General Concepts and Definitions in Developmental Biology - Lecture 18 Flashcards
What does the ectoderm develop into after the gastrula stage?
Nervous system
What does the mesoderm develop into after the gastrula stage?
○ Dorsal (back): notochord
○ Ventral (front): blood, kidney, etc.
What does the endoderm develop into after the gastrula stage?
Internal organs e.g. liver, lungs, etc.
What is descriptive embryology?
○ Experiements which aim to define normal embryonic development without disruption
○ Understanding of what happens during development but not how it happens
What is experimental embryology?
○ Experiments that define how embryonic development occurs
○ Transplantation studies aimed at assessing whether cells or tissues can alter the fate of their neighbours
What did Conklin discover?
○ Mosaic development in tunicate embryos
○ Only some cells inherited yellow cytoplasm
○ Isolated the cells to see what they would develop into (specification map)
○ Found that the fate map and specification map were the same
What did Conklin do with the yellow cytoplasm and what was the result?
○ Pushed it into the cells that would not normally inherit it
○ Results: tissues has muscle cells
○ Confirmed presence of cytoplasmic determinants
What experiments were done on insect embryos?
○ Removing bicoid mRNA (responsible for head development)
- Results: No anterior structures
○ Injecting bicoid mRNA in the wrong location
- Results: head developed in that location
○ Confirms presence of cytoplasmic determinants
What is the fate map of frog embryos at the blastula stage?
○ Endoderm
○ Epidermis
○ Nervous system
○ Blood, kidney
○ Somites, heart
○ Notochord
How does the specification map differ from the fate map for frog embryos?
○ No nervous system
○ No kidneys or heart
○ Uses cell-cell communication
What is regulative development?
The fate of cells is determined by their position in the embryo
What is the evidence that shows regulative development in frog embryos?
○ Cells that form back tissue were transplanted to belly region
- Results: Cells form belly tissue
○ Cells were removed from the emrbyo
- Results: Normal development
What was the baby hair ligature experiments?
○ Hair was used to split the embryo at the two-cell stage
- Results: Two embryos arose from one zygote (half the size)
○ Fate map and specification map are not equivalent at the two-cell stage and it evidence for regulative development
What did Hans Spemann do in relation to the grey crescent?
○ Split embryos so that one half did not have the grey crescent
- Results: only a belly piece formed on one and the other half developed normally
When is grey crescent formed and what is it responsible for?
○ Formed after fertilisation: cytoplasmic streaming
○ Responsible for the notochord
What was the organizer experiment?
○ Grey crescent region was transplanted into the ventral side of another embryo
- Results: Got embryos with two nervous systems
What did the organizer experiment show?
○ Induction of muscle (somites) and neural tissue
○ Dorsal mesoderm is determined by the early gastrula stage
○ Ventral ectoderm and mesoderm are competent to become neural and somitic tissue
What is the 4 signal model of induction events in the early frog embryo?
○ 1. General mesoderm induced from the vegetal pole
○ 2. Nieuwkoop centre present in the dorsal vegetal pole and induces organiser
○ 3. Organiser induces neural ectoderm and induces somites from ventral mesoderm
○ 4. Ventral mesoderm antagonises dorsal vesoderm establishing dorsal-ventral polarity
How does mesoderm arise?
○ Cell-cell communication
○ Animal cap is competent to become mesoderm when induced by vegetal cells
○ Growth factors: FGF and TGFβ family
