Gastrulation Flashcards
What essentially is gastrulation?
Two layers become three
What does a bi-laminar disc consist of?
Epiblast and Hypoblast
When does gastrulation start?
Beginning of week 3
What happens at the beginning of gastrulation?
Groove and pit form on epiblast along head-tail axis
What is the groove in epiblast?
Primitive streak
What is the pit on epiblast?
Primitive pit and primitive node
What defines anterior pole of embryo?
Anterior visceral endoderm of hypoblast (a.k.a. Anterior hypoblast)
What happens to epiblast cells at beginning of gastrulation?
They divide and stream into embryo from primitive streak/node
How does endoderm start to form in gastrulation?
Some migrating epiblast cells start to replace hypoblast
How does mesoderm form in gastrulation?
Other epiblast cells spread between two layers (epiblast and hypoblast)
What is the notochord?
Specialised rod shaped mesoderm structure
In front of the primitive node at nose-end
What does the notochord form between?
Form between two layers (epiblast and hypoblast) from streams of epiblast cells
What does epiblast become in gastrulation?
Endoderm
What is the notochord important for?
Signalling - to direct development of nervous system
What’s neurulation?
Formation of nervous system
Formation of tube from dorsal ectoderm
What does the primitive node/notochord organise in neural action?
Dorsal structures
What develops in neural action?
Node and notochord release factors that block BMP - drives formation of skin and back/neural tissue
What factors do node and notochord release in neural action?
Chordin
Noggin
Follistatin
What does BMP stand for?
Bone morphogenic proteins
What cells give rise to notochord?
Transplanting node cells
What’s neurulation induced by?
Notochord
What happens to epithelial cells in neurulation?
Become columnar over neural plate
What happens to neural plate in neurulation?
Converts to groove and then a tube
What can be seen on day 20-21 (neurulation)?
Cells on plate edge have thickened to form neural folds and neural groove
What happens on day 22 (neurulation)?
Edges roll over and cells fuse to make a tunnel = neural tube
Actin constricts on apex surface of cells to allow tube to form
What happens on day 25 (neurulation)?
Closure of rostral neuropore (nose direction)
What happens on day 27 (neurulation)?
Closure of Caudal neuropore (tail direction)
What pore will form brain?
Rostral neuropore
WHat pore will form spinal region?
Caudal neuropore
What forms the neural crest?
Specialised cells that have migrated away from the neural tube epithelium
WHat do neural crest cells produce?
Variety of cell types
What essentially is the mesoderm?
Cells that lie between hypoblast and epiblast (third layer)
What happens to cells tha remain in epiblast?
Become ectoderm
WHat are the 3 elements to mesoderm?
Paraxial mesoderm
Intermediate mesoderm
Lateral plate mesoderm
What happens when paraxial mesoderm becomes segmented?
Somites form via clock and wavefront model
What happens when a wave of FGF signal passes along the embryo?
Cells along paraxial mesoderm are programmed to change into part of a somite
What happens if the wave passes cells early in clock cycle?
Become front end of segment
What happens if the wave passes cells late in clock cycle?
Become tail end of segment
Derivatives of paraxial mesoderm:
Somite divides into sclerotome, myotome and dermatome
What structures does paraxial mesoderm form?
Axial skeletal structures
Skeletal muscle
Dermis (dorsal trunk)
Derivatives of intermediate mesoderm:
Kidney and gonads
What structures does intermediate mesoderm form?
Kidney
Urogenital structures
Gonads
Derivatives of lateral plate mesoderm:
Splanchnic and somatic
What structures does lateral plate mesoderm give rise to?
Heart
Blood vessels + blood
Limbs
Spleen
Derivatives of midline mesoderm:
Prechordal mesoderm
Notochord
What structures does midline mesoderm give rise to?
Future site of mouth
What connects yolk sac to gut in endoderm?
Vitelline duct
