Evaluating recovery potential of the northern white rhinoceros from cryopreserved somatic cells

Genetic load and viability of a future restored northern white rhino population

As biodiversity loss outpaces recovery, conservationists are increasingly turning to novel tools for preventing extinction, including cloning and in vitro gametogenesis of biobanked cells. However, restoration of populations can be hindered by low genetic diversity and deleterious genetic load. The persistence of the northern white rhino (Ceratotherium simum cottoni) now depends on the cryopreserved cells of 12 individuals. These banked genomes have higher genetic diversity than southern white rhinos (C. s. simum), a sister subspecies that successfully recovered from a severe bottleneck, but the potential impact of genetic load is unknown. We estimated how demographic history has shaped genome-wide genetic load in nine northern and 13 southern white rhinos. The bottleneck left southern white rhinos with more fixed and homozygous deleterious alleles and longer runs of homozygosity, whereas northern white rhinos retained more deleterious alleles masked in heterozygosity. To gauge the impact of genetic load on the fitness of a northern white rhino population restored from biobanked cells, we simulated recovery using fitness of southern white rhinos as a benchmark for a viable population. Unlike traditional restoration, cell-derived founders can be reintroduced in subsequent generations to boost lost genetic diversity and relieve inbreeding. In simulations with repeated reintroduction of founders into a restored population, the fitness cost of genetic load remained lower than that borne by southern white rhinos. Without reintroductions, rapid growth of the restored population (>20-30% per generation) would be needed to maintain comparable fitness. Our results suggest that inbreeding depression from genetic load is not necessarily a barrier to recovery of the northern white rhino and demonstrate how restoration from biobanked cells relieves some constraints of conventional restoration from a limited founder pool. Established conservation methods that protect healthy populations will remain paramount, but emerging technologies hold promise to bolster these tools to combat the extinction crisis.

A Method to Freeze Skin Samples for Cryobanks: A Test of Some Cryoprotectants for an Endangered Deer

The genetic diversity of endangered deer species, such as Mazama jucunda, can be preserved with the help of somatic cell cryopreservation. This procedure allows obtaining several cells from the individual even after its death, which is very important for applications in reproductive biotechnologies. This study's objective was to test cryopreservation protocols of skin fragments of M. jucunda, using different cryoprotectants in slow freezing. We evaluated four treatments, composed of three cryoprotectants, dimethyl sulfoxide (DMSO), polyvinylpyrrolidone (PVP), and ethylene glycol (EG), used alone and in combination. There was also a control group where the tissue did not undergo cryopreservation. Skin fragments were collected from the medial region of the pelvic limbs of three individuals. Each fragment was divided into 10 equal parts, standardized by weight, making two pieces for each treatment and control from each animal. The collected fragments were evaluated in culture, based on the speed of occupation of the free spaces of the cell culture flask. Cell viability was also evaluated using Trypan Blue dye and the mitotic index to understand the effect of toxicity and freezing on cell membrane integrity and cell division capacity, respectively. The treatments that used association with PVP proved to be more damaging to the cells, taking longer to reach confluence. EG alone showed better results than DMSO in the slow-freezing protocol. Clinical Trial Registration Number is 1390/21.

In vitro and in vivo development of interspecies Asian elephant embryos reconstructed with pig enucleated oocytes

Interspecies somatic cell nuclear transfer (iSCNT) has an immense potential to rescue endangered animals and extinct species like mammoths. In this study, we successfully established an Asian elephant's fibroblast cell lines from ear tissues, performed iSCNT with porcine oocytes and evaluated the in vitro and in vivo development of reconstructed embryos. A total of 7780 elephant-pig iSCNT embryos were successfully reconstructed and showed in vitro development with cleavage rate, 4-cell, 8-cell and blastocyst rate of 73.01, 30.48, 5.64, and 4.73%, respectively. The total number of elephant-pig blastocyte cells and diameter of hatched blastocyte was 38.67 and 252.75 μm, respectively. Next, we designed species-specific markers targeting EDNRB, AGRP and TYR genes to verify the genome of reconstructed embryos with donor nucleus/species. The results indicated that 53.2, 60.8, and 60.8% of reconstructed embryos (n = 235) contained elephant genome at 1-cell, 2-cell and 4-cell stages, respectively. However, the percentages decreased to 32.3 and 32.7% at 8-cell and blastocyst stages, respectively. Furthermore, we also evaluated the in vivo development of elephant-pig iSCNT cloned embryos and transferred 2260 reconstructed embryos into two surrogate gilts that successfully became pregnant and a total of 11 (1 and 10) fetuses were surgically recovered after 17 and 19 days of gestation, respectively. The crown-rump length and width of elephant-pig cloned fetuses were smaller than the control group. Unfortunately, none of these fetuses contained elephant genomes, which suggested that elephant embryos failed to develop in vivo. In conclusion, we successfully obtained elephant-pig reconstructed embryos for the first time and these embryos are able to develop to blastocyst, but the in vivo developmental failure needs further investigated.

