Potential role of intraspecific and interspecific cloning in the conservation of wild mammals

Biobanks, offspring fitness and the influence of developmental plasticity in conservation biology

Mitigation of the widely known threats to the world's biodiversity is difficult, despite the strategies and actions proposed by international agreements such as the United Nations Framework Convention on Climate Change (UNFCCC) and the Convention on Biological Diversity (CBD). Nevertheless, many scientists devote their time and effort to finding and implementing various solutions to the problem. One potential way forward that is gaining popularity involves the establishment of biobank programs aimed at preserving and storing germplasm from threatened species, and then using it to support the future viability and health of threatened populations. This involves developing and using assisted reproductive technologies to achieve their goals. Despite considerable advances in the effectiveness of reproductive technologies, differences between the reproductive behavior and physiology of widely differing taxonomic groups mean that this approach cannot be applied with equal success to many species. Moreover, evidence that epigenetic influences and developmental plasticity, whereby it is now understood that embryonic development, and subsequent health in later life, can be affected by peri-conceptional environmental conditions, is raising the possibility that cryopreservation methods themselves may have to be reviewed and revised when planning the biobanks. Here, I describe the benefits and problems associated with germplasm biobanking across various species, but also offer some realistic assessments of current progress and applications.

Derivation of embryonic stem cells from wild-derived mouse strains by nuclear transfer using peripheral blood cells

Wild-derived mouse strains have been extensively used in biomedical research because of the high level of inter-strain polymorphisms and phenotypic variations. However, they often show poor reproductive performance and are difficult to maintain by conventional in vitro fertilization and embryo transfer. In this study, we examined the technical feasibility of derivation of nuclear transfer embryonic stem cells (ntESCs) from wild-derived mouse strains for their safe genetic preservation. We used leukocytes collected from peripheral blood as nuclear donors without sacrificing them. We successfully established 24 ntESC lines from two wild-derived strains of CAST/Ei and CASP/1Nga (11 and 13 lines, respectively), both belonging to Mus musculus castaneus, a subspecies of laboratory mouse. Most (23/24) of these lines had normal karyotype, and all lines examined showed teratoma formation ability (4 lines) and pluripotent marker gene expression (8 lines). Two male lines examined (one from each strain) were proven to be competent to produce chimeric mice following injection into host embryos. By natural mating of these chimeric mice, the CAST/Ei male line was confirmed to have germline transmission ability. Our results demonstrate that inter-subspecific ntESCs derived from peripheral leukocytes could provide an alternative strategy for preserving invaluable genetic resources of wild-derived mouse strains.

Full confluency, serum starvation, and roscovitine for inducing arrest in the G0/G1 phase of the cell cycle in puma skin-derived fibroblast lines

The puma population is constantly decreasing, and cloning by somatic cell nuclear transfer can be used to conserve the species. One of the factors determining the success of the development of cloned embryos is the cell cycle stage of the donor cells. We evaluated the effects of full confluency (~100%), serum starvation (0.5% serum), and roscovitine (15 µM) treatments on the cell cycle synchronization in G₀/G₁ of puma skin-derived fibroblasts by flow cytometric analysis. Also, we assessed the effects of these synchronization methods on morphology, viability, and apoptosis levels using microscopy tools. The results showed that culturing the cells to confluence for 24 h (84.0%), 48 h (84.6%), and 72 h (84.2%) and serum starvation for 96 h (85.4%) yielded a significantly higher percentage of cells arrested in the G₀/G₁ (P 0.05) phase than cells not subjected to any cell cycle synchronization method (73.9%). Nevertheless, while serum starvation reduced the percentage of viable cells, no difference was observed for the full confluence and roscovitine treatments (P 0.05). Moreover, roscovitine for 12 h (78.6%) and 24 h (82.1%) was unable to synchronize cells in G₀/G₁ (P 0.05). In summary, full confluency induces puma fibroblast cell cycle synchronization at the G₀/G₁ stage without affecting cell viability. These outcomes may be valuable for planning donor cells for somatic cell nuclear transfer in pumas.

