Propagation of elite rescue dogs by somatic cell nuclear transfer

Accomplishment of canine cloning through in vitro matured oocytes: a pioneering milestone

The in vitro maturation (IVM) rate of canine oocytes remains low compared to other mammals due to their unique reproductive characteristics. This study aimed to explore the effect of hormone supplementation during the IVM of canine immature oocytes on nuclear maturation and subsequently assess its potential application in canine somatic cell nuclear transfer (SCNT). Immature oocytes were collected and cultured in an IVM medium supplemented with hormones (follicle-stimulating hormone [FSH] and progesterone [P4]) or without hormones (control) for 24 hours. The maturation rates of oocytes in the hormone-treated group (94.92 ± 3.15%) were significantly higher than those in the control group (61.01 ± 4.23%). Both in vitro and in vivo matured oocytes underwent NT to evaluate their utility, and the fusion rates were higher in the in vitro matured group than those in the vivo matured group, not significant between in vivo and in vitro matured group (73.28% and 82.35%, respectively). As a result, 14 fused embryos from the in vitro matured group were transferred into two surrogates, with one surrogate achieving a successful pregnancy and delivering four puppies. Whereas in the in vivo matured group, 85 fused embryos were transferred to 8 surrogate mothers, leading to three surrogates becoming pregnant and delivering one, four, and two puppies. The pregnancy rates were not significant between both groups (50% and 37.50%), but the number of offspring exhibited a significant difference (28.57% and 8.23%). In conclusion, we achieved a remarkable milestone by successfully producing cloned puppies using in vitro matured oocytes, underscoring the feasibility of canine cloning from in vitro recovered oocytes. It is important to note that this study focused only on immature oocytes after ovulation and only during the estrus stage. Further research targeting other stages of the estrous cycle could potentially enhance canine cloning efficiency.

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.

Whole Blood Transcriptome Analysis for Lifelong Monitoring in Elite Sniffer Dogs Produced by Somatic Cell Nuclear Transfer

Reproductive cloning by somatic cell nuclear transfer (SCNT) is a valuable method to propagate service dogs with desirable traits because of higher selection rates in cloned dogs. However, incomplete reprogramming is a major barrier to SCNT, and the assessment of reprogramming is limited to preimplantation embryos and tissues from dead and/or adult tissue. Thus, lifelong monitoring in SCNT dogs can be useful to evaluate the SCNT service dogs for propagation. We applied microarray and qRT-PCR to profile of mRNA and miRNA in whole blood samples collected from four cloned dogs (S), three age-matched control dogs (A), and a donor dog (D). In the analysis of differentially expressed genes in S-A, A-D, and S-D pairs, most genomes were completely reprogrammed and rejuvenated in the cloned offspring. However, several RNAs were differentially expressed. Interestingly, the altered genes are associated with aging and senescence. Furthermore, we identified potential biomarkers such as mirR-223 (NFIB; CLIC4), miRN-494 (ARHGEF12), miR-106b (PPP1R3B; CC2D1A), miR-20a (CC2D1A; PPP1R3B), miR-30e (IGJ; HIRA), and miR-19a (TNRC6A) by miRNA-target mRNA pairing for monitoring rejuvenation, aging/senescence, and reprogramming in cloned dogs. The novel comparative transcriptomic information about SCNT and age-matched dogs can be used to assess the lifelong health of cloned dogs and to facilitate the selection of training animals with minimal invasive procedures.

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.

Suberoylanilide hydroxamic acid during in vitro culture improves development of dog-pig interspecies cloned embryos but not dog cloned embryos

This study was conducted to investigate whether the treatment of dog to pig interspecies somatic cell nuclear transfer (iSCNT) embryos with a histone deacetylase inhibitor, to improve nuclear reprogramming, can be applied to dog SCNT embryos. The dog to pig iSCNT embryos were cultured in fresh porcine zygote medium-5 (PZM-5) with 0, 1, or 10 µM suberoylanilide hydroxamic acid (SAHA) for 6 h, then transferred to PZM-5 without SAHA. Although there were no significant differences in cleavage rates, the rates of 5-8-cell stage embryo development were significantly higher in the 10 µM group (19.5 ± 0.8%) compared to the 0 µM groups (13.4 ± 0.8%). Acetylation of H3K9 was also significantly higher in embryos beyond the 4-cell stage in the 10 µM group compared to the 0 or 1 µM groups. Treatment with 10 µM SAHA for 6 h was chosen for application to dog SCNT. Dog cloned embryos with 0 or 10 µM SAHA were transferred to recipients. However, there were no significant differences in pregnancy and delivery rates between the two groups. Therefore, it can be concluded that although porcine oocytes support nuclear reprogramming of dog fibroblasts, treatment with a histone deacetylase inhibitor that supports nuclear reprogramming in dog to pig iSCNT embryos was not sufficient for reprogramming in dog SCNT embryos.

Effect of co-culture canine cumulus and oviduct cells with porcine oocytes during maturation and subsequent embryo development of parthenotes in vitro

In the estrus stage, canine oocytes are surrounded by cumulus cells and undergo maturation in the oviduct for 2-3 days after ovulation. We hypothesized that canine oviduct cells (cOC) and canine cumulus cells (cCC) during this stage might affect the maturation of oocytes and thereby improve subsequent embryo development. Therefore, the objective of this study was to compare the effects of a cOC and cCC co-culture on oocyte in vitro maturation (IVM) and subsequent embryo development, and to analyze the gene expressions in a molecular fashion what co-culture actually gives the specific pathways in which the co-culture cells act to improve maturation and embryo development. The effect of co-culture using cOC and cCC on porcine oocyte IVM was investigated. Thereafter, oocytes were activated using electrical stimulation and embryo developmental competence was estimated. The expression of the genes related to oocyte maturation, embryo development and apoptosis were analyzed. Also, reactive oxygen species (ROS) levels after IVM was analyzed. The IVM rate and embryo development including cleavage, blastocyst formation rates, and total blastocyst cell numbers from cOC group were significantly higher than other groups (P < 0.05). The expression of SMAD2/3 and growth differentiation factor 9 (GDF9) was significantly increased in cOC and oocytes from the cOC group compared with other groups. Moreover, the levels of GDF9, prostaglandin-endoperoxide synthase 2 (PTGS2), WNT3A and matrix metalloproteinase 2 (MMP2) were significantly up-regulated in blastocysts from the cOC group. The concentration of ROS was significantly lower in the supernatant of cOC groups compared with other groups. Also, the expression of BCL2 was significantly increased in porcine cumulus cells and oocytes from cOC group. The present study demonstrated that co-culture with cOC improved in vitro porcine oocyte maturation and subsequent embryo development competence. Also, co-culture with cOC during IVM induces a suitable environment for oocyte maturation by enhancing the mRNA level of SMAD2/3 and GDF9, and for embryo development by elevating the expression level of PTGS2, WNT3A and MMP2. In addition, the decreased ROS level in cOC co-culture could have a beneficial influence on oocyte maturation.