What is gastrulation?
Cell migration that leads to the development of germ layers
- Amphioxus (vertebrate common ancestor): develops germ layers by folding the whole embryo
Amphioxus - elongation and tissue movement through cell division
- Dividing mesoderm cells accumulate up and around the blastopore -> end up on the dorsal side surrounding the blastopore next to the notochord
- Notochord moves laterally and squishes blastopore in the middle until the blastopore is on the ventral side
Tubes and segments form through folding, sealing, and pinching off
Internal folds/pinch-offs make 3 major types of tubes (mesoderm, neural tube, and gut)
Describe process of folding/sealing/pinching off
- Endoderm begins curve towards itself and the notochord comes towards that curving (ventrally)
- Mesoderm (on lateral sides and just dorsal to endoderm) begins to fold onto itself to make somites
- Notochord and endoderm then attach and pinch together further all while the neural plate moves ventrally and starts to pinch itself dorsally
- Notochord and endoderm pinch off forming gut (endoderm) and the notochord remains attached to the endoderm dorsally
- The neural plate forms the neural tube dorsal to the notochord
- Somites spread laterally and ventrally
Mesoderm segment (somite)
- Formation occurs anterior to posterior
- Neural tube stays open for now
Vertebrate development added complexity is?
- Amphibian blastula has yolk-filled endoderm precursor
- Develops germ layers through involution
Describe vertebrate development process with that added complexity
- Cells near animal pole migrate faster, resulting in the blastopore moving dorsally
- Mesoderm precursors form near the ventral lip of the blastopore
- Notochord precursor cells travel along the outer surface (ectoderm), dive into the blastopore, and then travel along the inner surface
- Mesoderm travels all over lateral and ventral inner surfaces
Vertebrate Neurulation
Produces neural crest cells that migrate all over the body, where they go to initiate the development of body systems and become part of them. Unique to vertebrates.
Mesoderm division (parts and what they become)
- Intermediate mesoderm: reproductive and kidney systems
- Paraxial mesoderm: skin/skeletal/skeletal muscle formation
- Somatic lateral plate mesoderm: body cavity linings and limbs or fins
- Splanchnic lateral plate mesoderm: associates with endoderm to become gut, also becomes circulatory system
Disk-shaped embryos follow the same steps - gastrulation, folds, and segment
- Reptiles, birds, and mammals start with a disk-shaped embryo
- Primitive streak: groove where cells dive into embryo on dorsal side
- 3 layers stacked on each other after
Ectoderm becomes:
- Skin, feathers, scales
- Brain and spinal cord
Paraxial mesoderm becomes:
- Skeleton
- Skeletal muscle
Intermediate mesoderm becomes:
- Urinary system
- Reproductive system
Splanchnic mesoderm becomes:
- Associates with endoderm to become the digestive system
- Heart and circulatory system
Endoderm becomes:
- Digestive system
- digestive and respiratory linings
Neural crest
- Critical for head and pharynx development
- Travel throughout body in 3 major streams: anterior to posterior: 1) Trigeminal (around eye) 2) Hyoid 3) Branchial
