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Lecture 4
• Mosaic analysis
• Maternal/zygotic screens
• Non-complementation screen
• Cytogenomics to genomics
• Designer deletions
• Gene disruption in Drosophila
• Systematic RNAi screens
Lab 4 schedule• MONDAY SECTION: Sunday 9:30-11:30
AM come in to start your in situ. WSC 339
• TUESDAY SECTION: Monday 10-12AM come in to start your in situ. B&G 3015
• On Monday and Tuesday the lab B&G 3015 will be open at 10AM to start your washes.
Flip mediated site specific recombination
Yeast two micron plasmid
A
B
C
D
A
B C
DFlip
FRT
FRT FRT
FRT
Mosaic analysis
• Assay adult phenotype of an embryonic lethal.
• Determine the site of action of a gene product.
• Analyze Zygotic lethal/Maternal effect mutants.
+Bal
+Bal
Zygote Oogenesis
Pure zygotic screens
Assume pure expression of a genefrom the zygotic genome only.
+Bal
Zygote
Oogenesis
Maternal Rescue
The maternally suppliedtranscript rescues the zygotic loss of function.
Maternal Rescue
Hide an essential role for a gene in embryonic pattern formation.
Pure zygotic screens may miss important functions.
+Bal
+Bal
Zygote Oogenesis
Zygotic lethal/Maternal effect
Dies atlatelarval stageor pupal stage
We can not assay if the gene hasa maternal effect phenotype.
Zygotic lethal/Maternal effect
Since a homozygous adult mothercan not be established, we can notassay whether the gene contributesinformation to the egg.
Screen for maternal rescue and zygoticlethal/maternal effect
1/2 to 2/3 of lethal mutations are notembyonic lethal.
Norbert Perrimon collected a large #of late larval and pupal lethals.
Maternal rescue vs. Maternal effect
Maternal rescue can be rescued by thepaternal allele.
Maternal effect is independent of thegenotype of the sperm.
Non-complementation screen
en1/en1 engrailed phenotype
en1/deletion engrailed phenotype
en1/+ wild-type phenotype
en1/enx
Non-complementation screen
CyO/L virgin females X b pr cn males
en1/en1 virgin females X b pr cn*/CyO
Screen vials for flies with the en phenotype
F0
F1
F2
EMS
4,000 crosseswith individual males
Vials with no engrailed flies
Vials with engrailed flies
en1
CyO
en1
CyO
b pr en+cn* en1
b pr enxcn en1
50% 50%
50% 50%
Drosophila genome
• 2000 first draft of genome published
• More than 200,000 expressed sequence tags available
• Large scale transposon mutagenesis
• Flybase: computer database and resource
Flybase and Modern Drosophila Research
1. No longer have to clone and sequence a gene- reagents readily available.
2. Store of characterized mutants. RNAi
3. Large scale genome screens like 2 hybrid analysis and insitu hybridization are available.
4. Allows researchers to propose and formulate questions with data available.
RNAi in Drosophila
1.) Cell culture RNAi. Any Drosophila gene’s expression can be reduced in cell culture.
2.) RNAi transgenes in flies. 88% of the annotated genes of Drosophila represented in this collection of fly stocks.
RNAi in Drosophila
RNAi in Drosophila is cell autonomous ie where the RNAi is produced is where the effect will be.
C. elegans RNAi is systemic--non cell autonnomous. Can enter the worm via diet.
Binary or two component system
Fly stock A: UAS line Fly stock B: Driver line
RNAi
GAL4 binding sitesUASGAL4
GAL4Promoter
or Enhancer
RNAi GAL4
Progeny
GAL4