Drosophila melanogaster

Source: Zdenék Berger

Mating

Egg-laying

Embryo

larva

pupa

adult

Life Cycle

(10 days)

Drosophila natural history• Originated in Africa• Probably spread by human activity• Now found most places where we live• Likes compost, rotting fruit, yeast• Some features conserved, others a reflection of its life

strategy• Harmless (mostly)• Most lab strains derived from isolates collected before 1940’s• Strains collected subsequently have P transposable elements

and can’t easily be used

Model Organisms - a trainspotter’s guide

E. coli Yeast Worm Fly Mouse Human

# Genes 4000 6000 19000 15000 30000? 30000?

Genome (Mb) 4.6 150 3000 300010012

# Neurons 0 (1) 302 105 1011

Where our pet flies live…

Mice - 75c/day150k$/yr

Flies ~ 20k$/yr(consumables and labour)

Can’t be stored frozen :-(Source: John Roote

What are flies useful for?

Fly pushingEarly 1900’s - Drosophila contributes to our understanding of heredity

Mid 1900’s - Grows in popularity among developmental biologists

Homozygous lethal mutations can be kept indefinitely as heterozygous balanced stocks

1970’s - 1980’s - Molecular biology, cloning of Hsp, Hox

1970’s - 1980’s - Large screens for developmental mutants

1982 - Transformation by injection of marked P transposable element into syncytial embryos; transgenic flies identified by marker in F1

1988 - Easy mobilisation of P made possible by stable transposase-producing strains

Recent articles from PubMed

C.J. O’Kane (2003). Seminars in Cell and Developmental Biology 14:3-10. Source: Claude Everaerts

What’s different?

• More gene redundancy in humans & mammals

• Some organisation of tissues and organs

• Cardiovascular system

• Acquired immunity (antibody response)

• We’re studying them, instead of them studying us

Insertional mutagenesis: many ways to kill a gene…

Fly Gene Disruption Projects• Based on transposable element insertion

• Allows further local mutagenesis

• Non-directed - like Venter’s sequencing strategy

• Not random

• ~ 15000 target genes

• include ~ 4000 vital genes

• Requires ~ 1 insertion per 8 kb

• Coverage perhaps 25% of that, more on their way into public domain

FlyBasewww.flybase.org

Other ways to make “mutants”

• EMS - still has its attractions• Targeted knockouts for reverse genetics• Imprecise excisions for reverse genetics• RNAi for reverse or forward genetics• Deletion kits in defined backgrounds• Ask a fellow flypusher

Getting round early lethality

• GAL4 x UAS-X for targeted expressionCan be used for regulated RNAi expression

GAL4 enhancer traps

Getting round early lethality

• GAL4 x UAS-X for targeted expression• Enhancer/suppressor screens

Identifying genes in receptor tyrosine kinase signalling - screening for enhancers of sevenlessts

Getting round early lethality

• GAL4 x UAS-X for targeted expression• Enhancer/suppressor screens• Mitotic clones (using FLP recombinase)

Mutant screens using mitotic clones

Getting round early lethality

• GAL4 x UAS-X for targeted expression• Enhancer/suppressor screens• Mitotic clones (using FLP recombinase)• Temperature-sensitive point mutations• RNAi screens in cultured cells

Shared biology - shared diseases

• Cancer

• Ageing

• Neurodegeneration

• Infectious disease

• Models for disease vectors

• Behaviour

• Do flies have disease-gene homologs?

• Do flies have basic cellular processes related to the disease?

• Be nice to a friendly fly geneticist

Flies and “your” disease

The future?

• More insertions• UAS-RNAi collections• SNPs, better mapping of point mutations• Temperature-sensitive alleles for cell biology• Screens take more work in flies than in worms• Some things only possible in flies and not worms -

physiology, some development, some cell biology• “Hopping in” takes about $20k investment, or a

friendly fly lab to drop in on