Long-term health and germline transmission in transgenic cattle following transposon-mediated gene transfer.

BACKGROUND: Transposon-mediated, non-viral gene delivery is a powerful tool for generating stable cell lines and transgenic animals. However, as multi-copy insertion is the preferred integration pattern, there is the potential for uncontrolled changes in endogenous gene expression and detrimental effects in cells or animals. Our group has previously reported on the generation of several transgenic cattle by using microinjection of the Sleeping Beauty (SB) and PiggyBac (PB) transposons and seeks to explore the long-term effects of this technology on cattle. RESULTS: Transgenic cattle, one female (SNU-SB-1) and one male (SNU-PB-1), reached over 36 months of age with no significant health issues and normal blood parameters. The detection of transgene integration and fluorescent signal in oocytes and sperm suggested the capacity for germline transmission in both of the founder animals. After natural breeding, the founder transgenic cow delivered a male calf and secreted milk containing fluorescent transgenic proteins. The calf expressed green fluorescent protein in primary cells from ear skin, with no significant change in overall genomic stability and blood parameters. Three sites of transgene integration were identified by next-generation sequencing of the calf's genome. CONCLUSIONS: Overall, these data demonstrate that transposon-mediated transgenesis can be applied to cattle without being detrimental to their long-term genomic stability or general health. We further suggest that this technology may be usefully applied in other fields, such as the generation of transgenic animal models.

Disruption of exogenous eGFP gene using RNA-guided endonuclease in bovine transgenic somatic cells.

Genome-editing technologies are considered to be an important tool for generating gene knockout cattle models. Here, we report highly efficient disruption of a chromosomally integrated eGFP gene in bovine somatic cells using RNA-guided endonucleases, a new class of programmable nucleases developed from a bacterial Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 system. In the present study, we obtained homogenously eGFP-expressing primary fibroblasts from cloned bovine transgenic embryonic tissues and employed them for further analysis. CRISPR/Cas9 plasmids specifically targeting the eGFP gene were transfected into the eGFP fibroblasts by electroporation. After 10 days of culture, more than 40% of the cells had lost eGFP expression in fluorescence activated cell sorting (FACS) analysis. Targeted sequences of the transfected cells were analyzed, and various small indel mutations (6-203 bp deletions) in the target sequence were found. The fibroblasts mutated with the CRISPR/Cas9 system were applied for somatic cell nuclear transfer, and the reconstructed embryos were successfully developed into the blastocyst stage. In conclusion, the CRISPR/Cas9 system was successfully utilized in bovine cells and cloned embryos. This will be a useful technique to develop livestock transgenesis for agricultural science.

A retrospective analysis of conception per embryo transfer in dairy cattle in South Korea.

The bovine embryo production industry has seen significant growth over the past two decades, particularly in the production of in vitro produced embryos. This growth, driven by advancements in cryopreservation, in vitro culture mediums, ovum pick-up (OPU) procedures, ultrasonography devices, and embryo transfer (ET) has been notable. Particularly, ET is crucial for disseminating high genetic merit and amplifying foreign breeds by importing frozen embryos. This retrospective study aimed to assess factors affecting conception per embryo transfer (CPET) in Holstein-Friesian cattle in South Korea from October 2008 to July 2022. We evaluated type of embryo breed, type of embryo production (fresh and frozen; in vitro and in vivo production), recipient conditions including estrus type, corpus luteum quality, parity (nulliparous heifers, primiparous, and multiparous cows), and the daily mean temperature-humidity index (THI) as an index for heat stress. Type of embryo breed and estrus had no significant impact on CPET. However, we observed higher CPET in recipients with good quality corpus luteum, nulliparous heifers, and surrogates receiving fresh in vitro and frozen in vivo embryos. Importantly, CPET was not adversely affected by mild heat stress conditions (up to daily mean THI 76), indicating that using frozen in vivo embryos produced by multiple ovulation embryo transfer and fresh in vitro embryos by OPU-ET can help alleviate the subfertility issues in dairy cattle caused by global warming in Korea.

Developmental competence and cryotolerance of caprine parthenogenetic embryos cultured in chemically defined media.