Resurrecting biodiversity: advanced assisted reproductive technologies and biobanking

Biodiversity is defined as the presence of a variety of living organisms on the Earth that is essential for human survival. However, anthropogenic activities are causing the sixth mass extinction, threatening even our own species. For many animals, dwindling numbers are becoming fragmented populations with low genetic diversity, threatening long-term species viability. With extinction rates 1000–10,000 times greater than natural, ex situ and in situ conservation programmes need additional support to save species. The indefinite storage of cryopreserved (−196°C) viable cells and tissues (cryobanking), followed by assisted or advanced assisted reproductive technology (ART: utilisation of oocytes and spermatozoa to generate offspring; aART: utilisation of somatic cell genetic material to generate offspring), may be the only hope for species’ long-term survival. As such, cryobanking should be considered a necessity for all future conservation strategies. Following cryopreservation, ART/aART can be used to reinstate lost genetics back into a population, resurrecting biodiversity. However, for this to be successful, species-specific protocol optimisation and increased knowledge of basic biology for many taxa are required. Current ART/aART is primarily focused on mammalian taxa; however, this needs to be extended to all, including to some of the most endangered species: amphibians. Gamete, reproductive tissue and somatic cell cryobanking can fill the gap between losing genetic diversity today and future technological developments. This review explores species prioritisation for cryobanking and the successes and challenges of cryopreservation and multiple ARTs/aARTs. We here discuss the value of cryobanking before more species are lost and the potential of advanced reproductive technologies not only to halt but also to reverse biodiversity loss.

New developments in the field of genomic technologies and their relevance to conservation management

Recent technological advances in the field of genomics offer conservation managers and practitioners new tools to explore for conservation applications. Many of these tools are well developed and used by other life science fields, while others are still in development. Considering these technological possibilities, choosing the right tool(s) from the toolbox is crucial and can pose a challenging task. With this in mind, we strive to inspire, inform and illuminate managers and practitioners on how conservation efforts can benefit from the current genomic and biotechnological revolution. With inspirational case studies we show how new technologies can help resolve some of the main conservation challenges, while also informing how implementable the different technologies are. We here focus specifically on small population management, highlight the potential for genetic rescue, and discuss the opportunities in the field of gene editing to help with adaptation to changing environments. In addition, we delineate potential applications of gene drives for controlling invasive species. We illuminate that the genomic toolbox offers added benefit to conservation efforts, but also comes with limitations for the use of these novel emerging techniques.

Effects of Incubation Time and Method of Cell Cycle Synchronization on Collared Peccary Skin-Derived Fibroblast Cell Lines

The success of cloning by somatic cell nuclear transfer depends on the efficiency of nuclear reprogramming, with the cycle stage of the donor cell playing a crucial role. Therefore, the aim was to evaluate three different approaches for cell cycle synchronization: (i) serum starvation (SS) for 1 to 4 days, (ii) contact inhibition (CI) for 1 to 3 days, and (iii) using cell cycle regulatory inhibitors (dimethyl sulfoxide, cycloheximide, cytochalasin B, or 6-dimethylaminopurine) for 1 and 2 days, in terms of their effects on synchronization in G0/G1 phases and viability of collared peccary skin fibroblasts. Flow cytometry analysis revealed that SS for 4 days (79.0% ± 1.6) and CI for 3 days (78.0% ± 1.4) increased the percentage of fibroblasts in G0/G1 compared to growing cells GC (68.1% ± 8.6). However, SS for 3 and 4 days reduced the viability evaluated by differential staining (81.4% ± 0.03 and 81.6% ± 0.06) compared to growing cells (GC, 95.9% ± 0.06). CI did not affect the viability at any of the analyzed time intervals. No cell cycle inhibitors promoted synchronization in G0/G1. These results indicate that CI for 3 days was the most efficient method for cell cycle synchronization in peccary fibroblasts.

Investigating Markers of Reprogramming Potential in Somatic Cell Lines Derived from Matched Donors

Somatic cell biobanking and related technologies, somatic cell nuclear transfer (SCNT), and induction of pluripotent stem cells offer significant promise for wildlife conservation, but have yet to achieve optimal success. Inefficiency and variability in outcome have been linked to incomplete nuclear reprogramming, highlighting the importance of donor cell contribution. Studies show significant differences in SCNT outcome in donor cell lines within and between individuals, highlighting the necessity for a standardized characterization method to evaluate cell line reprogramming potential. Stringently standardized bovine fibroblast cell lines were generated and assessed for inter- and intraindividual variability on cellular (morphology, chromosome number, apoptotic incidence; Experiment 1) and molecular (pluripotency and epigenetic-related gene expression; Experiment 2) levels encompassing putative biomarkers of reprogramming potential. Cellular parameters were similar across cell lines. While some statistically significant differences were observed in DNMT1, DNMT3B, and HAT1, but not HDAC1, their biological relevance could not be determined with the information at hand. This study lays the foundation for understanding cellular characteristics in cultured cell lines; however, further studies are required to determine any correlation with reprogramming potential.

