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Neurulation

Terms in this set (137)

What is neurulation?
Period of development starting with formation of neural plate and ending with closure of neural tube
What is the neural tube?
Future brain and spinal cord
What forms the three germ layers?
Morphogenetic movements dominating gastrulation
What do morphogenetic movements dominating gastrulation do?
Form three germ layers
Cause cells far apart to come closer
What is the primary inductive event?
Notochord on overlying ectoderm resulting in start of neurulation
What components are required for neurulation?
Inductive signal
Ability of ectoderm to be competent to respond to inductive signal
Regional specification
Inducers of ectodermally and mesodermally derived tissues
Wnt family of proteins
Where is sonic hedgehog protein initially expressed?
Notochord
What does sonic hedgehog protein induce?
Neural patterning
Patterning the somites
What do TGF-beta family of proteins regulate?
Formation of ECM and cell differentiation
What does primary neurulation do?
Divide ectoderm into three sets
What three sets is the ectoderm divided into in primary neurulation?
Epidermis of skin
Neural crest cells
Neural tube
Out of the three sets in primary neurulation, which is internal?
Neural tube
Where do neural crest cells form?
Region that connects neural tube with epidermis
Why does the neural tube have hinges?
Facilitate closure
What is coordinated shape change in the neural tube?
Epithelial cells in plate become tall and columnar
Which epithelial cells in plate don't become tall and columnar in coordinated shape change in neural tube?
Midline
What is the median hinge point in the neural tube?
Cells in middle of neural plate become wedge shaped
Where is the dorsolateral hinge point?
Anterior
Shape of dorsolateral hinge point of neural tube
Cells within neural folds differentiate into wedge shape
What does dorsolateral hinge point do?
Assists in closure of neural tube
Are there lateral hinges in neural tube?
No
What is posterior in neural tube?
Opening
What mediates neural tube closure?
Apical constriction of neural plate cells
Rapid antero-posterior extension
Cell crawling
What cell crawling assists in neural tube closure?
Cell crawling of lateral epidermal ectoderm cells
What does movement of epidermal cells do to neural plate?
Drags neural plate up and inward
Which cell adhesion molecules allow neural groove to be formed from plate?
E-cadherin
N-cadherin
Where does neural plate form?
Anterior
Where does neural plate develop?
Behind primitive node as it migrates caudally during gastrulation
What part of neural plate fails to close initially?
Anterior
Why does anterior region of neural plate fail to close initially?
Large and bulky
Where does neural plate closure begin?
Neck region
Which direction does closure of neural plate proceed?
Posterior
What happens to neuropores?
Anterior and posterior persist
What defects is spina bifida due to?
Closure of neural tube
Malformations of brain and spinal cord
Mildest form of spina bifida
Spina bifida occulta
What causes spina bifida occulta?
Failure of vertebrae to fuse dorsally
Pain or neurological disorder caused by spina bifida occulta?
No
Sign of presence of spina bifida occulta
Dimple or tuft of hair
What is anecephaly?
Absence of major portion of brain, skull and scalp
What causes anecephaly?
End of neural tube fails to close
What happens in rachischisis?
Posterior neuropore of neural tube fails to close
Consequence of rachischisis
Spinal cord does not fully form
Remains unfused and open
Types of spina bifida
Occulta
Meningocele
Meningomyelocele
Domains of neural crest
Cranial
Trunk
Vagal and sacral
Cardiac
What does cranial neural crest consist of?
Cartilage
Bone
Cranial neurons
Glia and CT of face
Bones of middle ear
Tooth primordia
What is in the trunk neural crest?
Dorsal root ganglia and sensory neurons
Sympathetic ganglia
Melanocytes
All pigment cells
What is in the vagal and sacral neural crest?
Para nerves of gut
What is in the cardiac neural crest?
Melanocytes
Neurons
Division between aorta and pulmonary artery
Methods to investigate fate of neural crest tissues
Cell migration stained with monoclonal antibody HNK1
Heterospecific transplantation
What does monoclonal antibody HNK1 do in investigating fate of neural crest cells?
Recognise neural crest cells
What are somites?
Paired blocks of medoserm
How are somites arranged?
Either side of neural tube
How does somitogenesis begin?
Formation of whorls of concentric mesodermal cells marking position of future somites in pre-somitic plate
What does presomitic plate give rise to?
Pairs of somites which differentiate into same cell type but structures formed by them vary
How do structures formed by cells from pairs of somites vary?
Depends on antero-posterior position
What do somites have that is unique?
Positional values
What specifies position values in somites?
Hox genes
What are somites critical for?
Segmental organisation of axial skeleton
What can somites form?
Cartilage of axial skeleton
Muscles of rib cage, limbs and back
Cells that contribute to CT of dermis
What cartilage can somites form?
Vertebrae
Ribs
What determines fates of somite?
Sclerotome
Myotome
Dermatome
What does a somite initially form?
Myoblast
How does a somite convert into a myoblast?
Myoblast determination
What is formed when myoblasts proliferate?
Premuscle mass
What does a premuscle mass form once differentiated?
Myotube
What do premuscle masses differentiate into?
Muscle
What forms neural folds?
Elevation of lateral edges of neural plate
Where does fusion of neural folds begin?
Cervical region
Which direction does fusion of neural folds go?
Caudally and cranially
How is neural tube formed?
Neural folds fuse
How do cephalic and caudal ends of neural tube communicate with amniotic cavity before fusion of neural folds?
Anterior and posterior neuropores
What are initial neural crest cells?
Cells at lateral border of neuroectoderm dissociate
What type of transition will neural crest cells undergo?
Epithelial-to-mesenchymal
Why do neural crest cells undergo transition?
