hinge point
(MHP) The cells here are anchored to the notochord
below it. The hinge will create a neural groove
• Convergence of the neural folds- There are two
dorsolateral hinge points (DLHP). This anchors the the
ectoderm and starts to direct growth towards the midline
(the neural tube is starting to get pinched off)
• Closure of the neural tube- the two DLHPs are brought
together at the midline. The folds adhere to each other.
6. Regulation of Hinge Points
• The cuboidal epithelial cells of the neural plate need to
change their shape to a more pyramid-like shape
• Actinomyosin complexes are at one end of the cell and help
create this shape. This is known as apical constriction.
• There is also a thickening of the basal ends of the cells
7. Regulation of Hinge Points (cont.)
• BMP inhibits both MHP and DLHP formation.
• Shh is secreted from the floor plate and notochord, and
it also inhibits hinge formation
• Noggin inhibits BMP. This will allow the hinges to form.
• For apical constriction there needs to be low BMP and
Shh levels (they are morphogens)
8. Neural Tube Closure
• In amniotes, the closure occurs from the anterior to
the posterior rather than all at once
• Neuropores are openings at each end of the neural
tube
• The neural tube is eventually a closed cylinder. This is
because of adhering molecules
• E-Cadherin is initially in the cells that will be the neural
tube, but it switches over to N-Cadherin.
• Because of this, the ectoderm and the neural tube
stop adhering to each other
9. Neural Tube Defects
Two common ones are Spina Bifida and
Anencephaly.
Spina Bifida is when the posterior neuropore
does not close around the 27th day of
development
10. Patterning the CNS
• Anterior-Posterior Axis- in the anterior
portion, the neural tube balloons into
three vesicles:
• Forebrain (prosencehpalon)- forms
the central hemispheres
• Midbrain (mesencephalon)- will
help with visual and auditory
information
• Hindbrain (rhombencephalon)-
autonomic functions, senses,
equilibrium