Evaluation of different skin regions derived from a postmortem jaguar, Panthera onca (Linnaeus, 1758), after vitrification for development of cryobanks from captive animals

Biological resource banks represent valuable tools for the conservation of species vulnerable to extinction, such as the jaguar. Cryobanks of skins have the potential to safeguard rare genotypes, allowing the potential exploitation of biological samples in animal multiplication technologies and the study of genetic variability. Determination of the most suitable skin regions for tissue conservation can help increase the efficiency of cryobanks and the storage of biological samples. To this end, we evaluated the effects of vitrification of skin tissues from the ear, caudal, and femoral regions of a post-mortem jaguar belonging to a zoo in Brazil. Non-vitrified and vitrified samples were evaluated and compared using quantitative methods, focusing on skin thickness, cell quantification, number of perinuclear halos, collagen and elastic density, and proliferative activity. No differences were observed in skin thickness, number of perinuclear halos, elastic density, and proliferative activity between non-vitrified and vitrified tissues in skin from any region. However, vitrified tissues derived from femoral skin showed a reduction in the number of fibroblasts, epidermal cells and collagen density compared to non-vitrified tissues. In summary, the ear and caudal regions provided the best conservation of somatic tissues derived from jaguars, and skin samples from these regions are therefore the most suitable for the formation of cryobanks.

The perspective of the incompatible of nucleus and mitochondria in interspecies somatic cell nuclear transfer for endangered species

Taking into account the latest Red List of the International Union for Conservation of Nature in which 25% of all mammals are threatened with extinction, somatic cell nuclear transfer (SCNT) could be a beneficial tool and holds a lot of potential for aiding the conservation of endangered, exotic or even extinct animal species if somatic cells of such animals are available. In the case of shortage and sparse amount of wild animal oocytes, interspecies somatic cell nuclear transfer (iSCNT), where the recipient ooplasm and donor nucleus are derived from different species, is the alternative SCNT technique. The successful application of iSCNT, resulting in the production of live offspring, was confirmed in several combination of closely related species. When nucleus donor cells and recipient oocytes have been used in many other combinations, very often with a very distant taxonomical relation iSCNT resulted only in the very early stages of cloned embryo development. Problems encountered during iSCNT related to mitochondrial DNA (mtDNA)/genomic DNA incompatibility, mtDNA heteroplasmy, embryonic genome activation of the donor nucleus by the recipient oocyte and availability of suitable foster mothers for iSCNT embryos. Implementing assisted reproductive technologies, including iSCNT, to conservation programmes also raises concerns that the production of genetically identical populations might cause problems with inbreeding. The article aims at presenting achievements, limitations and perspectives of iSCNT in maintaining animal biodiversity.

Embryo aggregation allows the production of kodkod (Leopardus guigna) blastocysts after interspecific SCNT

The kodkod (Leopardus guigna) is a small felid endemic of Chile and is considered a vulnerable species. Domestic cat oocytes have been successfully used as recipient cytoplast to reprogram somatic cells from different felids by interspecific somatic cell nuclear transfer (iSCNT). The developmental competence of felid embryos generated by iSCNT can be improved by the aggregation method using a zona-free culture system. The objective of this research was to evaluate the developmental competence of kodkod embryos generated by iSCNT using domestic cat oocytes and the aggregation method. For this purpose, five experimental group were done: (1) cat embryos generated by IVF, (2) cat embryos generated by SCNT (Ca1x), (3) aggregated cat embryos generated by SCNT (Ca2x), (4) kodkod embryos generated by iSCNT (K1x) and (5) aggregated kodkod embryos generated by iSCNT (K2x). Cleavage, morulae and blastocyst rates were estimated. The blastocyst diameter was evaluated. The gene expression level of pluripotency (OCT4, SOX2 and NANOG) and differentiation markers (CDX2 and GATA6) was analyzed in blastocysts. Morulae rate was higher in the IVF group and when cloned embryos were cultured in aggregates (IVF: 68.2%, Ca2x: 58.0% and K2x: 62.4%) compared to individually cultured kodkod embryos (K1x: 37.0%) (P < 0.05). Embryo aggregation increased blastocysts formation in the Ca2x group (30.9%) to a similar rate compared to the IVF group (44.5%) (P > 0.05). No blastocysts were generated in the K1x group, whereas blastocysts formation was obtained in K2x group (5.9%). The diameter of blastocysts from the K2x group (172.8 μm) was significantly lower than blastocysts from the Ca2x group (P < 0.05). The relative expression of OCT4 was lower in blastocysts from Ca1x than in blastocysts from IVF (P < 0.05). Furthermore, CDX2 expression was lower in blastocysts from Ca2x than in blastocysts from Ca1x and IVF groups (P < 0.05). In kodkod embryos, only one blastocyst from the K2x group expressed OCT4. No expression of SOX2, NANOG, CDX2 and GATA6 was detected in kodkod blastocysts. In conclusion, after iSCNT, domestic cat oocytes support the development of kodkod embryos until the morula stage. The aggregation method increases the morulae rate of kodkod cloned embryos and allows blastocysts formation. However, kodkod blastocysts have a poor morphological quality and a lacking expression of pluripotency and differentiation markers, probably caused by an incomplete nuclear reprogramming.

