Genetic Model Organisms worm mouse 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 Drug addictions Diabetes Obesity

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 Screen and the Segmentation Hierarchy

Biological question Screening assay Speed Specificity Lead to biological insight?

Time table of embryogenesis StageTimeDevelopmental events :00 - 2:10 h Cleavage 5 2:10 - 2:50 h Blastoderm :50 - 3:10 h Gastrulation :10 - 7:20 h Germ band elongation : :20 h Germ band retraction : :00 h Head involution and dorsal closure : :00 h Differentiation

Drosophila embryogenesis 3 h 10 h 22 h Cellular blastoderm Segmented embryo 1st instar larva pole cells (germ line) AnteriorPosterior

Mutant bicoid embryo ab

Mutations in segmentation 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 patterning of 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 ends for integration into genome 2

Syncitial blastodermGerm 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) AnteriorPosterior

The UAS-Gal4 System: How you can make flies with eyes on their legs

x promoterGal4UASgene Gal4 Regulating Gene Activity with Pinpoint Precision progeny flies will express gene in the place of choice

wild-type Misexpression of eyeless using the UAS-Gal4 system

Specialized chromosomes Discovered by Balbiany in 1881 in salivary gland of drosophila larva (3 rd 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 3 rd 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)