Maximizing the potential for living cell banks to contribute to global conservation priorities

Although cryobanking represents a powerful conservation tool, a lack of standardized information on the species represented in global cryobanks, and inconsistent prioritization of species for future sampling, hinder the conservation potential of cryobanking, resulting in missed conservation opportunities. We analyze the representation of amphibian, bird, mammal, and reptile species within the San Diego Zoo Wildlife Alliance Frozen Zoo® living cell collection (as of April 2019) and implement a qualitative framework for the prioritization of species for future sampling. We use global conservation assessment schemes (including the International Union for Conservation of Nature (IUCN) Red List of Threatened Species™, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), the Alliance for Zero Extinction, the EDGE of Existence, and Climate Change Vulnerability), and opportunities for sample acquisition from the global zoo and aquarium community, to identify priority species for cryobanking. We show that 965 species, including 5% of all IUCN Red List "Threatened" amphibians, birds, mammals, and reptiles, were represented in the collection and that sampling from within existing zoo and aquarium collections could increase representation to 16.6% (by sampling an additional 707 "Threatened" species). High-priority species for future cryobanking efforts include the whooping crane (Grus americana), crested ibis (Nipponia nippon), and Siberian crane (Leucogeranus leucogeranus). Each of these species are listed under every conservation assessment scheme and have ex situ populations available for sampling. We also provide species prioritizations based on subsets of these assessment schemes together with sampling opportunities from the global zoo and aquarium community. We highlight the difficulties in obtaining in situ samples, and encourage the formation of a global cryobanking database together with the establishment of new cryobanks in biodiversity-rich regions.

Understanding Local Adaptation to Prepare Populations for Climate Change

Adaptation within species to local environments is widespread in nature. Better understanding this local adaptation is critical to conserving biodiversity. However, conservation practices can rely on species’ trait averages or can broadly assume homogeneity across the range to inform management. Recent methodological advances for studying local adaptation provide the opportunity to fine-tune efforts for managing and conserving species. The implementation of these advances will allow us to better identify populations at greatest risk of decline because of climate change, as well as highlighting possible strategies for improving the likelihood of population persistence amid climate change. In the present article, we review recent advances in the study of local adaptation and highlight ways these tools can be applied in conservation efforts. Cutting-edge tools are available to help better identify and characterize local adaptation. Indeed, increased incorporation of local adaptation in management decisions may help meet the imminent demands of managing species amid a rapidly changing world.

Knockdown of YY1 Inhibits XIST Expression and Enhances Cloned Pig Embryo Development

The technique of cloning has wide applications in animal husbandry and human biomedicine. However, the very low developmental efficiency of cloned embryos limits the application of cloning. Ectopic XIST-expression-induced abnormal X chromosome inactivation (XCI) is a primary cause of the low developmental competence of cloned mouse and pig embryos. Knockout or knockdown of XIST improves cloning efficiency in both pigs and mice. The transcription factor Yin yang 1(YY1) plays a critical role in XCI by triggering the transcription of X-inactive specific transcript (XIST) and facilitating the localization of XIST RNA on the X chromosome. This study aimed to investigate whether RNA interference to suppress the expression of YY1 can inhibit erroneous XIST expression, rescue abnormal XCI, and improve the developmental ability of cloned pig embryos. The results showed that YY1 binds to the 5' regulatory region of the porcine XIST gene in pig cells. The microinjection of YY1 siRNA into cloned pig embryos reduced the transcript abundance of XIST and upregulated the mRNA level of X-linked genes at the 4-cell and blastocyst stages. The siRNA-mediated knockdown of YY1 altered the transcriptome and enhanced the in vitro and in vivo developmental efficiency of cloned porcine embryos. These results suggested that YY1 participates in regulating XIST expression and XCI in cloned pig embryos and that the suppression of YY1 expression can increase the developmental rate of cloned pig embryos. The present study established a new method for improving the efficiency of pig cloning.

