Danio rerio (Zebrafish)

The Zebrafish is a widely used vertebrate model for development, it was first established as a useful model organism by George Streisinger, Zebrafish are as commonly used as rats and mice. Studies involving Zebrafish have been important in many fields of research including oncology, regeneration and particularly embryonic development.

Zebrafish develop in a very similar way to most higher vertebrates, including humans, with one key difference; the embryo develops outside of the Zebrafish in a see-through egg. In addition to this the embryo itself is transparent, allowing researchers to easily monitor development of the embryo as a whole and its internal features. Zebrafish have 25 chromosomes and about half the number of base pairs of humans.

There are many online resources with information on Zebrafish, the main source of information for scientists worldwide is the ZFIN. The ZFIN is the Zebrafish Information Network, it is an online database which provides information for researchers.

Advantages of the Zebrafish as a model organism:

• Very quick rate of development, with a lot happening in the first 24 hours.
• Fully sequenced Genome, and there is a wide variety of known mutants.
• Transparent embryo makes it easy to monitor development.
• It is a robust animal which can survive in a variety of conditions.
• Fate maps have been created of the Zebrafish at several stages of development.
• Can lay in excess of 100 eggs per week.

Disadvantages of the Zebrafish as a model organism: 

• Need to live in an aquatic environment which can be expensive.
• Although they are good vertebrate models they are not as closely related to humans as mice.
• Cannot yet create specific gene KO's, all mutations are just random.

Techniques used with Zebrafish:

• Reverse genetics: Identifying the phenotype of a specific gene sequence. This technique helped researchers to identify p53 mutants which have a predisposition to cancer and rag1 deficient Zebrafish suffered with immunodeficiency.
• Transgenesis: The introduction of a 'transgene' into an organism so that it will demonstrate the properties of that gene in its new host. This technique has provided researchers with the opportunity to observe development in vivo and in real time. It can be used in conjunction with GFP to highlight specific proteins or molecules.
• Chemical genetics: Directly modifies protein function via the introduction of small molecules. This technique has been very successful in Zebrafish and has lead to the identification of a chemical that suppresses a specific cardiovascular disease.

Zebrafish in medical research:

The Zebrafish has played key roles in research into developmental heart defects and cancer. The use of Zebrafish lead to the discovery of the mutant Cardiofunk (Cfk) which lead to defects in heart valves due to a mutation in an actin gene which prevented muscle tissue in the heart from forming properly. 

References:

https://www.zf-models.org/information/factsheet.html

https://zfin.org/cgi-bin/webdriver?MIval=aa-ZDB_home.apg

Principles of Development 3rd edition - Lewis Wolpert

Image courtesy of Wikimedia Commons.