A Comparative Approach of Cellular Reprogramming in the Rodentia Order

Cellular reprogramming mainly involves induction of reactivation of genes responsible for nuclear plasticity, a process that can be performed in vitro through production of cloned embryos by somatic cell nuclear transfer or by induction of cells into the pluripotent state through exogenous transcription factor expression. While these techniques are already well known and utilized in mice and rats, their application in other rodent species would be greatly beneficial, especially for conservation purposes. Within the diverse Rodentia order, wild species stand out as they play an important role in balancing the ecosystem by facilitating seed diversion, soil aeration, and consequently, reforestation. Many of these species are currently approaching extinction, and application of techniques, such as nuclear reprogramming, aimed at species conservation and multiplication and to produce stem cells is of interest. Thus, in this review, we aimed to present the evolution and success of nuclear reprogramming, mainly highlighting its potential application for the conservation of wild rodents.

Assessing the effect of interspecies oocyte nucleolar material dosage on embryonic development

Sequence differences are considered to be the basic cause of developmental failure in interspecies embryos when more distant species are combined. However, other phenomena, such as insufficient or excessive quantity of specific cellular factors, might also influence the outcome. These effects are usually not considered. One of the organelles shown to contain different amount of proteins is the oocyte nucleolus-like body. Here we show that upon interspecies transfer, a single porcine nucleolus-like body is unable to support the development of a mouse parthenogenetic embryo derived from an enucleolated oocyte. However, when the amount of the porcine nucleolar material is increased to equalize the amount of mouse nucleolar material by transferring two nucleolus-like bodies, mouse embryos are able to pass the developmental block elicited by enucleolation. These embryos progress to the blastocyst stage at rates comparable to controls. Thus, using the model of an interspecies nucleolus-like body transplantation between mouse and pig oocytes, we show that an inadequate amount of nucleolar factors, rather than the species origin, affects the development. In a wider context of interspecies nuclear transfer schemes, the observed incompatibility between more distant species might not stem simply from sequence differences but also from improper dosage of key cellular factors.

Isolation, characterization, and cryopreservation of collared peccary skin-derived fibroblast cell lines

Background

Biobanking of cell lines is a promising tool of support for wildlife conservation. In particular, the ability to preserve fibroblast cell lines derived from collared peccaries is of significance as these wild mammals are unique to the Americas and play a large role in maintaining the ecosystem. We identified collared peccary fibroblasts by immunofluorescence and evaluated their morphology, growth and adherence capacity. Further, we monitored the viability and metabolic activity of the fibroblasts to determine the effects of passage number and cryopreservation on establishment of cell lines.

Methods

Skin biopsies were collected from the peripheral ear region from five adult animals in captivity. Initially, cells were isolated from fragments and cultured in the Dulbecco's modified Eagle medium supplemented with 10% fetal bovine serum and 2% antibiotic-antimycotic solution under a controlled atmosphere (38.5 °C, 5% CO₂). We evaluated the maintenance of primary cells for morphology, adherence capacity of explants, explants in subconfluence, cell growth and absence of contamination. Moreover, we identified the fibroblast cells by immunofluorescence. Additionally, to evaluate the influence of the number of passages (first, third and tenth passage) and cryopreservation on establishment of cell lines, fibroblasts were analysed for the viability, metabolic activity, population doubling time (PDT), levels of reactive oxygen species (ROS), and mitochondrial membrane potential (ΔΨm).