Resetting the paradigm of reproductive science and conservation

In the application of reproductive science to conservation breeding, it has long been assumed that artificial insemination using frozen thawed sperm would be the default technology. This has always been problematic considering the wide range of tolerance to freeze thawing among vertebrate sperm. Furthermore, those providing leadership for genome banking should be proactive to preserve maximum genetic diversity, however, for many species there is little or no sperm motility after thawing of cryopreserved sperm. In this review article, there is the contention that a much wider range of tissues should be banked, and the range of evolving advanced reproductive and developmental technologies should be considered for conservation breeding programs, to realize the maximum opportunities of genome banking to contribute to conservation of animal species.

Whole-genome resequencing of Chinese pangolins reveals a population structure and provides insights into their conservation

Poaching and trafficking have a substantial negative impact on the population growth and range expansion of the Chinese pangolin (Manis pentadactyla). However, recently reported activities of Chinese pangolins in several sites of Guangdong province in China indicate a promising sign for the recovery of this threatened species. Here, we re-sequence genomes of 15 individuals and perform comprehensive population genomics analyses with previously published 22 individuals. These Chinese pangolins are found to be divided into three distinct populations. Multiple lines of evidence indicate the existence of a newly discovered population (CPA) comprises entirely of individuals from Guangdong province. The other two populations (CPB and CPC) have previously been documented. The genetic differentiation of the CPA and CPC is extremely large (F_ST = 0.541), which is larger than many subspecies-level differentiations. Even for the closer CPA and CPB, their differentiation (F_ST = 0.101) is still comparable with the population-level differentiation of many endangered species. Further analysis reveals that the CPA and CPB populations separate 2.5–4.0 thousand years ago (kya), and on the other hand, CPA and CPC diverge around 25–40 kya. The CPA population harbors more runs of homozygosity (ROHs) than the CPB and CPC populations, indicating that inbreeding is more prevalent in the CPA population. Although the CPC population has less mutational load than CPA and CPB populations, we predict that several Loss of Function (LoF) mutations will be translocated into the CPA or CPB populations by using the CPC as a donor population for genetic rescue. Our findings imply that the conservation of Chinese pangolins is challenging, and implementing genetic rescue among the three groups should be done with extreme caution.

Whole-genome resequencing of Chinese pangolins reveals a new population CPA that is genetically distinct from and harbor more homozygosity than CPB and CPC populations, indicating prevalence in inbreeding and implying challenges in conservation.

Naïve-like pluripotency to pave the way for saving the northern white rhinoceros from extinction

The northern white rhinoceros (NWR) is probably the earth’s most endangered mammal. To rescue the functionally extinct species, we aim to employ induced pluripotent stem cells (iPSCs) to generate gametes and subsequently embryos in vitro. To elucidate the regulation of pluripotency and differentiation of NWR PSCs, we generated iPSCs from a deceased NWR female using episomal reprogramming, and observed surprising similarities to human PSCs. NWR iPSCs exhibit a broad differentiation potency into the three germ layers and trophoblast, and acquire a naïve-like state of pluripotency, which is pivotal to differentiate PSCs into primordial germ cells (PGCs). Naïve culturing conditions induced a similar expression profile of pluripotency related genes in NWR iPSCs and human ESCs. Furthermore, naïve-like NWR iPSCs displayed increased expression of naïve and PGC marker genes, and a higher integration propensity into developing mouse embryos. As the conversion process was aided by ectopic BCL2 expression, and we observed integration of reprogramming factors, the NWR iPSCs presented here are unsuitable for gamete production. However, the gained insights into the developmental potential of both primed and naïve-like NWR iPSCs are fundamental for in future PGC-specification in order to rescue the species from extinction using cryopreserved somatic cells.

