development of the neural tube Flashcards
(15 cards)
induction in development
One cell population / tissue – the INDUCTOR acts on another tissue – the RESPONDER
This stimulates a specific developmental pathway in the responding tissues
Involves SIGNALLING
induction in development- signals
Protein/peptide growth factors
Ligands binding to receptors, often in the cell membrane
Receptors usually have
Extracellular part
Transmembrane part
Intracellular part
induction in development - signal effects
Signal affects the receptor
Intracellular response is triggered
Signal transduction
Usually involves activation of cytoplasmic protein kinases
Phosphorylate target proteins
Activating or inactivating them
DNA transcription is affected
Cellular response
development of notochord
Transient patterning structure
role in molecular signalling and controlling the direction of embryonic folding.
Flexible rod shaped structure
Ventral to the neural tube
Inductive relationship with overlying ectoderm
In vertebrates, becomes the nucleus pulposus of the intervertebral disc
ectoderm
Appearance of the notochord and mesoderm induces the overlying ectoderm to thicken and form the neural plate
Cells of the plate make up the neuroectoderm and this is the initial event in the process of neurulation
neural plate folding
After plate is induced
Lengthens and lateral edges elevate
Forming the neural folds
Depressed midregion forms the neural groove
The folds approach each other in the midline and fuse
Forming the neural tube
Tube sinks in –overlying ectoderm repairs
Neural tube forms the brain and the spinal cord
mechanisms of bending the neural plate
Number of mechanisms controlling the bending
Cell wedging – microtubules and microfilaments changing cell shape, cell cycle
Hinge points
Median hinge point
Dorsolateral hinge points
Extrinsic forces
Pushing of the surface ectoderm, adhesion point with notochord
closure of the tube
Fusion begins in the cervical region and proceeds in cephalic and caudal directions
Open ends of the tube form the anterior and posterior neuropores
Connect with the overlying amniotic cavity
Closure occurs in week 4, anterior by d25 and posterior by d27
noggin and chordin
Activators of inhibition
Inactivate BMPs – absence of BMP4 causes patterning of neural tube and somites
differentiation of the neural tube (formation of floor plate)
Notochord continues to exert an inductive influence
Presents the signalling molecule Sonic Hedgehog (SHH) to the adjacent neural tube
The ventral-most cells respond to this signal – make the floorplate of the neural tube
Floorplate now makes its own SHH - responsible for the developmentof motor neurones on each side of the tube
sonic hedgehog in other areas
Signal also affects the dermomyotome
- Induces competence to respond to signals from
the surface ectoderm
role of SHH in neural tube bending and closure
During neural tube development, different levels of the spine exhibit different modes of closure – regulated by SHH
In the upper spine, DLHPS are absent due to inhibition by BMP 2. SHH expression is strong which inhibits noggin.
In the lower spine, SHH is reduced. Noggin is un-inhibited and it antagonises BMP2 which allows the DLHPs to form
failure/incomplete closure of the neural tube
Failure in anterior neuropore– anencephaly
Failure in posterior neuropore– spina bifida
Most common in lumbosacral region
treatment of myelomeningoceole
Surgery is usually recommended within the first few hours of life to prevent further damage and infection.
The aim of surgery is to put the spinal cord back into the spinal canal and repair thedamage in the back.
Future surgeries may be required at various points through life
In utero surgery is becoming an option, and is an exciting prospect in paediatrics
diagnosis of neural tube defects
Raised levels of alpha-feto protein
Ultrasound
Folic acid taken prior to conception and in early stages of pregnancy reduces incidence
