Lecture 7 - Early Development I: introduction to Drosophila Flashcards
(32 cards)
Why are model organisms used in development?
- Eggs have the information to create whole to create a whole organisms.
- Nevertheless, the methods used to create organisms are conserved. This allows the use of model organisms.
How do you build a complex animal from a single cell?
We can study the development of different genetically tractable animal models to tackle this question.
What are pros and cons of rodents?
Pros - good genetics well established model
Cons - expensive, slow, home office/ethical restrictions
What are the pros and cons of chick?
Pros - accessible embryology, low cost
Cons - no genetics, can’t really work on adults, ethical restrictions
What are the pros and cons of zebrafish?
Pros - accessible embryology, reasonable cost
Cons - genetic problematic homo office/ethical restrictions
What are the pros and cons of Drosophila melanogaster?
Pros - easily controlled in tubes, accessible embryology and adult developmental stages, very low cost, fast, excellent genetics, limited ethical concerns
Cons - not a vertebrae, kept as live stocks
What is there for every organ in humans?
For almost every organ in humans there is a match in flies.
Common genes underlie their patterning, development and organisation.
How are flies stored?
Flies are cheap and have a rapid life cycle. Flies kept as live stock kept at 25 degrees Celsius or 18 degrees Celsius
What is the life cycle of Drosophila melanogaster?
Fertilised egg - cleavage - Syncitial blastoderm - gastrulation - hatching - 1st instar- 2nd instar -3rd instar (Larva) - pupa - metamorphosis - adult fly
What mutant fly was found first?
Fly with white eyes (w)
What was the Heidelberg Screen?
2 researchers undertook a saturation mutagenesis to identify genes involved in the development and patterning of the larval cuticle. Use to explore the gradual process in the embryo in how the elaboration of patterning of cell differentiated was achieved.
The screen involved:
- mutagenising flies by feeding males a potent mutagen - EMS (Ethyl methane sulfonate)
- Analysing cuticle preps for patterning defects.
What is a cuticle prep?
Flies’ embryos don’t have bones, but their skin secretes a cuticle to maintain structure.
How much EMS was used on the flies?
Used low dose of mutagen with the aim to create mutation in only 1 gene, but in all genes around all flies.
What was involved in Drosophila gene naming?
Wanted a simple description of the phenotype
- Avoid names suggesting an interpretation of the function of the gene
What are technical & methological advances?
P-element transformation - transgenics
Enhancer trap - promoter trapping
Gal4/UAS - gene misexpression
FLP/FRT - ‘clonal’ mutant analysis
RNAi & CRISPR - both ex vivo & in vivo
Omic technologies - genome, transcriptome, proteome etc.
A range of techniques that use transgenic animals to either visualise, misexpress or reduce gene expression.
What % of human diseases are shared with flies?
75%
How many offspring come from 2 parents (male & female)?
200 offspring (in less than 2 weeks)
Where does patterning start?
In the mother (egg) - oogenesis - mothers already initiate embryonic patterning
Describe oocyte fertilization
- females only need to mate once
- seminal receptacle stores sperm
- eggs ‘drilled’ into food when laid
What do Nurse cells do?
- important for oocytogenesis
- endo-reduplication (DNA replication without cytokinesis - cell division)
- many copies of the genome
- supply RNAs/Proteins to the egg
- Maternal contribution
What are maternal contributions?
- proteins & RNAs made in nurse cells
- transferred into developing oocyte
cytoplasmic dumping (via ring canals)
Maternal contribution sets up the major axis in the future embryo
Where is bicoid mRNA found?
in the anterior of the embryo
- microtubule transport
- minus + plus ended motors
- ‘glue’ anchors them in position
Where does the sperm enter through?
micropyle (does not play a role in patterning)
What is the chorion?
egg shell, secreted by the follicle cells