To enter underlying mesoderm
When do crest cells from trunk region leave neuroectoderm?
After closure of neural tube
Which pathways can crest cells from trunk region travel down?
Dorsal
Ventral
What will crest cells from trunk region form if they go through dorsal pathway?
Melanocytes
Where do crest cells from trunk region go through in dorsal pathway?
Dermis into ectoderm via holes in basal lamina
Where do crest cells from trunk region go through in ventral pathway?
Anterior half of each somite
What can crest cells from trunk region form if they go through ventral pathway?
Sensory ganglia
Symp and enteric neurons
Schwann cells
Cells of adrenal medulla
When do crest cells from cranial folds leave neural tube?
Before closure
What do crest cells from cranial folds form?
Craniofacial skeleton
Neurons for cranial ganglia
Glial cells
Melanocytes
What do somites form from?
Presomitic mesoderm
When somites first form, what do they exist as?
Ball of mesoderm
What happens to somites, when they are a ball of mesoderm?
Epithelization
When do cells of somites become mesenchymal?
4th week
What do somites shift their position to?
Surround neural tube and notochord
Which cells form sclerotome?
Somites that surround neural tube and notochord
What do sclerotome eventually differentiate into?
Vertebrae and ribs
Which somite cells form muscle cells?
Cells at dorsomedial and ventrolateral edges of upper regions of somite
Which cells form dermatome?
Cells between sclerotome and muscle forming somite cells
How is dermomyotome formed?
Cells from muscle precursor group become mesenchymal and migrate beneath dermatome
Which cells form most of the musculature of body including limbs?
Cells from ventrolateral edge migrate into parietal layer of lateral plate mesoderm
What do cells in dermomyotome form?
Dermis and muscles of skin of back
Some limb muscles
What specifically does the sonic hedgehog protein induce?
Ventromedial portion of somite to become sclerotome
Main involvement of neural induction
Upregulation of fibroblast growth factor leading to inhibition of BMP4
How does FGF inhibit BMP4?
Upregulates expression of chordin and noggin
WHat happens in the presence of BMP4?
Ectoderm forms epidermis
Mesoderm forms intermediate and lateral plate mesoderm
What do follistatin, noggin and chordain do by inhibiting BMP4?
Induce forebrain and midbrain tissues
What is needed for induction and hindbrain and spinal cord?
WNT3a
FGF
WHat is neuralation?
Neural plate forms neural tube
When are neural folds and neural groove formed?
End of 3rd week
Where does fusion of neural tube begin?
Cervical region - 5th somite
What are neural crest cells?
Cells at the lateral border of the neural ectoderm which migrate as the neural folds fuse
What happens to neural crest cells?
Undergo epithelial-to-mesenchymal transition
When do crest cells from trunk region migrate?
AFter neural tube closure
Along which pathways can neural cells from trunk region go?
Dorsal
Ventral
Dorsal pathway of neural crest cells
Through dermis into ectoderm
What will neural crest cells in dorsal pathway form
Melanocytes in skin and hair follices
Pathway of neural crest cells along ventral pathway
Anterior half of each somite
WHat will neural crest cells in ventral pathway form
Sensory ganglia
Sympathetic and enteric neurons
Schwann cells
Cells of adrenal medulla
When do neural crest cels from cranial region of neural tube migrate?
Before neural tube fuses
What do neural crest cells from cranial region form?
Craniofacial skeleton
Neurons for cranial ganglia
Glial cells
Melanocytes
What does the endoderm give rise to?
Epithelial lining of resp tract, urinary bladder & urethra
Parenchyma of thyroid, parathyroid, liver & pancreas
WHat are somitomeres
Paraxial mesoderm organised into segments
Where do somitomeres first appear
Cervical region
When do somitomeres begin to appear
Beginning of 3rd week
What does each somitomere consist of
Mesodermal cells arranged in concentric whorls around a central unit
How do somites first appear
Ball of mesoderm cells
First stage of differentiation of somites
EPitheliasation
What happens in epithelialisation of somites
Somites arrange around a lumen
What happens to somites in beginning of 4th week
Cells in ventral and medial walls of somite become mesenchymal, losing their epithelial characteristics and surrounding the neural tube and notochord
What do the somite cells which become mesenchyme and surround neural tube and notochord become
Sclerotomes
WHat will these somite sclerotome cells differentiate into
Vertebrae
Ribs
Which cells of somites form muscle cells
Dorsomedial and ventrolateral of upper region of somite
Which part of somite becomes dermatome
Cells between the other groups
Which cells of somites form muscles of body wall and limbs
Ventrolateral edge migrate to parietal layer of lateral plate mesoderm
What forms the dermomyotome
Cells from muscle precursors migrate, become mesenchymal again and go under the dermatome
What do the dermomyotomes form?
Dermis of skin of back
Muscles of back
Intercostal muscles
Limb muscles
Where do signals for somite differentiation arise from
Notochord
Neural tube
Epidermis
Lateral plate mesoderm
What induces ventromedial part of somite to become sclerotome?
Proteins from Sonic hedgehog and noggin genes, produced by notochord and floor plate of neural tube
Four domains of neural crest
Cranial
Trunk
Cardiac
Vagal and sacral
What do cranial neural crests form?
Cartilage
Bone
Cranial neurons
Glia and CT of face
Bones of middle ear
Tooth primordia
What do cardiac neural crest cells form?
Melanocytes
Neurons
Division between pulmonary artery and aorta
What do trunk neural crests form?
Dorsal root ganglia and sensory neurons
Sympathetic ganglia
Melanocytes - all pigment cells of body
What do vagal and sacral neural crests form?
Parasympathetic nerves of gut
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