The European Xenopus Resource Centre

Understanding the cellular and molecular processes that drive tissue and organ function in both the developing embryo and adult organism is critical for improving human and animal health. It underpins intervention in disease and enhances our knowledge of many related processes, including responses to our external environment, e.g., pollution. Animal experiments are essential for this understanding despite advances in cell culture and mathematical modelling. This is particularly so for embryonic development, where many cell types interact in complex ways, and in genetic diseases where multiple organs are affected. A few species have been studied intensively and the collection of experimental tools and information gathered in these "model" organisms means they provide most of our knowledge of animal biology. They include two aquatic Xenopus frogs, and this application is to fund the resource centre for these Xenopus models.

Xenopus females produce hundreds of synchronously developing, extremely robust embryos in a petri dish, allowing microsurgery and very rapid microinjection of proteins, RNA or DNA. The tadpole is largely transparent, allowing the weeklong development of organs to be observed. X. laevis has made critical contributions to our understanding of fundamental cellular function: showing that cells could be reprogrammed to stemness, revealing how cell division is controlled and identifying the molecules responsible for patterning the vertebrate embryo. Genetic experiments switched to X. tropicalis which has a very simple genome. Gene editing efficiency in X. tropicalis allows experiments to be performed without breeding, greatly speeding up experiments and reducing cost. Today Xenopus are excellent choices for both modern and traditional experimental methods.

As genetically altered (GA) lines of Xenopus became common, a resource centre was needed to ensure the quality of these animals, prevent line loss when projects closed, make new lines and to distribute them. The EXRC was set up to do this and, as projects ended, the molecular resources, DNA and antibody collections used for Xenopus work were added. These are unique resources. A second, similar animal holding facility was then set up in the US, allowing all GA lines to be held at both sites, protecting against accidental loss. Having collections in the US and UK limits frog transport, improving welfare. EXRC also promotes welfare by sharing frog resources: females produce excess embryos or oocytes, so these are sent out directly to multiple labs. Male gametes are now sent as chilled testes or frozen sperm, again often shared between labs. These approaches reduce animal use and save lab and funder resources. Scientists and animal technologists come to the EXRC to train or perform specialist techniques and frequently call for advice from EXRC staff who have been in post for up to 16 years, acquiring invaluable knowledge and experience. This application is for continued funding of the EXRC.

To identify current research community needs the EXRC surveyed labs. All acknowledged the value of the EXRC with almost all recognising it as essential for their work and they identified desirable, additional resources. First and most critical was access to wild-type Xenopus, as the main commercial supplier has closed. The centre expanded by 50% this year and can fulfil at least the UK's needs. Another request was for two types of GA line: ones that allow different cell types to be seen fluorescently in X. tropicalis and ones that fluoresce in response to the signals that cells use to communicate. The final request was to provide support for gene editing of Xenopus.

These activities all fit within the footprint, infrastructure and specific expertise of the EXRC, and we are confident that, with BBSRC's financial support supplemented by our ongoing, profit-making work for industry, we shall continue to fulfil the Xenopus community's needs.

Xenopus frogs are powerful model organisms used across a range of disciplines from discovery science in cell and developmental biology, through to the study of human disease in pure and applied genetics and industrial uses such as ecotoxicology. This application is for continued support of the Xenopus resource centre that serves around 200 labs with the majority of its resources being unique. EXRC will continue to make, collect, curate and distribute molecular resources and genetically altered frogs and to provide essential access to high quality wild-type Xenopus for the UK. EXRC will continue to supply Xenopus by-products, for example oocytes, embryos and male gametes. This improves 3Rs by providing products from a single frog to multiple labs and avoiding stressful travel for adult animals. Access to resources is ensured by Xenbase, the model's informatic resource , which details the resources and links to the EXRC's website. Responsiveness to user needs is assured by a strategy board and regular surveys.

To improve services, we have re-built and expanded the animal breeding and holding facilities at the centre. These facilities are populated using "clean" embryos of reduced pathogen load, thus improving biosecurity. A 2022 survey of Xenopus researchers highlighted the importance of the EXRC to all labs, with most citing EXRC as critical or essential. Two new transgenic resources were requested: cell type fluorescent reporter lines in X. tropicalis and cell signalling reporter lines in both frog species. We make transgenic lines regularly and will use the X. laevis cell-type fluorescent constructs to make the X. tropicalis lines and adapt the signalling reporter transgenes from other model animals for both species. Gene editing support was also requested, and we will provide that mainly via the "research hotel" function of the centre.