Ex Situ Conservation and Genetic Rescue of Endangered Polish Cattle and Pig Breeds with the Aid of Modern Reproductive Biotechnology – A Review

The development and optimization of reproductive biotechnology – specifically semen cryopreservation, spermatological diagnostics, and intraspecies cloning by somatic cell nuclear transfer (SCNT) – have become essential techniques to conserve the genetic resources and establish genetic reserves of endangered or vanishing native Polish livestock breeds. Moreover, this biotechnology is necessary for perpetuating biological diversity and enhancing genetic variability as well as for restoring and reintroducing breeds into anthropogenic agricultural ecosystems. On the one hand, the purpose of our paper is to interpret recent efforts aimed at the ex situ conservation of native cattle and pig breeds. On the other, it emphasizes the prominent role played by the National Research Institute of Animal Production (NRIAP) in maintaining biodiversity in agricultural environmental niches. Furthermore, our paper provides an overview of the conventional and modern strategies of the banking and cryopreservation of germplasm-carrier biological materials and somatic cell lines, spermatological diagnostics, and semen-based and SCNT-mediated assisted reproductive technologies (ART s). These are the most reliable and powerful tools for ex situ protection of the genetic resources of endangered breeds of livestock, especially cattle and pigs.

Ancient and modern genomes unravel the evolutionary history of the rhinoceros family

Only five species of the once-diverse Rhinocerotidae remain, making the reconstruction of their evolutionary history a challenge to biologists since Darwin. We sequenced genomes from five rhinoceros species (three extinct and two living), which we compared to existing data from the remaining three living species and a range of outgroups. We identify an early divergence between extant African and Eurasian lineages, resolving a key debate regarding the phylogeny of extant rhinoceroses. This early Miocene (∼16 million years ago [mya]) split post-dates the land bridge formation between the Afro-Arabian and Eurasian landmasses. Our analyses also show that while rhinoceros genomes in general exhibit low levels of genome-wide diversity, heterozygosity is lowest and inbreeding is highest in the modern species. These results suggest that while low genetic diversity is a long-term feature of the family, it has been particularly exacerbated recently, likely reflecting recent anthropogenic-driven population declines.

Historical population declines prompted significant genomic erosion in the northern and southern white rhinoceros (Ceratotherium simum)

Large vertebrates are extremely sensitive to anthropogenic pressure, and their populations are declining fast. The white rhinoceros (Ceratotherium simum) is a paradigmatic case: this African megaherbivore has suffered a remarkable decline in the last 150 years due to human activities. Its subspecies, the northern (NWR) and the southern white rhinoceros (SWR), however, underwent opposite fates: the NWR vanished quickly, while the SWR recovered after the severe decline. Such demographic events are predicted to have an erosive effect at the genomic level, linked to the extirpation of diversity, and increased genetic drift and inbreeding. However, there is little empirical data available to directly reconstruct the subtleties of such processes in light of distinct demographic histories. Therefore, we generated a whole-genome, temporal data set consisting of 52 resequenced white rhinoceros genomes, representing both subspecies at two time windows: before and during/after the bottleneck. Our data reveal previously unknown population structure within both subspecies, as well as quantifiable genomic erosion. Genome-wide heterozygosity decreased significantly by 10% in the NWR and 36% in the SWR, and inbreeding coefficients rose significantly by 11% and 39%, respectively. Despite the remarkable loss of genomic diversity and recent inbreeding it suffered, the only surviving subspecies, the SWR, does not show a significant accumulation of genetic load compared to its historical counterpart. Our data provide empirical support for predictions about the genomic consequences of shrinking populations, and our findings have the potential to inform the conservation efforts of the remaining white rhinoceroses.

Genomic insights into the conservation status of the world's last remaining Sumatran rhinoceros populations

Small populations are often exposed to high inbreeding and mutational load that can increase the risk of extinction. The Sumatran rhinoceros was widespread in Southeast Asia, but is now restricted to small and isolated populations on Sumatra and Borneo, and most likely extinct on the Malay Peninsula. Here, we analyse 5 historical and 16 modern genomes from these populations to investigate the genomic consequences of the recent decline, such as increased inbreeding and mutational load. We find that the Malay Peninsula population experienced increased inbreeding shortly before extirpation, which possibly was accompanied by purging. The populations on Sumatra and Borneo instead show low inbreeding, but high mutational load. The currently small population sizes may thus in the near future lead to inbreeding depression. Moreover, we find little evidence for differences in local adaptation among populations, suggesting that future inbreeding depression could potentially be mitigated by assisted gene flow among populations.

