Origin and population structure of native dog breeds in the Korean peninsula and East Asia

To study the ancestry and phylogenetic relationships of native Korean dog breeds to other Asian dog populations, we analyzed nucleotide variations in whole-genome sequences of 205 canid individuals. Sapsaree, Northern Chinese indigenous dog, and Tibetan Mastiff were largely related to West Eurasian ancestry. Jindo, Donggyeongi, Shiba, Southern Chinese indigenous (SCHI), Vietnamese indigenous dogs (VIET), and Indonesian indigenous dogs were related to Southeast and East Asian ancestry. Among East Asian dog breeds, Sapsaree presented the highest haplotype sharing with German Shepherds, indicating ancient admixture of European ancestry to modern East Asian dog breeds. SCHI showed greater haplotype sharing with New Guinea singing dogs, VIET, and Jindo than with other Asian breeds. The predicted divergence time of East Asian populations from their common ancestor was approximately 2,000 to 11,000 years ago. Our results expand understanding of the genetic history of dogs in the Korean peninsula to the Asian continent and Oceanic region.

Generation of genome-edited dogs by somatic cell nuclear transfer

Background

Canine cloning technology based on somatic cell nuclear transfer (SCNT) combined with genome-editing tools such as CRISPR-Cas9 can be used to correct pathogenic mutations in purebred dogs or to generate animal models of disease.

Results

We constructed a CRISPR-Cas9 vector targeting canine DJ-1. Genome-edited canine fibroblasts were established using vector transfection and antibiotic selection. We performed canine SCNT using genome-edited fibroblasts and successfully generated two genome-edited dogs. Both genome-edited dogs had insertion-deletion mutations at the target locus, and DJ-1 expression was either downregulated or completely repressed.

Conclusion

SCNT successfully produced genome-edited dogs by using the CRISPR-Cas9 system for the first time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-022-00749-3.

Dog cloning-no longer science fiction

Since the generation of world's first cloned dog, Snuppy, in 2005, somatic cell nuclear transfer (SCNT) in dogs has been widely applied for producing several kinds of dogs with specific objectives. Previous studies have demonstrated that cloned dogs show normal characteristics in growth, blood parameters and behavioural aspect. Also, canine SCNT technique has been applied to propagate working dogs with excellent abilities in fields such as assistance of disabled people, drugs detection and rescue activity. Because dogs have similar habituation properties and share many characteristics including anatomic and physiological aspects with humans, they are also primary candidates for human disease models. Recently, transgenic dogs that express red fluorescent protein gene constitutively and green fluorescent protein gene conditionally have been generated. In addition, transgenic dogs with an overexpression of peroxisome proliferator-activated receptor-alpha in specific muscles were generated to enhance physical performance. In 2017, Snuppy was recloned with markedly increased pregnancy and delivery rates compared to the statistics from when Snuppy was first cloned. Such striking improvements in the cloning of dogs using SCNT procedures suggest that dog cloning could be applied in many fields of biomedical science for human diseases research, and the application of cloning is no longer science fiction.

Health and temperaments of cloned working dogs

Dogs serve human society in various ways by working at tasks that are based on their superior olfactory sensitivity. However, it has been reported that only about half of all trained dogs may qualify as working dogs through conventional breeding management because proper temperament and health are needed in addition to their innate scent detection ability. To overcome this low efficiency of breeding qualified working dogs, and to reduce the enormous costs of maintaining unqualified dogs, somatic cell nuclear transfer has been applied in the propagation of working dogs. Herein, we review the history of cloning working dogs and evaluate the health development, temperaments, and behavioral similarities among the cloned dogs. We also discuss concerns about dog cloning including those related to birth defects, lifespan, and cloning efficiency.

