9 - Embryogenesis and Development II Flashcards
Neurulation (Organogenesis)
the formation of the neural tube that is the basis for the nervous system
neurulation process
- Notochord develops from dorsal mesoderm
- Induction of neural plate from ectoderm layer above the notochord
- A neural groove and neural folds form from the dorsal ectoderm
- The neural folds rise up, meet and fuse to form the neural tube
- The neural tube becomes the central nervous system (brain and spinal cord).
the neural crest
● Specialist migratory populations
● Migrate on cranial, dorsolateral and ventral pathways
● Highly migratory, invasive and proliferative
● Include melanocytes (called melanoblasts in embryo) and cells that form the adrenal medulla
What are the different types of crest cells?
- Cranial NC: cranial neurons, facial mesenchyme.
- Cardiac NC: tissue wall of large arteries.
- Trunk NC: dorsal root ganglia- sensory, adrenal medulla, pigment cells.
- Vagal NC: parasympathetic ganglia.
- Include melanocytes (called melanoblasts in embryo) and cells that form the adrenal medulla.
neurulation in chicks
The archenteron forms when lateral folds pinch the embryo away from the yolk.
The notochord, neural tube and somites develop much like in the frog.
By 3 days, and 2-3 mm in length, rudiments of most major organs are visible.
What happens in neurulation of amphibians?
- Once the meso-, ecto- & endoderm are formed, they begin to thicken around the dorsal blastopore region.
- The cells start to stretch & grow + a neural plate is created.
- The edges of this neural plate are the normal ectoderm (any tissues are ectoderm).
- The neural plate is in the centre and the fold in the middle causes the sides to go upwards. Multiple folds along the middle allow a tube to be made.
- The end result is an undisturbed layer of ectoderm with a neural tube sitting underneath it.
What happens in neurulation of humans?
- Initially, there is a neural plate with neural crest cells on the edge, and the epidermis.
- A medium hinge point and 2 dorsal lateral hinge points (side folds) are made, creating a tube.
- Convergent extension allows for lots of cells come together and line up for optimal reorganisation to give a long tube.
- Cells grow and become really tall to thicken the plate in apical constriction.
- The cytoskeleton changes shape so that you create an apex, making bottle-shaped cells, creating a hinge.
- In localised regions, these triangular shapes pull the tissue in and around.
Induction
where the fate of one cell is influenced by another
• This can occur over a long distance, involving diffusible molecules, or between adjacent cells, involving cell surface molecules.
How are human blastocysts formed via cell signalling?
- Cellular communication, both long range, and short range can create complex positional information.
- Contact with surrounding cells, with underlying tissues and responding to signals from neighbouring or distant cells, can affect how a cell will behave.
- Cells on the outside of a blastocyst have contacts on 2 sides, which ‘tells’ them they are on the outside.
- Cells in the ICM have more contacts, defining them as ‘inner’.
- If you move them at early stage the cells will change identity.
- If you move them later on, cells will ‘remember’ what they are supposed to be.
What is cell autoregulation?
- Cells can react to their own signals, or to signals from neighbouring cells.
- This local signalling can be inhibitory or inducing, i.e. preventing or stimulating a pattern of gene expression.
Spemann organizer
a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system
how the organiser alters cell fate
- MP-4 is uniformly distributed in late blastula and causes VENTRAL development.
- Chordin and Noggin (secreted by organiser) stop action of BMP-4 and allow dorsal development e.g. muscle and notochord (dorsal mesoderm)
Induction of the neural plate
the phase of neural development during which the neural plate has a groove that becomes a tube
apical ectodermal ridge (AER)
at tip of bud; secretes Fibroblast growth factor that extends limb bud
zone of polarizing activity (ZPA)
Controls anterior-posterior digit formation via induction.
