AANAT transgenic sheep generated via OPS vitrified-microinjected pronuclear embryos and reproduction efficiency of the transgenic offspring

Genome editing: An insight into disease resistance, production efficiency, and biomedical applications in livestock

One of the primary concerns for the survival of the human species is the growing demand for food brought on by an increasing global population. New developments in genome-editing technology present promising opportunities for the growth of wholesome and prolific farm animals. Genome editing in large animals is used for a variety of purposes, including biotechnology to improve food production, animal health, and pest management, as well as the development of animal models for fundamental research and biomedicine. Genome editing entails modifying genetic material by removing, adding, or manipulating particular DNA sequences from a particular locus in a way that does not happen naturally. The three primary genome editors are CRISPR/Cas 9, TALENs, and ZFNs. Each of these enzymes is capable of precisely severing nuclear DNA at a predetermined location. One of the most effective inventions is base editing, which enables single base conversions without the requirement for a DNA double-strand break (DSB). As reliable methods for precise genome editing in studies involving animals, cytosine and adenine base editing are now well-established. Effective zygote editing with both cytosine and adenine base editors (ABE) has resulted in the production of animal models. Both base editors produced comparable outcomes for the precise editing of point mutations in somatic cells, advancing the field of gene therapy. This review focused on the principles, methods, recent developments, outstanding applications, the advantages and disadvantages of ZFNs, TALENs, and CRISPR/Cas9 base editors, and prime editing in diverse lab and farm animals. Additionally, we address the methodologies that can be used for gene regulation, base editing, and epigenetic alterations, as well as the significance of genome editing in animal models to better reflect real disease. We also look at methods designed to increase the effectiveness and precision of gene editing tools. Genome editing in large animals is used for a variety of purposes, including biotechnology to improve food production, animal health, and pest management, as well as the development of animal models for fundamental research and biomedicine. This review is an overview of the existing knowledge of the principles, methods, recent developments, outstanding applications, the advantages and disadvantages of zinc finger nucleases (ZFNs), transcription-activator-like endonucleases (TALENs), and clustered regularly interspaced short palindromic repeats associated protein 9 (CRISPR/Cas 9), base editors and prime editing in diverse lab and farm animals, which will offer better and healthier products for the entire human race.

Recent advances of oocyte/embryo vitrification in mammals from rodents and large animals

Vitrification is a valuable technology that enables semipermanent preservation and long-distance or international transportation of genetically modified and native animals. In laboratory mice, vitrification maintains and transports embryos, and many institutions and companies sell vitrified embryos. In contrast, despite numerous papers reporting on vitrification in livestock over the past decade, practical implementation has yet to be achieved. However, with advances in genome editing technology, it is anticipated that the number of genetically modified domestic animals will increase, leading to a rise in demand for vitrification of oocytes and embryos. Here, we provide an objective overview of recent advancements in vitrification technology for livestock, drawing a comparison with the current developments in laboratory animals. Additionally, we explore the future prospects for vitrification in livestock, focusing on its potential benefits and drawbacks.

