What are the stages any embryo goes through?
- Fertilisation
- Cleavage
- Gastrulation
- Neurulation
- Organogenesis
- Adult
What are the desirable characteristics of a model organism?
- Relevance/representative - how similar it is to humans
- Accessibilty/availability
- Easy to experimentally manipulate them
- Good understanding of its genetics
- Cost and space
What are good representatives of humans?
Vertebraes
What are the most widely used models?
- Caenorhabolitis elegans (roundworm)
- Drosophila melanogaster (fruitfly)
- Danio rerio (zebrafish)
- Xenopus laevis (frog)
- Gallus gallus (chick)
- Mus muscularis (mouse)
What are C.elegans?
- Small nematode that lives in the soil
- Easily maintained in lab
- Completely transparent allowing good visualisation of all their body cells
- Short embryogenesis allowing experiments to be carried out quickly
- Very compact genome that has been fully sequenced
- Invariant lineage - all individuals are formed of exactly 558 cells with the origin of each cell being known and traceable
- Development is very precise allowing us to study how specific cellular traits are established during development
What is Drosophila melanogaster?
- Insect so it’s development follows a specific sequence
- Short embryogenesis so many experiments and repeats can be carried out
- Short generation time allows us to assess generational effects of mutations very easily
- Quick and easy to breed
Disadvantage:
-Not transparent so we can’t see how all the different organdie and cell types behave during the 24 hour embryogenesis period
- Low maintenance
- Genetics easily manipulated
What are the Drosophila cuticle patterns?
- Drosophila has larvae and adult forms
- Adults form the embryo which hatches at 24 hours
- Epithelial structures form which are then reorganised to produce structures in adult form (within pupa)
- Drosophila larva has 14 unique segments - each segment has a specific pattern of denticles (each segment has a polarity)
- Anterior portion contains all the denticles; posterior portion contains no denticles
What is Danio rerio (zebraFish)?
- Vertebrae
- Fast embryogenesis
- Short generation time
- Genome has been fully sequenced
- Genetics can be easily manipulated
- Closer to human physiology than invertebrates
- Fully transparent so unbeatable to imagine development at real time
What is Xenopus Laevis?
- Large embryos so easy to manipulate
- Develop in simple salt solution so easy to look after
- Rapid development
- Readily injected with RNA labels
Disadvantages:
- Poorly understood genetics
- Don’t have many tools available to help us manipulate the genome
What is gallus gallus?
- Very big, accessible embryos
- Makes experimental manipulation (grafting, dye labelling) easy
Disadvantages:
-Poor genetics so hard to manipulate genome
What is Dil/Dio fate mapping in chicks?
-This is where specific embryonic cell groups are fluorescently tagged and their final fate is then observed
What is Mus Muscularis?
- Closest model to human as they are mammals
- Morphology and development reorganisation can be well related to humans
- Their genome has been fully sequenced
Disadvantages:
- Develop in utero so hard to access
- Expensive
- Ethical and legal concerns e.g viewing embryo involves sacrificing mother