Results

All explants (20/20) adhered to the dish in 2.4 days ± 0.5 with growth around the explants in 4.6 days ± 0.7, and subconfluence was observed within 7.8 days ± 1.0. Moreover, by morphology and immunocytochemistry analyses, cells were identified as fibroblasts which presented oval nuclei, a fusiform shape and positive vimentin staining. No contamination was observed after culture without antibiotics and antifungals for 30 days. While there was no difference observed for cell viability after the passages (first vs. third: P = 0.98; first vs. tenth: P = 0.76; third vs. tenth: P = 0.85), metabolic activity was found to be reduced in the tenth passage (23.2 ± 12.1%) when compared to that in the first and third passage (100.0 ± 24.4%, P = 0.006). Moreover, the cryopreservation did not influence the viability (P = 0.11), metabolic activity (P = 0.77), or PDT (P = 0.11). Nevertheless, a greater ΔΨm (P = 0.0001) was observed for the cryopreserved cells (2.12 ± 0.14) when compared to that in the non-cryopreserved cells (1.00 ± 0.05). Additionally, the cryopreserved cells showed greater levels of intracellular ROS after thawing (1.69 ± 0.38 vs. 1.00 ± 0.22, P = 0.04).

Conclusions

This study is the first report on isolation, characterization and cryopreservation of fibroblasts from collared peccaries. We showed that adherent cultures were efficient for obtaining fibroblasts, which can be used as donor cells for nuclei for species cloning and other applications.

Production of collared peccary (Pecari tajacu Linnaeus, 1758) parthenogenic embryos following different oocyte chemical activation and in vitro maturation conditions

To optimize the protocols for assisted reproductive techniques (ARTs) in collared peccary (Pecari tajacu Linnaeus, 1758), we evaluated various conditions for oocyte in vitro maturation (IVM) and chemical activation. Initially, we assessed the IVM rates, cumulus-oocyte complex (COC) quality, and oocyte morphometry in the absence or presence of epidermal growth factor (EGF). There was no difference between the COCs matured in absence or presence of EGF for the expansion of cumulus cells (97.6% ± 1.2 vs. 100% ± 0.0), presence of first polar body (65.9% ± 1.2 vs. 70.5% ± 1.8), nuclear status in second metaphase (62.5% ± 11.6 vs. 68.4% ± 4.9), cytoplasmic maturation (100.0% ± 0.7 vs. 75.0% ± 0.7), reactive oxygen species levels (0.5 ± 0.2 vs. 0.3 ± 0.1), and mitochondrial membrane potential (1.1 ± 0.2 vs. 1.1 ± 0.1). However, the zona pellucida thickness of matured COCs was reduced in the presence of EGF. Thus, the EGF group was used for further experiments. The oocytes were artificially activated with ionomycin and four secondary activator combinations [6-dimethylaminopurine (6D), 6D and cytochalasin B (6D + CB), cycloheximide (CHX), and CHX and CB (CHX + CB)]. The effect of immature COCs based on cumulus cell layers and cytoplasm homogeneity (GI and GII or GIII COCs) on embryonic development and quality was evaluated. There was no difference in the cleavage rates among the groups of secondary activators. The cleavage rates of embryos derived from GI/GII and GIII COCs were greater than 72.2% and 25.0%, respectively. Moreover, treatment with CHX showed a reduction in the cleavage rate of embryos derived from GIII COCs when compared to the cleavage rate of embryos derived from GI/GII COCs (P < 0.05). Nevertheless, higher rates of blastocyst/total GI and GII COCs were observed in the 6D group (27.6% ± 0.3) compared to CHX group (6.9% ± 0.3). Additionally, only 6D treatment resulted in the production of embryos derived from GIII COCs (25.0% ± 0.2). The percentage of the ICM/total cell ratio was also greater in blastocysts derived from 6D (42.5% ± 19.0), 6D + CB (37.9% ± 21.9), and CHX + CB (43.8% ± 19.6) groups when compared to CHX (3.6% ± 0.1) group. Thus, the combination of ionomycin and 6D could produce collared peccary embryos by activation of both GI/GII COCs and GIII COCs. These optimized IVM conditions using EGF and chemical activation using ionomycin and 6D in collared peccaries form the first steps for establishing ARTs to conserve this species.