Refinements in embryo manipulation applied to CRISPR technology in livestock

The implementation of CRISPR technology in large animals requires further improvements in embryo manipulation and transfer to be applied with commercial purposes. In this study we report (a) developmental competence of CRISPR/Cas microinjected zygotes subjected to in vitro culture in large scale programs in sheep; (b) pregnancy outcomes after early-stage (2-8-cell) embryo transfer into the oviduct or the uterine horn; and (c) embryo survival and birth rate after vitrification/warming of CRISPR/Cas microinjected zygotes. Experiment 1 consisted of a retrospective analysis to evaluate embryo developmental rate of in vitro produced zygotes subjected to CRISPR/Cas microinjection (n = 7,819) compared with a subset of non-microinjected zygotes (n = 701). Development rates to blastocyst on Day 6 were 20.0% for microinjected zygotes and 44.9% for non-injected zygotes (P < 0.05). In Experiment 2, CRISPR/Cas microinjected zygotes were transferred on Day 2 after in vitro fertilization (2-8 cell embryos) into the oviductal ampulla (n = 262) or into the uterine horn (n = 276) in synchronized recipient ewes at prefixed time (i.e., approximately two days after ovulation). Pregnant/transferred recipients (24.0% vs. 25.0%), embryo survival/transferred embryos (6.9% vs. 6.2%), and born lambs/pregnant embryos (72.2% vs. 100.0%) did not differ significantly in the two groups. In Experiment 3, CRISPR/Cas microinjected zygotes were maintained under in vitro culture until blastocyst stage (Day 6), and subjected to vitrification/warming via the Cryotop method (n = 474), while a subset of embryos were left fresh as control group (n = 75). Embryos were transferred into the uterine horn of recipient females at prefixed time 8.5 days after the estrous synchronization treatment (i.e., approximately six days after ovulation). Pregnancy rate (30.8% vs. 48.0%), embryo survival rate (14.8% vs. 21.3%), and birth rate (85.7% vs. 75.0%) were not different (PNS) between vitrified and fresh embryos, respectively. In conclusion, the current study in sheep embryos reports (a) suitable developmental rate after CRISPR/Cas microinjection (i.e., 20%), even though it was lower than non-microinjected zygotes; (b) similar outcomes when Day 2-embryos were placed into the uterine horn instead of the oviduct, avoiding both time-consuming and invasive oviduct manipulation, and extended in vitro culture during one week; (c) promising pregnancy and birth rates obtained with vitrification of CRISPR/Cas microinjected embryos. This knowledge on in vitro embryo development, timing of embryo transfer, and cryopreservation of CRISPR/Cas microinjected zygotes have practical implications for the implementation of genome editing technology in large animals.

Investigation of SNP markers for the melatonin production trait in the Hu sheep with bulked segregant analysis

BACKGROUND

As an important reproductive hormone, melatonin plays an important role in regulating the reproductive activities of sheep and other mammals. Hu sheep is a breed favoring for meat, with prolific traits. In order to explore the relationship between melatonin and reproductive function of Hu sheep, 7,694,759 SNPs were screened out through the whole genome sequencing analysis from high and low melatonin production Hu sheep.

RESULTS

A total of 68,673 SNPs, involving in 1126 genes, were identified by ED association analysis. Correlation analysis of SNPs of AANAT/ASMT gene and MTNR1A/MTNR1B gene were carried out. The melatonin level of CG genotype 7,981,372 of AANAT, GA genotype 7,981,866 of ASMT and GG genotype 17,355,171 of MTNR1A were higher than the average melatonin level of 1.64 ng/mL. High melatonin Hu sheep appear to have better multiple reproductive performance.

CONCLUSIONS

By using different methods, three SNPs which are associated with high melatonin production trait have been identified in Hu sheep. These 3 SNPs are located in melatonin synthetase AANAT/ASMT and receptor MTNR1A, respectively. Considering the positive association between melatonin production and reproductive performance in ruminants, these three SNPs can be served as the potential molecular markers for breading Hu sheep with the desirable reproductive traits.

Whole-genome methylation analysis reveals epigenetic variation between wild-type and nontransgenic cloned, ASMT transgenic cloned dairy goats generated by the somatic cell nuclear transfer

BACKGROUND

SCNT (somatic cell nuclear transfer) is of great significance to biological research and also to the livestock breeding. However, the survival rate of the SCNT cloned animals is relatively low compared to other transgenic methods. This indicates the potential epigenetic variations between them. DNA methylation is a key marker of mammalian epigenetics and its alterations will lead to phenotypic differences. In this study, ASMT (acetylserotonin-O-methyltransferase) ovarian overexpression transgenic goat was produced by using SCNT. To investigate whether there are epigenetic differences between cloned and WT (wild type) goats, WGBS (whole-genome bisulfite sequencing) was used to measure the whole-genome methylation of these animals.

RESULTS

It is observed that the different mCpG sites are mainly present in the intergenic and intronic regions between cloned and WT animals, and their CG-type methylation sites are strongly correlated. DMR (differentially methylated region) lengths are located around 1000 bp, mainly distributed in the exonic, intergenic and intronic functional domains. A total of 56 and 36 DMGs (differentially methylated genes) were identified by GO and KEGG databases, respectively. Functional annotation showed that DMGs were enriched in biological-process, cellular-component, molecular-function and other signaling pathways. A total of 10 identical genes related to growth and development were identified in GO and KEGG databases.

