Xenopus as an Experimental Organism

Abstract

The South African clawed frog, Xenopus laevis , is a popular model system to study development. It is easy to maintain a breeding frog colony, females can be spawned all year round and hundreds of synchronously growing embryos can be generated from a single fertilisation. Embryos are easily amenable to microsurgery at any stage of development and adults survive surgeries performed under limited aseptic conditions. The ease of injecting oligonucleotides or messenger ribonucleic acid (mRNA) into Xenopus leavis embryos has contributed to the discovery of genes with key functions in development. Another singularity of Xenopus leavis is the ease to manipulate its oocytes before fertilisation; this has been a powerful tool to identify the function of maternally deposited mRNAs in development. Over the past two decades, transgenic strategies have been developed using the related species Xenopus tropicalis and this is broadening the contribution of Xenopus to the understanding of early development. Key Concepts Xenopus laevis is easy to raise and feed in large colonies in the lab, and commercial vendors can now supply frogs and embryos at all developmental stages for research. The female Xenopus can be induced to spawn repeatedly at any season, making it possible to obtain embryos all year round. Xenopus leavis' eggs are large, they measure around 1.3 mm in diameter and are usually laid in large numbers that are fertilised in vitro . The Xenopus embryos develop outside the female, its early development is very fast, making it possible to study a full developmental program in about 3 days, with the possibility to manipulate the embryos at any stage of development. Xenopus leavis oocytes can easily be obtained and manipulated before fertilisation, making it possible to study the function of maternally deposited mRNAs. The mechanisms of tissue and body axis formation have been elucidated from research carried out in Xenopus leavis embryos, and a Xenopus toxicological test called FETAX has been recommended by scientists from the American Food and Drug Administration, for the teratogenic screening of new drugs candidates. Gene editing techniques have been developed for Xenopus, making it an excellent model to mimic human mutations and study human diseases like cancers and congenital diseases. The sequencing of the diploid genome, ease of obtaining and injecting large numbers of eggs and the relatively short lifespan makes Xenopus tropicalis a very powerful model for gene editing and transgenic studies of organogenesis. Eggs of Xenopus leavis provide a model of choice for studying the regulation of the cell cycle. A database called Xenbase is now available to the Xenopus research community; it contains usefully and regularly updated information on Xenopus research and resources.