Xenopus frogs are arguably the most versatile vertebrate model organism, especially now that highly efficient gene editing has added genetic approaches to their established strengths of gain of function screens, explant culture, transplants, ease of transgenesis, extracts for biochemistry, regeneration, single embryo transcriptomics and proteomics.
Three major resource centres and two small, specialist ones currently provide resources for researchers using Xenopus. These distribute inbred lines, transgenic and mutant animals to users, but sending all of these as live animals incurs stress to the animals during transport and significant costs for users and funding bodies. To address these challenges, we have worked with the US resource centre (NXR) to develop existing methods for Xenopus sperm freezing to the point where they are robust. We have already successfully sent a few transgenic lines as frozen sperm and now aim to develop this process so it can be used to distribute GA and wild-type gametes worldwide.
We will first optimize the number of aliquots testes can be divided into without compromising fertilization and development of the embryos produced; this will minimize the number of male Xenopus used for research. Experience sending other resources shows that the key to success in this programme is how the sperm are sent, the paperwork that accompanies them to facilitate passage through customs and the instructions with them. We will develop these by an iterative process, first sending dummy packages and then cryopreserved sperm to six test labs around the world, then getting feedback about the timing of arrival, success of embryo production and accuracy of the instructions. We will modify our methods and test again. Once the sperm sending process is robust we will roll it out to other labs progressively, this will allow us to make any necessary changes to the infrastructure and organization at EXRC to support this programme.
Horb M et al. (2019). Xenopus Resources: Transgenic, Inbred and Mutant Animals, Training Opportunities, and Web-Based Support. Frontiers in Physiology 10:387. doi: 10.3389/fphys.2019.00387
Morrow S et al. (2017). Effects of freezing and activation on membrane quality and DNA damage in Xenopus tropicalis and Xenopus laevis spermatozoa. Reproduction, Fertility and Development 29(8):1556-1566. doi: 10.1071/RD16190
Pearl E et al. (2017). An optimized method for cryogenic storage of Xenopus sperm to maximise the effectiveness of research using genetically altered frogs. Theriogenology 92:149-155. doi: 10.1016/j.theriogenology.2017.01.007