General principles of development Flashcards
What 3 things make drosphila melanogaster a good model for development?
- Rapid life cycle
- Small csize
- Genetically tractable
Describe the process of a sperm fusing with an egg
1) Upon contact sperm releases acrosome containing hydrolytic enzymes which break down the zona pellucida
2) Plasma membrane of sperm fuses with that of the egg
3) Initiation of cortical reaction to prevent polyspermy
What is the name of the 16 cell phase and the 58 cell phase?
16 cell - morula
58 cell - blastocyst (has a lumen, can embed in the uterus wall after hatching from the ‘zona pellucida’)
Describe Carnegie stage 6 (13-14 days)
- Is a bilayer embreyonic disc (epiblast and hypoblast)
- Had an amneotic cavity and yolk sac which are all surrounded by te chronic cavity
What is gastrulation?
The movement of cells into the blastula (which becomes the gastrula) to form the mesoderm and endoderm, remainder becomes the ectoderm
What happens in Carnegie stage 7?
Epiblast cells gastrulate to give mesoderm. Notochord tube forms under ectoderm. Disc folds ventrally enclosing some yolk.
What happens in Carnegie stage 8?
The amniotic sac is torn open. Brain folds, neural groove, presomitic mesoderm established, primitive node, primitive streak
What is established in Carnegie stage 6-8?
Axes and the three germ layers
What are the 3 germ layers?
- Ectoderm - epidermis and neurons
- Mesoderm - muscle, tubule cells (kidney), red blood cells
- Endoderm - lung cells, thyroid cells and pancreatic cells
Describe the process of neurolation in a human embreyo
- Called neurula
- Neutral plate folds up around the notochord to form a neural fold joining to form the epidermis and neural tube
- Formation of neural crest
Describe the process of somitogenesis in a human embreyo
- Formation of somites (muscles + skeleton)
- Paired balls of mesoderm form the strips of paraxial mesoderm which flank the notochord
What do the branchial arches and placodes go on to form?
Build face, branchial arches, inner ear, jaw and outer nose
What are the 3 essential steps of development?
- Regional specification
- Morphogenesis (generation of from)
- Cell differentiation
What is polarity?
regional difference in state of commitment
What is a morphogen?
A substance whose variable levels cause
differential responses downstream
How does bicoid work in drosphila melanogaster?
Bicoid mRNA codes for the formation of a head and thorax, and is located to the anterior pole and is translated into protein which spreads towards the posterior forming an anterior-posterior gradient.
What other effect can levels of bcd mRNA have?
Can shift the position of where downstream targets are activated due to various thresholds for multiple downstream genes
How do maternal bicoid levels affect the expression of pair rule genes?
As they activate/repress various downstream gap genes which in turn regulate the pair-rule genes which in turn define boundaries
How is positional information encoded in drosphila?
Hox code determines differentiation pathways
Define compartments
A multicellular region within which the progeny of every cell remain confined
What is an embreyonic field?
An area of embryo/tissue within which a certain process occurs
Why is xenopus laevis a good model?
As its large eggs are amenable to ‘cut-and-paste embreyology’
What are the ‘animal’ and ‘vegetal’ poles of an egg?
Defined before fertilization.
Animal: where sperm enters, more ‘animated’ cell divisions
Vegetal: Rich yolk with fewer divisions
What are the stages of xenopus laevis embreyogenesis?
- Fertilisation
- Cleavage (division without growth)
- Formation of gastrula with 3 germ layers
What is induction?
- The process by which one embreyonic region interacts with a second embreyonic region to influence the second region’s differentiation or behavior.
- Can come from other cells or the environment
- Signal can be ‘instructive/directive’ or ‘permissive’
What are the 3 methods of induction?
- Diffusion - signal form one cell interacts with a receptor on a target cell
- Direct contact - interaction of transmembrane proteins
- Gap junction - movement of signals between connected cells
What is specification?
If a tissue/cell explant develops autonomously into a particular structure after isolation from the embreyo
What is fate?
The final state of cells of tissue during normal development
Change over time
What 3 methods can be used to create a fate map?
- Use dyes such as Nile Blue/fluorescently labelled dextrans
- Transplantation of pigmented into albino tissue
- Fluorescently tagged protein
What is determination?
Progressive restriction in developmental potential of different cell types
What is acquisition of commitment via lineage?
When the state of commitment of a cell is inherited from its determined parent cell
What is mosaic is?
When the map of specified regions (determined independently of each other) exactly match the fate map
What is regulation?
When the specification of isolated parts does not correspond to the fate map
What is a stereotypical cell lineage?
When we can name each cell and see exactly what it came from and what it becomes
