Of development (Neurulation)
65 important questions on Of development (Neurulation)
What are the three things that happen during the third week?
- The three layers are formed
- The body axis are determined
- Gastrulation leads to formation of primary organs/tissues
What are two important things that happen during the process of gastrulation after the bilaminar disk has become a trilaminar disk?
- The neural groove in the ectoblast forms
- The notochord forms
To what kind of tissue does the ectoderm give rise?
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To what kind of tissue does the mesoderm give rise during the third week of development?
To what kind of tissue does the endoderm give rise during the third week of development?
What are the three new body axis formed during the third week of development?
- Cranial-caudal
- Medial-lateral
- Left-right
What is the body axis that already existed before the third week?
What three things does the primitive streak consist of?
- Primitive pit
- Primitive node
- Primitive groove
What do epiblast cells do at the primitive streak?
How do FGF-8 cells (primitive streak) become more loosely attached?
What kind of cell type transformation takes place?
What happens after definitive endoderm is formed, and the EMT has happened?
In conclusion, from what cell type are ecto-, endo-, and mesoderm derived?
What are the 4 structures where extraembryonic mesoderm can be found?
- Chorion (inner layer)
- Allantois (outer)
- Amnion (outer)
- Yolk sac (outer)
What cell type can be found at the tip of the primitive streak?
- Gut endoderm
- Prechordial plate
What is meant by the anterior migration of intraembryonic mesoderm?
What are the layers at the prechordial plate (at the cranial side)?
What are the prechordial plate and the notochord important for?
In what direction does epiblast-to-ectoderm transformation take place?
From cranial to caudal sequence, what are the mesoderm types that are derived from the primitive streak?
2. Head mesoderm (HM & neural crest contribute to head mesenchym)
3. Paraxial mesoderm (somites; vertebrae, muscles)
4. Intermediate mesoderm (kidneys, urogenital tract, etc.)
5. Lateral plate mesoderm (limbs, lining body wall)
What is the function of the primitive streak?
What is the function of the axial mesoderm (notochord)?
What are the four types of mesoderm in this stage of embryonic development?
2. Chorda-mesoderm (forms into notochord)
3. Paraxial mesoderm
4. Lateral plate mesoderm
What are the three types of mesoderm formed from the lateral plate mesoderm?
- Splanchnic (visceral) mesoderm
- Somatic mesoderm
- Extraembryonic mesoderm
What determines the type of mesoderm certain cells become?
What happens to the paraxial mesoderm cells?
What does the segmentation clock determine?
What happens with somite number 1-4, and what happens with somites 5-37?
- Somite number 5-37 become somites.
In what way does paraxial mesoderm formation happen?
What causes the start and stop signals for somite formation?
What causes the start of the development of a somite?
AND
- High cycling genes
What is important in the study of the level of gene expression in somite formation?
In what direction are somites formed?
The gradient of factors is important. How is the movement of factors along the cranio-caudal axis of the embryo?
- Expression of cycling genes comes and goes from caudal to cranial direction
(so coinciding low levels of RA/FGF8 and high levels of cycling genes determine somite formation)
What determines the boundary & size of a somite?
- Wnt + FGF,
- and RA
What are the three things somites eventually differentiate into?
- Dermatome (skin)
- Myotome (muscle)
- Sclerotome (spinal vertabrae, skull basis)
Where does the lateral mesoderm form in the embryo?
Where does the paraxial mesoderm mainly form?
What do somatic/parietal mesoderm and splanchnic/visceral mesoderm end up in?
- The splanchnic/visceral mesoderm together with endoderm becomes the gut wall
(take a close look at the picture)
What does the lateral plate mesoderm do when the embryo starts to fold?
What has happened in children with anencephaly, and what has happened in children with spina bifida?
- Spina bifida: closure of neural tube is not completed at the caudal side
What two types of ectoderm are formed during the process of ectoderm formation?
- Neural plate ectoderm (= brain)
- Peripheral surface ectoderm (= finally skin epidermis)
In what direction does ectoderm form?
What happens after the germ layers are complete?
What does the zone of ectoderm (neural plate) do on the dorsal site of the embryo?
What kind of effect does the notochord have on this process?
On which day of embryonic development is the neural plate formed?
What do the neural tube and the neural crest become?
- Neural crest: peripheral nervous system (PNS)
Where do the neural crest cells appear?
What kind of cells are formed from a neural crest progenitor?
- Sensory neurons, adrenal neurons, cholinergic neurons
- Melanocytes
etc
What are 4 main players and 2 other players in the formation of the neural plate (ectoderm formation)?
- Sonic hedgehog (Shh)
- Fibroblast growth factor (FGF)
- Wnt
- BMP4
Other players:
Chordin and Noggin
What is the function of BMP4 in neural plate formation?
- Its absence determines the position of the neural plate
What happens at the place of the neural plate around day 18?
- BMP4 is inhibited by FGF
- absence of BMP4 determines the neural plate
How does FGF inhibit BMP4, and what other factor inhibits BMP4?
- Chordin & Noggin inhibit BMP4 activity
Where is FGF present, and where is Shh located?
- Shh is present in the notochord (forebrain)
What are three things BMP4 does?
- Transforms epiblast into epidermis (skin)
- Transforms mesoderm into lateral & intermediate mesoderm
- Activity of BMP4 in the dorsal part of the neural tube is important for the DV-axis
What is Wn3a and FGF expression from the somites important for?
What is retionic acid (RA) important for in this stage?
BMPs and Shh initiate a signaling cascade. What does this cascade define?
How does this BMP and Shh cascade define the motory system from the sensory system?
- BMP is expressed in the sensory areas at the alar plate (dorsal site)
The downstream factors of BMP (PAX3&7) form a gradient with the downstream factors of Shh (NKX2&6, PAX6)
What happens in the neural crest cells at the beginning of neurulation?
How is the BMP level in these cells, and what defines the border in the neural crest?
- Wnt & FGF induce transcription factors PAX3 to specify the border
How is the space within the neural tube called?
In which two direction does the closure of the neural tube occur?
- In medial-to-caudal direction
What would happen if an embryo has higher levels of FGF during the process of neural plate formation?
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