CONCLUSION

The differences in methylation genes among the tested animals have been identified. A total of 10 DMGs associated with growth and development were identified between cloned and WT animals. The results indicate that the differential patterns of DNA methylation between the cloned and WT goats are probably caused by the SCNT. These novel observations will help us to further identify the unveiled mechanisms of somatic cell cloning technology, particularly in goats.

Redesigning small ruminant genomes with CRISPR toolkit: Overview and perspectives

Genetic modification is a rapidly developing field in which numerous significant breakthroughs have been achieved. Over the last few decades, genetic modification has evolved from insertional transgenesis to gene targeting and editing and, more recently, to base and prime editing using CRISPR-derived systems. Currently, CRISPR-based genome editing systems are showing great potential for generating gene-edited offspring with defined genetic characteristics. Domestic small ruminants (sheep and goats) have shown great potential as large animal models for genome engineering. Ovine and caprine genomes have been engineered using CRISPR-based systems for numerous purposes. These include generating superior agricultural breeds, expression of therapeutic agents in mammary glands, and developing animal models to be used in the study of human genetic disorders and regenerative medicine. The creation of these models has been facilitated by the continuous emergence and development of genetic modification tools. In this review, we provide an overview on how CRISPR-based systems have been used in the generation of gene-edited small ruminants through the two main pathways (embryonic microinjection and somatic cell nuclear transfer) and highlight the ovine and caprine genes that have been targeted via knockout, knockin, HDR-mediated point mutation, and base editing approaches, as well as the aims of these specific manipulations.

Genetically Engineered Pigs to Study Cancer

Recent decades have seen groundbreaking advances in cancer research. Genetically engineered animal models, mainly in mice, have contributed to a better understanding of the underlying mechanisms involved in cancer. However, mice are not ideal for translating basic research into studies closer to the clinic. There is a need for complementary information provided by non-rodent species. Pigs are well suited for translational biomedical research as they share many similarities with humans such as body and organ size, aspects of anatomy, physiology and pathophysiology and can provide valuable means of developing and testing novel diagnostic and therapeutic procedures. Porcine oncology is a new field, but it is clear that replication of key oncogenic mutation in pigs can usefully mimic several human cancers. This review briefly outlines the technology used to generate genetically modified pigs, provides an overview of existing cancer models, their applications and how the field may develop in the near future.

Sheep and Goat Genome Engineering: From Random Transgenesis to the CRISPR Era

Sheep and goats are valuable livestock species that have been raised for their production of meat, milk, fiber, and other by-products. Due to their suitable size, short gestation period, and abundant secretion of milk, sheep and goats have become important model animals in agricultural, pharmaceutical, and biomedical research. Genome engineering has been widely applied to sheep and goat research. Pronuclear injection and somatic cell nuclear transfer represent the two primary procedures for the generation of genetically modified sheep and goats. Further assisted tools have emerged to enhance the efficiency of genetic modification and to simplify the generation of genetically modified founders. These tools include sperm-mediated gene transfer, viral vectors, RNA interference, recombinases, transposons, and endonucleases. Of these tools, the four classes of site-specific endonucleases (meganucleases, ZFNs, TALENs, and CRISPRs) have attracted wide attention due to their DNA double-strand break-inducing role, which enable desired DNA modifications based on the stimulation of native cellular DNA repair mechanisms. Currently, CRISPR systems dominate the field of genome editing. Gene-edited sheep and goats, generated using these tools, provide valuable models for investigations on gene functions, improving animal breeding, producing pharmaceuticals in milk, improving animal disease resistance, recapitulating human diseases, and providing hosts for the growth of human organs. In addition, more promising derivative tools of CRISPR systems have emerged such as base editors which enable the induction of single-base alterations without any requirements for homology-directed repair or DNA donor. These precise editors are helpful for revealing desirable phenotypes and correcting genetic diseases controlled by single bases. This review highlights the advances of genome engineering in sheep and goats over the past four decades with particular emphasis on the application of CRISPR/Cas9 systems.