The ART of bringing extinction to a freeze - History and future of species conservation, exemplified by rhinos

The ongoing mass extinction of animal species at an unprecedented rate is largely caused by human activities. Progressive habitat destruction and fragmentation is resulting in accelerated loss of biodiversity on a global scale. Over decades, captive breeding programs of non-domestic species were characterized by efforts to optimize species-specific husbandry, to increase studbook-based animal exchange, and to improve enclosure designs. To counter the ongoing dramatic loss of biodiversity, new approaches are warranted. Recently, new ideas, particularly the application of assisted reproduction technologies (ART), have been incorporated into classical zoo breeding programs. These technologies include semen and oocyte collection, artificial insemination, and in-vitro embryo generation. More futuristic ideas of advanced ART (aART) implement recent advances in biotechnology and stem-cell related approaches such as cloning, inner cell mass transfer (ICM), and the stem-cell-associated techniques (SCAT) for the generation of gametes and ultimately embryos of highly endangered species, such as the northern white rhinoceros (Ceratotherium simum cottoni) of which only two female individuals are left. Both, ART and aART greatly depend on and benefit from the rapidly evolving cryopreservation techniques and biobanking not only of genetic, but also of viable cellular materials suitable for the generation of induced pluripotent stem cells (iPSC). The availability of cryopreserved materials bridges gaps in time and space, thereby optimizing the available genetic variability and enhancing the chance to restore viable populations.

Interspecific Gene Flow and the Evolution of Specialization in Black and White Rhinoceros

Africa's black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros are closely related sister-taxa that evolved highly divergent obligate browsing and grazing feeding strategies. Although their precursor species Diceros praecox and Ceratotherium mauritanicum appear in the fossil record ∼5.2 Ma, by 4 Ma both were still mixed feeders, and were even spatiotemporally sympatric at several Pliocene sites in what is today Africa's Rift Valley. Here, we ask whether or not D. praecox and C. mauritanicum were reproductively isolated when they came into Pliocene secondary contact. We sequenced and de novo assembled the first annotated black rhinoceros reference genome and compared it with available genomes of other black and white rhinoceros. We show that ancestral gene flow between D. praecox and C. mauritanicum ceased sometime between 3.3 and 4.1 Ma, despite conventional methods for the detection of gene flow from whole genome data returning false positive signatures of recent interspecific migration due to incomplete lineage sorting. We propose that ongoing Pliocene genetic exchange, for up to 2 My after initial divergence, could have potentially hindered the development of obligate feeding strategies until both species were fully reproductively isolated, but that the more severe and shifting paleoclimate of the early Pleistocene was likely the ultimate driver of ecological specialization in African rhinoceros.

Rewinding Extinction in the Northern White Rhinoceros: Genetically Diverse Induced Pluripotent Stem Cell Bank for Genetic Rescue

Extinction rates are rising, and current conservation technologies may not be adequate for reducing species losses. Future conservation efforts may be aided by the generation of induced pluripotent stem cells (iPSCs) from highly endangered species. Generation of a set of iPSCs from multiple members of a species can capture some of the dwindling genetic diversity of a disappearing species. We generated iPSCs from fibroblasts cryopreserved in the Frozen Zoo^®: nine genetically diverse individuals of the functionally extinct northern white rhinoceros (Ceratotherium simum cottoni) and two from the closely related southern white rhinoceros (Ceratotherium simum simum). We used a nonintegrating Sendai virus reprogramming method and developed analyses to confirm the cells' pluripotency and differentiation potential. This work is the first step of a long-term interdisciplinary plan to apply assisted reproduction techniques to the conservation of this highly endangered species. Advances in iPSC differentiation may enable generation of gametes in vitro from deceased and nonreproductive individuals that could be used to repopulate the species.