Reproductive ability of a cloned male detector dog and behavioral traits of its offspring

In 2007, seven detector dogs were produced by somatic cell nuclear transfer using one nuclear donor dog, then trained and certified as excellent detector dogs, similar to their donor. In 2011, we crossed a cloned male and normal female by natural breeding and produced ten offspring. In this study, we investigated the puppies' temperaments, which we later compared with those of the cloned parent male. The results show that the cloned male had normal reproductive abilities and produced healthy offspring. All puppies completed narcotic detector dog training with a success rate for selection of 60%. Although the litter of cloned males was small in this study, a cloned male dog bred by natural mating produced puppies that later successfully completed the training course for drug detection. In conclusion, cloning an elite dog with superior genetic factors and breeding of the cloned dog was found to be a useful method to efficiently procure detector dogs.

Cloning of the short-tailed Gyeongju Donggyeong dog via SCNT: conserving phenotypic inheritance

Somatic cell nuclear transfer is a useful tool to maintain genetic information of animals. The Gyeongju Donggyeong dog is a breed registered as natural monument in Korea. The unique feature of the Donggyeong dog is its tail, as the Donggyeong dog can be classified as either short tailed or tailless. The aim of this study was to preserve the Donggyeong dog’s unique feature by cloning. Fibroblasts were obtained from a short-tailed Donggyeong dog. In vivo matured oocytes were enucleated, microinjected with a donor cell and fused electrically. Reconstructed embryos were transferred to six recipient dogs. One surrogate became pregnant, and one short-tailed Donggyeong dog was delivered. This study demonstrated that the phenotype of the Donggyeong dog could be conserved by somatic cell nuclear transfer.

Altering histone acetylation status in donor cells with suberoylanilide hydroxamic acid does not affect dog cloning efficiency

Although dog cloning technology has been applied to conservation of endangered canids, propagation of elite dogs, and production of transgenic dogs, the efficiency of cloning is still very low. To help overcome this problem, we evaluated the effect of treating donor cells with suberoylanilide hydroxamic acid (SAHA), a histone deacetylase inhibitor, on dog cloning efficiency. Relative messenger RNA expressions of the bax1/bcl2 ratio and Dnmt1 in fibroblasts treated with different concentrations (0, 1, 10, 50 μM) of SAHA and durations (0, 20, 44 hours) were compared. Treatment with 1 μM for 20 hours showed significantly lower bax1/bcl2 and Dnmt1 transcript abundance. Acetylation of H3K9 was significantly increased after SAHA treatment, but H4K5, H4K8 and H4K16 were not changed. After SCNT using control or donor cells treated with SAHA, a total of 76 and 64 cloned embryos were transferred to seven and five recipients, respectively. Three fetuses were diagnosed in both control and SAHA-treated groups by ultrasonography 29 days after the embryo transfer, but there was no significant difference in the pregnancy rate (4.2% vs. 4.3%). In conclusion, although SAHA treatment as used in this study significantly decreased bax1/bcl2 and Dnmt1 transcripts of donor nuclei, as well as increased H3 acetylation, it was not enough to increase in vivo developmental competence of cloned dog embryos.

Species-specific challenges in dog cloning

Somatic cell nuclear transfer (SCNT) is now an established procedure used in cloning of several species. SCNT in dogs involves multiple steps including the removal of the nuclear material, injection of a donor cell, fusion, activation of the reconstructed oocytes and finally transfer to a synchronized female recipient. There are therefore many factors that contribute to cloning efficiency. By performing a retrospective analysis of 2005-2012 published papers regarding dog cloning, we define the optimum procedure and summarize the specific feature for dog cloning.

Reliability of Hoechst 33342 staining under wide-field microscopy for evaluation of the nuclear status of living dog oocytes

