Developing a nuclear transplantation model for Australian amphibian conservation using a common species of Australian Frog (Limnodynastes peronii)

Abstract

As amphibian populations continue to decline, there is a need to establish procedures to store and recover genetic diversity. Nuclear transplantation (NT) is a potentially useful reproductive technology with applications to conservation in specific circumstances. Although sperm have been successfully cryopreserved and used in in vitro fertilization to produce sexually mature offspring, there are many endangered and even extinct amphibian species that only exist as stored frozen adult or larval tissues. The only way to recover that genetic diversity is through NT. Nuclear transplantation can introduce new genes into captive breeding programs from individuals where no viable gametes from that individual have been cryopreserved. Amphibian NT research was common during the middle to late 20th century; however, it was never conducted for amphibian conservation. Early amphibian NT experiments were conducted for the purpose of determining whether differentiation was a terminal process that involved the loss of reprogramming genes. However, following the success of mammalian NT, amphibian NT research declined, and the field has been at a standstill for decades. This study developed the first nuclear transplantation protocol for a native Australia frog using Limnodynastes peronii, as a model. Specifically, this paper aimed to test: 1) nuclear transplantation with fresh embryonic cells in Limnodynastes peronii and trial the implementation of different egg enucleation methods (pricked eggs only, UV only, and pricked + UV), 2) use of cryopreserved cells in nuclear transplantation and 3) use single nucleotide polymorphisms to determine if the nuclear genomes of nuclear transplant embryos were derived from the injected donor cell nuclei. With both fresh and cryopreserved embryonic cells as donor cell nuclei, development of the nuclear transplant embryos was low compared to the fertilized controls. Only one nuclear transplant embryo derived from a fresh embryonic cell (injected into a UV only enucleated egg) developed into a tadpole. This attained stage 36 of the Gosner Staging System for Anurans (hind limbs) before dying. As an egg activation technique, pricking the eggs resulted in higher cleavage rates and development to blastula than UV only and pricked + UV nuclear transplants (in trials with cryopreserved cells), but none of the nuclear transplants from the pricked only group developed beyond blastula. None of the nuclear transplants derived from cryopreserved embryonic cells developed to tadpoles. The most advanced stage attained from cryopreserved embryonic cells was stage 13 (neurula) from UV only eggs. Single nucleotide polymorphism (SNP) analysis testing for genotype mismatches was used to determine if the genomes of developing nuclear transplant embryos were derived from the injected donor cell nucleus. SNP analysis confirmed that two true clones were generated in this study. This is the first confirmed nuclear transplantation in any Australian native frog.