Why use the frog in research?

Key facts about Xenopus

• Originated in South Africa, today Xenopus are found across the African continent and in some parts of America and Europe.
• Xenopus laevis grow up to about 12 cm in length.
• Xenopus tropicalis grow up to about 5 cm in length.
• X. tropicalis have a much shorter life cycle than X. laevis. X. tropicalis grows into an adult in 4 months, while X. laevis takes 12 months.
• X. laevis have 18 chromosomes and are allotetrapolid (four copies of each chromosome).
• X. tropicalis have 10 chromosomes and are diploid (two copies of each chromosome).
• Xenopus are unusual looking. They have flattened bodies with small heads, no eyelids, muscular hind limbs, fully webbed toes with claws (hence their name) and small front limbs which they use to shovel food into their mouths.
• Xenopus have mottled skin normally greenish, grey in colour on their back with a lighter coloured underside. Other colours are not uncommon though and some are albino.
• Xenopus’ skin gives them camouflage from predators.
• Female Xenopus frogs are about 20 per cent bigger than males.
• Xenopus are fully aquatic.
• Biologically, the Xenopus are the best understood amphibians (Xenbase, Ensembl).

An adult Xenopus laevis.
Image credit: Shutterstock

Benefits of the Xenopus

• Xenopus are easily bred and maintained in the laboratory.
• In captivity, X. laevis can live for as long as 30 years compared to 5-15 years in the wild.
• The frogs themselves are relatively small in size so do not take up too much space in the laboratory.
• Xenopus produce eggs all year round, in the lab. If well fed and cared for, Xenopus females can be induced to mate 4-6 times a year and males once a month.
• Xenopus lay many eggs at once. X. laevis can produce up to 1000 eggs, while X. tropicalis can produce up to 3000.
• Ovulation can be induced all year round with a simple hormone injection.
• The eggs and embryos are relatively large and robust, developing externally in a simple salt solution so that development can be observed at all stages. The eggs are opaque but develop into transparent tadpoles within a couple of days so it is easy to study embryonic development.
• Because the Xenopus embryos develop outside of the body they can easily be surgically manipulated or treated with proteins and chemicals that interfere with development.
• X. tropicalis is a simpler model than X. laevis for genetic studies because it only has two copies of every chromosome compared to X. laevis which has four copies.
• Genetically, Xenopus are very similar to humans and are therefore a good model for human disease.