Due to the marked cytoplasmic opacity of canine oocytes, the diagnosis of their nuclear status is difficult. The objective of the present study was to evaluate the accuracy of Hoechst staining observed under epifluorescence wide-field microscopy [living oocyte observation (LivOO)] by comparison to a reference technique [DNA staining with ethidium homodimer-2 under confocal microscopy; fixed oocyte observation (FixOO)]. Four Hoechst 33342 concentrations (200 ng, 500 ng, 1 μg, 2 μg/mL) were tested and 1 μg/mL was the lowest one with the lowest proportion of oocytes in which DNA was missed. At this concentration, LivOO procedure did not affect the degeneration rate. On 379 oocytes observed individually with the two techniques successively, diagnosis of meiosis resumption by LivOO was exact in 87.3% of the cases, but the meiosis resumption rate was underestimated (23.5% versus 34.3% with FixOO; p < 0.001). Diagnosis for metaphase II was exact in 80% of the cases, but LivOO detected only 72.7% of the metaphase II oocytes present. Metaphase rates did not differ between LivOO and FixOO. This study contributes to a better interpretation of in vitro maturation results. The developmental potential of metaphase II canine oocytes sorted after Hoechst staining is to be evaluated.

Blastocysts cloned from the Putian Black pig ear tissues frozen without cryoprotectant at -80 and -196 degrees Celsius for 3 yrs

The Putian Black pig, as one of elite cultivars of endemic species in China, has been on the verge of extinction and urgently needs protection. Somatic cell nuclear transfer (SCNT) and noncryoprotected frozen tissue technology have successfully resurrected several mammalian species. Therefore, this study explored the primary feasibility of conserving this breed using a combination of both technologies. Skin tissues obtained from the ears of adult Putian Black boars were frozen without cryoprotectant at -20, -80, or -196 °C and stored for 3 yrs. Primary cell culture, passage and subculture were performed on frozen samples after being rapidly thawed at 39 °C and on fresh pig ear tissues (control). Cloned embryos were reconstructed using fibroblasts (from frozen and fresh tissues) with enucleated oocytes. Live cell lines were obtained from tissues frozen at -80 and at -196 °C and appeared to have normal proliferative activity after passage; furthermore, they directed cloned embryos to develop to the blastocyst stage after nuclear transfer. We concluded that the population of Putian Black pig might be increased in the future by transferring cloned blastocysts into synchronized recipient pigs.

Changes in the somatotrophic axis in genetically identical dogs

Because cloned dogs are genetically identical, variations among these animals can be a useful tool to elucidate mechanisms underlying phenotypic differences. To estimate the influence of genetic factors on phenotypic variation, changes in concentration patterns of growth hormone (GH), insulin like growth factor-1 (IGF-1), and IGF binding protein 3 (IGFBP-3) were compared among cloned and age-matched control dogs. In addition, the concentrations of GH and IGF-1 following administration of growth hormone releasing hormone (GHRH) and somatostatin (SRIF) were measured in both groups. In comparing hormone profiles, the control dogs had larger standard deviations from the means for GH, IGF-1, and IGFBP-3 than the clones. Also, the mean concentration of IGFBP-3 in clones was significantly lower than in the controls between 7 to 12 months of age, whereas the IGFBP-3 changes in clones and controls followed the same pattern. GHRH induced increased serum growth hormone concentration both in clones and controls. However, the concentration of IGF-1 was lower in clones than in controls, and larger standard variations were noted in the control group. In conclusion, the measured traits were more homogeneous in cloned animals than in controls, so cloned animals could be valuable for assessing effects of genotype and environment interactions.

Embryo biotechnology in the dog: a review

Canine embryos are a scarce biological material because of difficulties in collecting in vivo-produced embryos and the inability, to date, to produce canine embryos in vitro. The procedure for the transfer of in vivo-produced embryos has not been developed adequately, with only six attempts reported in the literature that have resulted in the birth of 45 puppies. In vitro, the fertilisation rate is particularly low (∼10%) and the incidence of polyspermy particularly high. So far, no puppy has been obtained from an in vitro-produced embryo. In contrast, cloning of somatic cells has been used successfully over the past 4 years, with the birth of 41 puppies reported in the literature, a yield that is comparable to that for other mammalian species. Over the same period, canine embryonic stem sells and transgenic cloned dogs have been obtained. Thus, the latest reproductive technologies are further advanced than in vitro embryo production. The lack of fundamental studies on the specific features of reproductive physiology and developmental biology in the canine is regrettable in view of the increasing role of dogs in our society and of the current demand for new biological models in biomedical technology.