A retrospective analysis of sheep generated by somatic cell nuclear transfer

• Published in: Theriogenology Vol. 227; pp. 102 - 111
• Main Authors: Liu, Ying, Stott, Rusty, Regouski, Misha, Fan, Zhiqiang, Perisse, Iuri Viotti, Patrick, Tayler, Keim, Jacob, Meng, Qinggang, Polejaeva, Irina A.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.10.2024
• Subjects: Adult and prepubertal oocytes; Animals; Cloning, Organism - methods; Cloning, Organism - veterinary; Embryo Culture Techniques - veterinary; Embryo Transfer - methods; Embryo Transfer - veterinary; Female; Nuclear transfer; Nuclear Transfer Techniques - veterinary; Oocytes - physiology; Pregnancy; Retrospective Studies; Sheep; Sheep - embryology; Pregnancy; Nuclear transfer; Sheep; Adult and prepubertal oocytes
• ISSN: 0093-691X; 1879-3231; 1879-3231
• DOI: 10.1016/j.theriogenology.2024.07.017

Somatic cell nuclear transfer (SCNT) is one of the primary methods for production of genetically engineered sheep, which allows for gene editing or transgene introduction in somatic cells. The use of SCNT eliminates the risk of genetic mosaicism in embryos and animals that is commonly observed after zygote micromanipulations. This retrospective analysis of SCNT in sheep performed at Utah State University, spanning from 2016 to 2021, examined parameters that may impact pregnancy and full-term development, including donor oocytes (donor age), donor cell lines, SCNT parameters (time of oocyte activation following SCNT, number of transferred embryos, in vitro maturation and culture conditions), and recipients (surgical number and ovulatory status), as well as factors that may correlate with large offspring syndrome or abnormal offspring syndrome (LOS/AOS) in the fetuses and lambs. Our findings indicated that compared to prepubertal oocytes, the SCNT embryos produced from adult sheep oocytes had comparable in vitro maturation rates, pregnancy and full-term development rates, as well as SCNT efficiency. In addition, earlier activation time of SCNT embryos (e.g. 24–26 h post maturation) was correlated to the early pregnancy loss rate, full-term rate, and SCNT efficiency. Compared to our standard serum-containing medium, commercial serum-free culture medium showed a positive correlation with the full-term development of sheep SCNT embryos. Transferring 15–30 embryos per recipient resulted in consistently good pregnancy rates. Surgical numbers and ovulatory status (having at least one follicle between 6 and 12 mm in size or a corpus hemorrhagicum (CH)) of recipients did not affect pregnancy and full-term development rates. In summary, this retrospective analysis identified parameters for improving pregnancy and full-term development of SCNT embryos in sheep. •The age of oocyte donors does not affect pregnancy rate of SCNT embryos, and SCNT efficiency.•Earlier activation time of SCNT embryos is correlated to the higher SCNT efficiency in sheep.•Surgical number and ovulatory status of recipients would not affect pregnancy and full-term development rates.