01-11-21 - Gastrulation and Neurulation Flashcards
Learning outcomes
- Understand the sequence and significance of gastrulation
- Explain the formation of the neural tube during neurulation
- Be aware of the origin of neural crest cells and the diversity of their derivatives
- Be aware of origins and main derivatives of ectoderm, mesoderm and endoderm
What are the structures present on the epiblast of the embryo at the beginning of week 3 after fertilization?
What is the head of the embryo called?
What does this structure establish?
How does the shape of the embryo change as time goes on from here?
- On the epiblast (dorsal surface) of the tail end of the embryo, groves with raised edges form, which forms the primitive streak along the head-tail axis
- This primitive streak leads to the primitive node, which is a pit
- The head of the embryo is called the anterior (rostral) visceral endoderm, even though no endoderm has formed yet – this structure defines the anterior pole of the embryo
- The embryo elongates from this point
What occurs during gastrulation?
What are the 3 steps that form the endoderm?
How is the ectoderm formed?
How is the mesoderm formed?
How is the notochord formed?
Where is the notochord formed?
What is the notochord?
What is the function of the notochord?
What is it involved in the development of?
How does the ectoderm form?
What do all these processes form?
- During gastrulation, the formation of the ectoderm, mesoderm and endoderm takes place.
- Endoderm formation:
- Epiblast cells from the primitive streak begin to divide and move away from the primitive streak.
- Some of these epiblast cells begin to replace the hypoblast cells, eventually replacing them completely
- These cells are called true endoderm cells, and transform the hypoblast completely into endoderm
- Epiblast cells come from the tail end of the embryo, and stream laterally and forward to form the mesoderm by spreading between the epiblast layer and the forming endoderm layer
- Mesoderm cells forming at the primitive node stream laterally and forwards, and burrow between the epiblast layer and the forming endoderm layer, which forms the notochord
- The notochord is formed at the nose-end (rostral) Infront of the primitive node, and is formed along the head-tail axis of the embryo
- The notochord is a rod-like condensation of mesoderm
- The notochord is an important signalling structure, and is directly involved in the development of the nervous system
- The ectoderm is formed by epiblast cells that stay in the epiblast, which doesn’t require much migration
- These processes together form the tri-laminar disk
What does the histology of the formation of the tri-laminar disc look like?
What are ventral structures?
What are dorsal structures?
What are some ventral structures made in the embryo?
What signals their development?
What organises dorsal structures formation?
How do these structures do this?
What is an experiment regarding this process?
- Ventral structures refer to the front of a structure
- Dorsal structures are relating to the back or posterior of a structure (posterior) e.g the spine
- The skin / ventral belly (around stomach area) are ventral bodies
- Their development is signalled by BMPs (bone morphogenic proteins), which are potent stimulators of bone formation and other cellular functions
- The organisation of dorsal structure formation is done by the primitive node (pre-cursor)/notochord
- These structures release factors (chordin, noggin, follistatin) which blocks BMP
- This allows for the development of back/neural tissue to take place
- During the Spemann and Mangolds experiment, node cells were transplanted into an embryo, which resulted in 2 dorsums forming (back structures)
What is neurulation?
What is neurulation induced by?
What occurs to the epithelia over the neural plate?
What changes does the neural plate undergo during this process?
When is the initial change noticeable?
- Neurulation is the process of turning the flat neural plate into the neural tube
- Neurulation is induced by the notochord, which is deep to the neural epithelium
- The neural epithelium over the neural plate become columnar
- The neural plate converts to a groove then a tube, with the initial midline neural groove apparent after day 19
What occurs in neurulation after 20-21 days?
- During neurulation after 20-21 days, the embryo has elongated
- The cells on the neural plate edges have thickened, forming neural folds and a neural grove
- The neural folds are now starting to come close to each other
What occurs during neurulation from day 22 into the 4th week?
- During neurulation from day 22, the neural cells of the neural cells fuse together to make a closed tube.
- The curvature of the tube is driven by chances in the actin of the cytoskeleton in the apical area of cells
What occurs in neurulation in day 25 and day 27?
What conditions occur if these pores fail to close?
- During neurulation on day 25, the rostral neuropore in the nose direction of the embryo closes, and the brain is formed from 3 vesicles in this region
- On day 27, the caudal neuropore in the tail direction of the embryo closes and the spinal cord begins to develop
- Failure of closure of the rostral neuropore results in anencephaly, where the brain is not developed properly
- Failure of closure of the Caudal neuropore causes some forms of spina bifida
What are neural crest cells derived from?
What changes do neural crest cells undergo?
Where do they migrate to?
- Neural crest cells are derived from the edges of the neural tube
- Neural crest cells undergo an epithelial to mesenchymal cell transition (EMT)
- The migrate from the neural tube into the embryo
What are the various cell types derived from neural crest cells?
What are the neural crest cell defects associated with dalmatians?
- Dalmatians have defects in the development and migration of melanocytes, which is what causes their colour
- Dalmatians are often deaf, meaning there is problems with their cranial nerve ganglia
How common is Waardenburg’s syndrome?
What is it caused by?
What are 4 symptoms of Waardenburg’s syndrome?
What can other types present with?
