(4)Zebrafish • In its larval stages it is transparent

ZEBRAFISH

as

DEVELOPMENTAL

MODEL

Zebrafish

2

Zebrafish

(Danio rerio)

• About 2.5 cm to 4 cm long

• Males are slender and torpedo- shaped usually with a pink or yellow tinge.

• Females tend to be less pink than the males and are fatter due to the eggs they carry.

Zebrafish

• In its larval stages it is transparent. As it matures to an adult it develops stripes that run along the length of the body and look blue in colour.

• Aided by the transparency of the embryo, if researchers modify the fish's genotype at the egg stage, they can see resulting changes in organ shape or dynamics barely three days later.

Zebra Fish

Life Cycle : Time taken

Zebrafish.mp4.mp4

 Produce 200-300 fertilised eggs every week; an ideal attribute for  genetic studies

 Embryos can be microinjected with mRNA or DNA corresponding  to genes of interest  handing down injected gene to next

       generation

 PRESENT-

 Dimethyl-prostaglandin E2 (dmPGE2) increases the number of  blood stem cells in zebrafish embryos and stem cells in human  cord blood samples

ZEBRAFISH

7

 Large numbers of mutations disrupt embryonic development in  zebrafish, serve as models for human diseases like muscular 

dystrophy, neurodegenrative diseases

 Leflunomide is in early phase clinical trials to kill melanoma cells.

 FUTURE-

 Creation of a transparent version of adult zebrafish. Behaviour of  tumour cells can be followed like the birth, growth and spread of  tumours can be scrutinised

 As a disease model for Tuberculosis because zebrafish embryos  are transparent, infection with fluorescently-labelled 

tuberculosis bacteria.

ZEBRAFISH

8

Zebrafish as a Developmental Model Organism:

Why?

Used for mapping and identifying genes involved in organ development. Excellent model for studying infectious diseases

 Reasons :

1) The zebrafish is small and robust.

2) Cheaper to maintain than mice.

3) Break of daylight triggers mating in zebrafish (many other fish only lay eggs in the dark).

4) Zebrafish produce hundreds of offspring at weekly intervals providing scientists with an ample supply of embryos to study.

5) They grow at an extremely fast rate, developing as much in a day as a human embryo develops in one month.

6) As zebrafish eggs are fertilised and develop outside the mother’s body it is an ideal model organism for studying early development.

7) Zebrafish embryos are nearly transparent which allows researchers to easily examine the development of internal structures.

Every blood vessel in a living zebrafish embryo can be seen using just a low-power microscope.

Zebrafish

8) As a vertebrate, zebrafish has the same major organs and tissues as humans. Their muscle, blood, kidney and eyes share many features with human systems.

9) Zebrafish have the unique ability to repair heart muscle. For example, if part of their heart is removed they can grow it back in a matter of weeks.

Scientists are working to find out the specific factors involved in this process to see if this will help us to develop ways of repairing the heart in humans with heart failure or who have suffered heart attacks.

Zebrafish

Zebrafish Genome

• The zebrafish genome has been fully sequenced to a very high quality. This has enabled scientists to create mutations in more than 14,000 genes to study their function.

For example: Mutations that disrupt embryonic development in zebrafish, serve as models for human diseases like muscular dystrophy, neurodegenrative diseases.

• Zebrafish have 25 chromosomes. Zebrafish genome consists of about 1.5 x 10 billion basepairs. Mammalian genome consists of about 3 x 10 billion basepairs.

• Zebrafish share 70 per cent of genes with humans. 84 per cent of genes known to be associated with human disease have a zebrafish counterpart.

• more than 26,000 protein-coding genes, the largest gene set of any vertebrate so far sequenced

• Comparison to the human reference genome shows

that approximately 70% of human genes have at least

one obvious zebrafish orthologue (Orthologs are

genes in different species that evolved from a

common ancestral gene by speciation. Normally,

orthologs retain the same function in the course of

evolution.)

 Used for mapping and identifying genes involved in organ 

development. Excellent model for studying infectious diseases

 REASONS-

 Has most of the same organs found in mammals. Most human  genes have homologues in zebrafish such as ATP-binding 

domains of kinases

 Zebrafish embryos develop outside the mother’s body and are  transparent throughout the first few days of life.

ZEBRAFISH

14

Zebrafish Genome Found Strikingly Similar to Humans

According to a paper published in Nature, 70 per cent of protein-coding human genes are related to genes found in the zebrafish (Danio rerio), and 84 per cent of

genes known to be associated with human disease have a zebrafish counterpart.