In animal reproduction technologies, the in vitro embryo culture system has advanced over the past few decades. However, in vitro cultured embryos still have reduced functional and physiological abilities compared with those from in vivo conditions, and many factors of oviduct and uterine environments have not yet been revealed. Here, we demonstrated the in vitro culture of domestic goat (Capra hircus) embryos using two types of culture media, modified synthetic oviductal fluid (mSOF) and a two-step chemically defined medium (DI/II). To obtain parthenogenetic goat embryos, oocytes were matured in vitro in tissue culture media-199 supplemented with 10% fetal bovine serum for 22 to 24 hours, and activated with 5 µM, Ca(2+) ionomycin for 4 minutes, followed by 1.9 mM, 6-dimethylaminopurine treatment for 4 hours. After 2 days of embryo culture in different culture media, there were no significant differences in cleavage rates (96.6% vs. 95.4% in mSOF vs. DI/II, respectively). However, the DI/II group showed improved development competence to blastocysts (64.6% vs. 82.3% in mSOF vs. DI/II, respectively) and the total cell number of blastocysts (144.3 ± 9.2 vs. 264.4 ± 15.2 in mSOF vs. DI/II, respectively) at Day 7. After the cryopreservation of early-stage blastocysts at Day 6 via the conventional slow-freezing procedure, the surviving embryos were analyzed. The re-expansion rate after freezing and thawing was significantly higher in DI/II (39.66% vs. 67.69% in mSOF vs. DI/II, respectively), but there were no statistical differences in total cell numbers (142.3 ± 12.1 vs. 172.1 ± 11.6 in mSOF vs. DI/II, respectively), apoptotic index (4.9 ± 0.8% vs. 3.8 ± 0.7 in mSOF vs. DI/II, respectively), and the gene expression levels (BAX, GLUT1, MnSOD, and OCT4) among the re-expanded blastocysts. Overall, our data reported that the defined in vitro culture media for goat embryos were established with high efficiency, which will be very useful for goat embryo production.

Efficient generation of transgenic cattle using the DNA transposon and their analysis by next-generation sequencing.

Here, we efficiently generated transgenic cattle using two transposon systems (Sleeping Beauty and Piggybac) and their genomes were analyzed by next-generation sequencing (NGS). Blastocysts derived from microinjection of DNA transposons were selected and transferred into recipient cows. Nine transgenic cattle have been generated and grown-up to date without any health issues except two. Some of them expressed strong fluorescence and the transgene in the oocytes from a superovulating one were detected by PCR and sequencing. To investigate genomic variants by the transgene transposition, whole genomic DNA were analyzed by NGS. We found that preferred transposable integration (TA or TTAA) was identified in their genome. Even though multi-copies (i.e. fifteen) were confirmed, there was no significant difference in genome instabilities. In conclusion, we demonstrated that transgenic cattle using the DNA transposon system could be efficiently generated, and all those animals could be a valuable resource for agriculture and veterinary science.

Influence of factors during superovulation on embryo production in Korean Holstein cattle.

The aim of this study was to investigate the influence of key parameters (donor parity, milk production, post-parturient day, season and milk recording data) associated with efficiency of embryo recovery (ER) in Holstein cattle. Elite Holstein cows and heifers were selected for ER, while Holstein heifers were used as recipients. The numbers of transferable embryos (TEs) produced were not significantly different when analyzed in terms of donor parity, milk production, postparturient day and season. However, the numbers of TEs were significantly increased when the milk protein (%; P)/fat (%; F) ratio was over 0.95 and/or the milk urea nitrogen (MUN) was between 12 and 18 dl/ml. The results from ET showed no differences in pregnancy rates among Holstein heifers receiving other types, developmental stage codes and quality grades of embryos. The mean interval from ER to artificial insemination was 60.6 days. Moreover, 19 offspring that had milk recording data showed a similar milk yield performance to that of the donor cows. In conclusion, this study showed that in Holstein cows, embryos were recovered and transferred and resulted in production of viable calves. Furthermore, P/F ratio and MUN could be candidate indicators for selection of high-efficiency donor cows.