- Waardenburg’s syndrome is 1/50,00 chance
- It is caused by transcription factor problems
- Some types are caused by Pax-3 deletion
- Symptoms include:
- Pigment abnormalities (even albinism)
- Deafness
- Heterochromia of eyes (different eye colour)
- Telecanthus (widely separated eye corners – craniofacial issues)
- Other types of Waardenburg’s syndrome can also show additional constipation (SOX 10 – autonomic ganglia failure)
How common is Treacher Collins Syndrome?
Where is this mutation found on chromosomes?
What is it caused by?
What are 5 symptoms Treacher Colins Syndrome presents with?
- Treacher Collins Syndrome is 1/50,000 chance
- It is an autosomal dominant condition
- It is caused by a defective protein called treacle (TCOF1) gene
- Symptoms of Treacher Collins Syndrome:
- Abnormal eye shape
- Conductive hearing loss
- Micrognathia (abnormally small jaw)
- Underdeveloped zygoma (bone in the face)
- Malformed ears
During gastrulation, what are the 3 layers of mesoderm that form?
What does the lateral plate mesoderm do?
What 2 layers does the later plate mesoderm form?
What do these layers do? Where is the notochord located?
Why is this expected?
- In the mesoderm, the 3 layers that form are:
- The lateral plate mesoderm]
- The intermediate mesoderm
- The paraxial mesoderm (close to body axis)
- The lateral plate mesoderm coats the embryo and forms:
- An inner visceral portion (splanchnic) – this will coat the forming gut tube from the yolk sac
- An outer parietal portion (somatic) – will form the internal body wall of the embryo
- The notochord is located under the neural tube
- This is expected, as the notochord pushes cells to generate the nervous system
What happens to the paraxial mesoderm?
What is the model that does this called?
Describe the 6 stages of this model.
What does this model explain?
- The paraxial mesoderm becomes segmented into somites
- Somite formation is from the clock and wavefront model
- Clock and wavefront model:
- Cells in the paraxial mesoderm have a clock cycle that they go through every 90 minutes
- As they go through this process, the back of the embryo is elongating via the wavefront moving backwards
- While the Wavefront moves backwards, it passes over the paradoxical mesoderm and releases FGF (signalling factor)
- If the wavefront passes across cells that are early in their clock cycle, they will make the head of the somite
- If the wavefront passes across cells that are in the middle of their clock cycle, they will make the middle of the somite
- If the wavefront passes across cells that are late in their clock cycle, they will make the tail of the somite
- This process explains why there can be hundreds of somites in a particular organism
What 2 things does the paraxial mesoderm form?
What do these then form?
- The paraxial mesoderm forms:
- Head
- Somites
- Somites form:
- Sclerotome - Axial skeletal structures e.g vertebrae and ribs
- Myotome - Skeletal muscles
- Dermatome - Dermis of the dorsal trunk – structures, including muscle and bones, which define the back
What 3 things does intermediate mesoderm form?
- The intermediate mesoderm forms:
- Kidneys
- Urogenital structures e.g ureters (concerned with reproduction and urinary excretion)
- Gonads
What are the 2 layers of the lateral plate mesoderm?
What 5 things do they each form?
- Splanchnic (visceral) lateral plate mesoderm
- Viscera coverings – covers of soft internal organs of body
- Heart
- Blood vessels
- Blood
- Spleen – organ in the upper left of abdomen, part of immune system
- Somatic (parietal) lateral plate mesoderm
- Body wall
- Limb cartilage
- Limb bone
- Limb dermis
- Lateral/ventral trunk dermis - structures, including muscle and bones, which define the sides and front
How much is left of the midline mesoderm?
What 2 things does the midline mesoderm form? What do these form?
- There is not much left of the midline mesoderm
- Midline mesoderm forms:
- Notochord – forms nucleus pulposus (inner core of vertebral disc)
- Prechordal mesoderm – future site of mouth (prechordal mesoderm + associated endoderm = prechordal plate)
What is the full mind map of derivative of the mesoderm?
When does embryo folding begin?
How does it initially fold?
What occurs in this folding?
What is formed?
How does the embryo then fold?
What goes this form?
- Embryo folding occurs after 17 days
- Initially there is cephalocaudal (head-tail) folding
- During this folding, the lateral plate mesoderm and amniotic cavity folds around, and pinches off part of the yolk sac (endoderm origin)
- This forms the GI tube (gut tube) running from mouth to anus
- Lateral folds of the embryo close the body wall (formed by parietal lateral plate mesoderm), and forms cavities in the embryo
- These cavities will eventually form the various cavities in the body e.g pleura, pericardium, abdomino-pelvic cavity
What the starts to form in the gut tube?
What is the vitelline duct?
What happens to it?
What is remnants of vitelline duct known as?
What can it cause?
What is the cloaca?
What happens to it?
What is then formed?
What connections are then made?
- Organs start to form as buds from the gut tube (endoderm) e.g stomach, liver pancreas, lungs
- The vitelline duct is a connection from the embryo to the remnants of the yolk sac that was pinches off during folding
- After 5-6 weeks, the vitelline duct is usually obliterated, and forms the future ileum
- Remnants of the vitelline duct is called Meckel’s diverticulum, and is present in 2% of the population
- This can cause symptoms such as bleeding
- The cloaca is a shared space in the endoderm
- It closes off to form the rectum and urinary bladder
- The urinary bladder will join up with tubes that come from the intermediate mesoderm in the kidneys (the ureters)
What are the derivatives of the ectoderm?
