Gastrulation and Evo-Devo Flashcards
Does embryonic disc formation precede or follow implantation and gastrulation?
Precedes
What does formation of the embeyonic shield do?
Separates the ICM into the epiblast and hypoblast
What happens to the epiblast?
Becomes two-layered and forms embryo proper
What happens to the hypoblast?
Contributes to yolk sac.
What is a key function of the hypoblast?
Used for positioning the site of gastrulation.
Where is gastrulation initiated?
In the primitive streak
Define gastrulation.
Gastrulation is a critical early embryonic developmental process where a single-layered blastula (or blastocyst in mammals) reorganizes into a three-layered embryo (gastrula), forming the ectoderm, mesoderm, and endoderm,
What determines the location of the primitive streak
Chemical and physical cues
What two proteins are especially important for determining the site of the primitive streak?
Wnt and Nodal proteins
Where does the node of the primitive streak form?
Anterior end of primitive streak
Describe how the node relates to the layer of the gastrula cells will contribute to.
Cells of the upper layer travel to and through the node to give rise to the endoderm and mesoderm, while cells remaining on surface become the ectoderm
In what part of the epiblast does the primitive streak form?
Caudal (posterior) half of the epiblast
What happens at the primitive streak at days 14-15 of development?
Cells invaginate through the streak to form the endoderm
At what day do cells invaginate to form the mesoderm?
Day 16
True or false: Gastrulation is similar in all vertebrates.
True
Outline the changes in cell shape as cells invaginate through the primitive streak.
Epiblast cells are epithelial in structure
Bottle-shaped when in the streak
Mesenchymal in shape as they migrate
What transcription factor is upregulated by invaginating cells?
Snail
What is the function of Snail?
Represses the cell adhesion molecule E-cadherin and activates N-cadherin
How is N-cadherin helpful in gastrulation?
Helps the cells migrate through the prmitive streak
What is the purpose of the epiblast producing hyaluronic acid during gastrulation?
To further promote migration
Describe how hyaluronic acid promotes migration of cells.
Enters the space between the epiblast and the hypoblast and acts as a lubricant.
What is the epiblast?
The embryonic layer that surrounds the other germ layers.
3
What is produced by the ectoderm?
The ectoderm produces the epidermis and forms the brain and nervous system
What is the mesoderm?
The germ layer that lies between the ectoderm and endoderm.
7
What does the mesoderm produce?
Blood
Heart
Kidneys
Gonads
Bones
Muscles
Connective tissues
What is the endoderm?
The germ layer that lies at the most interior of the embryo.
2
What does the endoderm produce?
Epithelium of digestive tube and associated organs, including lungs
What portion of early development seems to be evolutionarily conserved among vertebrates?
Gastrulation
What is the product of gastrulation called?
Pharyngula
Describe the hourglass model of embryo development
Maximum conservation within a phylu, occurs during the middle phylotypic stage, while early and late stages display greater differences
4
Outline Von Baer’s Laws of Vertebrate Embryology.
- The general features of a large group of animals appear earlier in development than do the specialized features of a smaller group
- Less general characters develop from more general, until finally the most specialized appear
- The embryo of a given species, instead of passing through the adult stages of lower animals, departs more and more from them
- Therefore, the early embryo of a higher animals is never like a lower animal, but only like its early embryo.
What does the observation that some developmental forms are conserved across evolution tell developmental biologists?
These stages are very hard to alter
What is evolutionary change based on?
Developmental change
What are homologous structures?
Structures that developed from a common ancestor
Give an example of a homologous structure.
Forelimbs of tetrapods
What are analogous structures?
Structures that share a common function but evolved from independent ancestors.
Give examples of analogous structures.
Wings of birds and bats
