The amphibian collection includes wild Xenopus species and transgenic lines that are used in fundamental scientific research, particularly for the detection of environmental pollutants. Throughout the world, various amphibians are threatened by climate change and pollution.
The live amphibian collection is used for scientific research, in particular for understanding how a complex process like metamorphosis (that is, how a tadpole becomes a frog) unfolds. The collection comprises two wild species belonging to the Xenopus genre — Xenopus laevis and Xenopus tropicalis, from Southern Africa and tropical Africa respectively — belonging to the Pipidae family. Xenopus are exclusively aquatic species. These animals have been introduced as laboratory animals, and are easy to rear and breed in an aquarium. The collection comprises a large number of adult specimens, however we also rear Xenopus tadpoles.
One of the specific activities of our research unit is generating transgenic Xenopus lines, which are used to find solutions to biological questions, particularly those involving thyroid signalling and disturbance. This signalling, mediated by the Thyroid Hormones, is part of the physiology of all vertebrates. The role of these hormones is essential to ensuring the animal’s normal development but they also act on general metabolic control, ensuring homeostasis throughout the whole body. (For more information on thyroid signalling, see the UMR 7221 website)
The collection is regularly enriched by the generation of new transgenic lines relating to the projects developed in our laboratory, or in collaboration with other research laboratories. It is housed in the “Evolution of endocrinal regulations” laboratory (UMR 7221 MNHN/CNRS).
The Xenopus laevis species was introduced to laboratories in the 1950s. It was used in human pregnancy testing (Hogben test). This species was then commonly used in biology laboratories, as a preferred animal model for the study of early embryonic development.
The Xenopus tropicalis species was introduced more recently to laboratories, due to its smaller size and faster generation time than its close relative Xenopus laevis, but above all for its diploid genome (made up of 10 pairs of chromosomes). Indeed, its entire genome was sequenced in 2010 and has enabled the development of genetic approaches which were more difficult with Xenopus laevis, whose genome is allotetraploid (made up of 18 pairs of chromosomes).
The transgenic animal collection was started in 2001 (Coen et al, PNAS USA 2001). A transgenesis platform has been set up at the laboratory to meet the demands of various internal and collaborative projects. This collection is therefore important for basic research.
The transgenic amphibian collection was put together as part of a number of research programmes. The main purpose of this collection is to have access to reference animals that have applications in fundamental, environmental or applied research, providing study models to answer specific biological questions.
In our laboratory, one of the main areas of research is the study of signalling by Thyroid Hormones in vertebrates. In this respect, the tadpole’s metamorphosis into a frog, a transformation where the underlying mechanism depends exclusively on these thyroid hormones, provides an excellent model for studying these hormonal regulations and their malfunctions. Moreover, the perinatal period in mammals may be compared to the metamorphosis of the amphibians, as both of these periods are characterised by a peak in the thyroid hormones needed for the proper development of the future adult. The X. laevis and X. tropicalis species are therefore non-mammal vertebrate models that are particularly relevant to the study of the molecular mechanisms involved in this signalling.
In terms of environmental research, the XETA (Xenopus Embryo Thyroid signalling Assay) test was developed in the laboratory (Fini et al, Environ. Sci. Technol. 2007) and enables us to target chemical pollutants for their thyroid disturbance potential. This test, for which an international patent has been filed, is at phase 2 of the OECD (Organisation for Economic Co-operation and Development) validation process, and has been the subject of a technology transfer to enable public health issues to be addressed.
Lastly, this collection formed the basis for the creation of the WatchFrog company. As a result of a collaboration between our research team and this company, the Muséum and WatchFrog now share a patent exploitation licence.
Three photos of adult Xenopus, from left to right a female X. tropicalis, a male X. tropicalis and an albino X. laevis.
1. Transgenic tadpole expressing green fluorescent protein under the control of the Myelin Basic Protein promoter (pMBP-GFP) and red fluorescent protein under the control of the neural ß-tubulin promoter (pNßt-RFP) © S. Le Mével - MNHN
2. Transgenic tadpole from line LH1, expressing green fluorescent protein under the control of a promoter inducible by Thyroid Hormones. Left, an untreated tadpole compared with a tadpole treated with Thyroid Hormones, right © S. Le Mével - MNHN
3. Transgenic tadpole expressing green fluorescent protein under the control of the cardiac actin promoter (pCAR-GFP) and red fluorescent protein under the control of the neural ß-tubulin promoter (pNßt-RFP) © S. Le Mével - MNHN
4. Transgenic adult frog expressing green fluorescent protein under the control of a ubiquitous promoter, i.e. expressing itself throughout the animal’s entire body © L. Coen – MNHN