BIOL 303 Lecture Notes - Lecture 12: Surface Ectoderm, Neural Tube, Neural Fold
14 May 2018
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Department
Course
Professor
Biol 303 March 15th
General
• Discussing the development of the nervous system
• Neural tube formation
• Specification of cell identity in the nervous system
• Formation and migration of neurons in the central nervous system
Development of the nervous system
• Gastrulation = formation of the three layers in the embryo
• The ectoderm gives rise to the nervous system
• Not EVERY part of the ectoderm gives rise the to nervous system → only the central
dorsal portion of the ectoderm does
• The central part of the ectoderm is the neural plate which becomes the neural fold
• The neural tube gives rise to the entire central nervous system
Why does only the dorsal ectoderm give rise to the nervous system
• Experiment: isolate ectoderm cells from the gastrula and culture them in vitro, without
communication between cells → they become neural tissue
• Therefore, the default fate of ectoderm cells is neural fate
• This occurs in the absence of inhibitory signals
• Another question now: what is the inhibitory signal in the ventral region that prevents
those ectodermal cells from becoming neural cells?
TGB-Beta
• Turns out, the inhibitory signals are TGF-Beta family proteins → these are secreted,
diffusile proteis that id to reeptors o ell surfaes to deterie the ell’s fate
• BMP4 – a TGF-Beta protein
• If you incubate the isolated ectoderm cells with TGF-Beta, they become epithelial cells
• Therefore, the TGF-Beta proteins act as inhibitory signals
Noggin and Chordin
• Produced by the organizer
• If you look at the dorsal ectoderm, beneath it there is the dorsal mesoderm → the
dorsal mesoderm cells produce Noggin and Chordin
• What do Noggin and Chordin do??
• Noggin can bind to BMP4 and prevent it from binding to its receptor (thus no inhibitory
signal)
• So, if you add both BMP4 and Noggin to isolated ectodermal cells, they become neural
cells because Noggin blocks the inhibitory action of BMP4
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find more resources at oneclass.com
Mechanical forces driving neurulation
Formation of the neural tube
• If you look at the central portion of the ectoderm, cells located in that region become
elongated along the dorsal-ventral axis – it looks different morphologically
• The elongation is dependent on microtubules
• If you use colchicine on it (the embryo), it can disrupt microtubule mobilization and
prevent the formation of the neural plate
• Neural furrow: cells located in the descending region undergo changes that lead to the
formation of the furrow structure → these processes are sensitive to cytochalasin B
(which disrupts the actin cytoskeleton)
• The next step is the formation of the neural fold: due to external force from surrounding
ectoderm → these forces push the fold region up
• Next: the two neural folds become close to each other and eventually fuse with each
other → leads to the formation of the neural tube → the surface ectoderm forms above
• The neural tube tissue separates from the surface ectoderm → this segregation is made
possible by differential cell-cell adhesion
• The neural tube expresses N-cadherin which is a hemophilic cell adhesion molecule →
can associated with other cells expressing N-cadherin
• The surface ectoderm expresses E-cadherin → cannot bind with N-cadherin
Neural Tube
• Has an anterior and posterior side
• The newly formed tube will differentiate along the anterior-posterior axis and dorsal-
ventral axis → giving rise to different neural cell types and different structures
• Anterior region → brain
• Posterior region → spinal cord
Anterior end – brain
• In the beginning, it expands to form brain structures
• Starts with three structures: most anterior = forebrain, then midbrain, then the
hindbrain is most posterior
• Forebrain = smell, memory, intelligence, vision, etc.
Why does the anterior region become the brain?
• Found the protein otx2 → a brain specific transcription factor
• If you knock out otx2 → loss of forebrain and midbrain structures
• In Drosophila, there is orthodenticle (otd) and if you knock it out, it leads to the loss of
the head structures
• Otd is a homolog to otx2
Expression pattern of otx2
• Located in the regions of the forebrain and midbrain
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
General: discussing the development of the nervous system, neural tube formation, specification of cell identity in the nervous system, formation and migration of neurons in the central nervous system. If you incubate the isolated ectoderm cells with tgf-beta, they become epithelial cells. Noggin and chordin: produced by the organizer. If you look at the central portion of the ectoderm, cells located in that region become elongated along the dorsal-ventral axis it looks different morphologically: the elongation is dependent on microtubules. In the beginning, it expands to form brain structures: starts with three structures: most anterior = forebrain, then midbrain, then the hindbrain is most posterior, forebrain = smell, memory, intelligence, vision, etc. Why does the anterior region become the brain: found the protein otx2 a brain specific transcription factor. If you knock out otx2 loss of forebrain and midbrain structures.
