Zebrafish in genome research

Can you spot the difference?

What is a zebrafish?

• Danio rerio• Small freshwater fish

from South Asia.• 4 cm long when fully

grown.• Common aquarium

fish.• Very easy to look after.

Image: Wikimedia commons/Marribio2

What is a model organism?

• Non-human species widely studied to understand human disease.

• Model organisms are used when experimentation using humans is unfeasible or unethical.

• Can you think of a model organism?

Types of model organismGenetic model organisms Experimental model

organismsGenomic model organisms

Good candidates for genetic analysis.

Good candidates for research into developmental biology.

Good candidates for genome research.

Breed in large numbers.

Have short generation times so large scale crosses can be followed over several generations.

Produce robust embryos that can be easily manipulated and studied.

Easy to manage genomes e.g. small genome size or limited number of repeats.

Genome is similar to a human.

Images: Wellcome Trust Sanger Institute

Why use zebrafish?

• Small size.• All major organs present

within 5 days post fertilisation.• Short generation time

(3-4 months).• Produces 300-400 eggs every

2 weeks.• Translucent embryos.• Lots of genome resources available.

Image: TBC

The zebrafish embryo

~3.5 mm

eye heart swim bladder

muscle block

segments

earbrain

notochord

Zebrafish and human disease

• Zebrafish mutants have been produced to model human diseases such as:– Alzheimer's disease– congenital heart disease– polycystic kidney disease– Duchenne muscular dystrophy– malignant melanoma– leukaemia

Forward screening for mutants

P

F2

F3

x

F1

+/+ (50%) +/M (50%)

x

+/+ (25%) +/M (50%) M/M (25%)

+/M +/+

x

ENU-treated male +/+ female

Reverse screening for mutants

Gene of interestGene of interest

Exciting gene expression pattern

Exciting gene expression pattern

Potential human disease gene

Potential human disease gene

Potential new player indevelopmental

pathway

Potential new player indevelopmental

pathwayGene knockoutGene knockout

Phenotype analysisPhenotype analysis

The activity

• Identify differences between the wildtype zebrafish and mutant zebrafish.

• A glossary is provided to help you with scientific terms.

Image: Rodrigo Young, University College London

Flash cards & worksheets

Answers

Image 1

What’s the difference?Embryo B has no eye.

Image: Rodrigo Young, University College London

Image 2

What’s the difference?Fish B is a lighter, golden colour compared to fish A.

Image: Keith C. Cheng, Penn State College of Medicine and Wellcome images

Image 3

What’s the difference?The body of fry B is curved. If you look closely you’ll also see that its mouth is open. This is because it is unable to fully close its mouth as its muscles are too weak.

Image: Elisabeth Busch, Wellcome Trust Sanger Institute and Lehtokari et al 2008, European Journal of Human Genetics

Image 4

What’s the difference?The zebrafish embryos in picture B look paler and are not stained red.

Image: Ana Cvejic, Wellcome Trust Sanger Institute

Image 5

What’s the difference?There are bright green blobs in picture B.

Image: Elisabeth Busch, Wellcome Trust Sanger Institute

Image 6

What’s the difference?Embryo A has more blue dots than embryo B.The blue dots are stained neutrophils moving towards a wound on the zebrafish fin.

Image: Ana Cvejic, Wellcome Trust Sanger Institute