genetic model organisms
DESCRIPTION
mouse. worm. Genetic Model Organisms. fish. yeast. fruit fly. weed. Drosophila melanogaster Genetics and Developmental Biology Physiology and Behavior Many disease-causing genes in humans have corresponding homologues in the fly genome Cancer Neurodegenerative disease - PowerPoint PPT PresentationTRANSCRIPT
Genetic Model Organisms
worm mouse
fish
yeast
fruit flyweed
Drosophila melanogasterGenetics and Developmental BiologyPhysiology and Behavior
Many disease-causing genes in humans have corresponding homologues in the fly genome
CancerNeurodegenerative diseaseDrug addictionsDiabetesObesity
Life cycle of Drosophila
• embryogenesis • three larval stages • a pupal stage • the adult stage
Groups of cells called imaginal discs are set aside at specific sites in the larval body. From these the various body parts develop during pupation (adult muscle, the nervous system, etc).
• A relatively short life cycle (10 days)• Culturing flies is cost-effective (vs mice)• A variety of genetic and molecular tools
available (functional testing in vivo)• Complete genome sequence (13,500
genes)
Advantages of the fly system
• A relatively short life cycle (10 days)• Culturing flies is cost-effective (vs mice)• A variety of genetic and molecular tools
available (functional testing in vivo)• Complete genome sequence (13,500
genes)
Advantages of the fly system
(A)Bridges (left) and Sturtevant in 1920 (B) Morgan in 1917
Thomas H. Morgan and the Caltech fly group
Nüsslein-Volhard and Wieschaus (along with Edward Lewis) were awarded the 1995 Nobel Prize for Physiology/Medicine.
(1980)
Christiane Nüsslein-Volhard, Eric Wieschaus and the Baden fly group
Saturation Mutagenesis Screenandthe Segmentation Hierarchy
Biological question
Screening assay
Speed
Specificity
Lead to biological insight?
Time table of embryogenesis
Stage Time Developmental events
1- 4 0:00 - 2:10 h Cleavage
5 2:10 - 2:50 h Blastoderm
6 - 7 2:50 - 3:10 h Gastrulation
8 - 11 3:10 - 7:20 h
Germ band elongation
12 - 13
7:20 - 10:20 h
Germ band retraction
14 - 15
10:20 - 13:00 h
Head involution and dorsal closure
16 - 17
13:00 - 22:00 h Differentiation
Drosophila embryogenesis 3 h
10 h
22 h
Cellular blastoderm
Segmented embryo
1st instar larva
pole cells (germ line)
Anterior Posterior
Mutant bicoid embryo
a b
Mutations insegmentation genes
Maternal genes
Gap genes
Pair rule genes
Segment polarity genes
Segmentation Hierarchy
Molecular Cloning of Genes
What is the gene product?
Where and when is it active?
Was the genetic prediction correct?
Molecular Mechanisms
Segmentation fate map of Drosophila embryo
Drosophila early development
ftz (fushi tarazu) gene expression pattern
Ernst Hafen and Walter Gehring (1983)
in situ hybridization (RNA detection) need probe!
even-skipped (blue), ftz (red)
antibody staining (protein detection) need antibody!
hunchback (blue) and Krueppel (green)
Gap Genes
Fluorescent staining
Molecular patterningof the embryo
Bicoid (blue) Even skipped (red) Krüppel (yellow)
Segmentation Hierarchy
Biological question
Screening assay
Speed
Specificity
Lead to biological insight?
Germ-line Transformation and in vivo Genetic Manipulations
Is the striped expression of ftz really necessary?
What happens if you express ftz everywhere?
How would you test this?
For example...
Heat shock promoter-ftz P-element plasmid
Adapted from Wang and Lin, 2004
transformation
ftz
1
Transposase (“helper”) plasmid acts on P-element endsfor integration into genome
2
Syncitial blastoderm Germ cells
Transposable P-element mediated transformation
Allan Spradling and Gerald Rubin (1982)
Drosophila embryogenesis 3 h
10 h
22 h
Cellular blastoderm
Segmented embryo
1st instar larva
pole cells (germ line)
Anterior Posterior
The UAS-Gal4 System:
How you can make flies with eyes on their legs
xpromoter Gal4 UAS gene
Gal4
Regulating Gene Activity with Pinpoint Precision
progeny flies will expressgene in the place of choice
wild-type Misexpression ofeyeless using theUAS-Gal4 system
Specialized chromosomes
Discovered by Balbiany in 1881 in salivary gland of drosophila larva (3rd instars)
Why salivary gland of drosophila larva will
have Polytene Chromosomes????????????????
Polytene chromosomes
Drosophila Polytene chromosome
Drosophila Karyotype
1933, Painter showed the banding pattern in Drosophila
1935, Bridges
Banding pattern is fixed in a particular chromosome in a particular species
Polytene chromosome is found in 3rd instar larva of Diptera
Also found in
Malpighian tubules
Mid Gut epithelium
Rectum
Of Diptera order of insects
And in ovary of some plants
wildtype obese (leptin)