Reference genome and demographic history of the most endangered marine mammal, the vaquita

The vaquita is the most critically endangered marine mammal, with fewer than 19 remaining in the wild. First described in 1958, the vaquita has been in rapid decline for more than 20 years resulting from inadvertent deaths due to the increasing use of large-mesh gillnets. To understand the evolutionary and demographic history of the vaquita, we used combined long-read sequencing and long-range scaffolding methods with long- and short-read RNA sequencing to generate a near error-free annotated reference genome assembly from cell lines derived from a female individual. The genome assembly consists of 99.92% of the assembled sequence contained in 21 nearly gapless chromosome-length autosome scaffolds and the X-chromosome scaffold, with a scaffold N50 of 115 Mb. Genome-wide heterozygosity is the lowest (0.01%) of any mammalian species analysed to date, but heterozygosity is evenly distributed across the chromosomes, consistent with long-term small population size at genetic equilibrium, rather than low diversity resulting from a recent population bottleneck or inbreeding. Historical demography of the vaquita indicates long-term population stability at less than 5,000 (Ne) for over 200,000 years. Together, these analyses indicate that the vaquita genome has had ample opportunity to purge highly deleterious alleles and potentially maintain diversity necessary for population health.

Pre-extinction Demographic Stability and Genomic Signatures of Adaptation in the Woolly Rhinoceros

Ancient DNA has significantly improved our understanding of the evolution and population history of extinct megafauna. However, few studies have used complete ancient genomes to examine species responses to climate change prior to extinction. The woolly rhinoceros (Coelodonta antiquitatis) was a cold-adapted megaherbivore widely distributed across northern Eurasia during the Late Pleistocene and became extinct approximately 14 thousand years before present (ka BP). While humans and climate change have been proposed as potential causes of extinction [1-3], knowledge is limited on how the woolly rhinoceros was impacted by human arrival and climatic fluctuations [2]. Here, we use one complete nuclear genome and 14 mitogenomes to investigate the demographic history of woolly rhinoceros leading up to its extinction. Unlike other northern megafauna, the effective population size of woolly rhinoceros likely increased at 29.7 ka BP and subsequently remained stable until close to the species' extinction. Analysis of the nuclear genome from a ∼18.5-ka-old specimen did not indicate any increased inbreeding or reduced genetic diversity, suggesting that the population size remained steady for more than 13 ka following the arrival of humans [4]. The population contraction leading to extinction of the woolly rhinoceros may have thus been sudden and mostly driven by rapid warming in the Bølling-Allerød interstadial. Furthermore, we identify woolly rhinoceros-specific adaptations to arctic climate, similar to those of the woolly mammoth. This study highlights how species respond differently to climatic fluctuations and further illustrates the potential of palaeogenomics to study the evolutionary history of extinct species.

What animals can teach us about evolution, the human genome, and human disease

During the past 20 years, since I started as a postdoc, the world of genetics and genomics has changed dramatically. My main research goal throughout my career has been to understand human disease genetics, and I have developed comparative genomics and comparative genetics to generate resources and tools for understanding human disease. Through comparative genomics I have worked to sequence enough mammals to understand the functional potential of each base in the human genome as well as chosen vertebrates to study the evolutionary changes that have given many species their key traits. Through comparative genetics, I have developed the dog as a model for human disease, characterising the genome itself and determining a list of germ-line loci and somatic mutations causing complex diseases and cancer in the dog. Pulling all these findings and resources together opens new doors for understanding genome evolution, the genetics of complex traits and cancer in man and his best friend.

De-Extinction

De-extinction projects for species such as the woolly mammoth and passenger pigeon have greatly stimulated public and scientific interest, producing a large body of literature and much debate. To date, there has been little consistency in descriptions of de-extinction technologies and purposes. In 2016, a special committee of the International Union for the Conservation of Nature (IUCN) published a set of guidelines for de-extinction practice, establishing the first detailed description of de-extinction; yet incoherencies in published literature persist. There are even several problems with the IUCN definition. Here I present a comprehensive definition of de-extinction practice and rationale that expounds and reconciles the biological and ecological inconsistencies in the IUCN definition. This new definition brings together the practices of reintroduction and ecological replacement with de-extinction efforts that employ breeding strategies to recover unique extinct phenotypes into a single “de-extinction” discipline. An accurate understanding of de-extinction and biotechnology segregates the restoration of certain species into a new classification of endangerment, removing them from the purview of de-extinction and into the arena of species’ recovery. I term these species as “evolutionarily torpid species”; a term to apply to species falsely considered extinct, which in fact persist in the form of cryopreserved tissues and cultured cells. For the first time in published literature, all currently active de-extinction breeding programs are reviewed and their progress presented. Lastly, I review and scrutinize various topics pertaining to de-extinction in light of the growing body of peer-reviewed literature published since de-extinction breeding programs gained public attention in 2013.