37 Healthy Foals Produced Using Bone Marrow-Mesenchymal Stem Cells as Nuclear Donors in Horse Cloning

Somatic cell nuclear transfer efficiency is based on the capacity of the donor cell to be reset and reprogrammed to an embryonic state. So, the less differentiated the donor cells are, the more easily they could be reprogrammed by a recipient cytoplasm. Failures on appropriate nuclear reprogramming frequently lead to abnormalities associated with the placenta, umbilical cord, birthweight, and limbs. In the present study, we evaluated the efficiency of bone marrow mesenchymal stem cells (BM-MSC) compared with adult fibroblasts (AF) as nuclear donors in horse cloning and evaluated both in vitro and in vivo development of the embryos generated. Moreover, we focused on comparing the health of the foals generated and on the presence of anatomical abnormalities in foals produced from the different treatments. Embryos produced by AI, recovered by uterine flushing, and transferred to recipient mares were used as controls. All variables were analysed by Fisher test (P < 0.05). The cloning procedure was performed according to Olivera et al. (2016 PLoS One 11, e0164049, 10.1371/journal.pone.0164049). Both cleavage and blastocyst rates were higher when MSC were used as nuclear donors (P < 0.05). Cleavage rates were 85.6% (3875/4527) v. 90.2% (3095/3432) and blastocyst rates were 10.9% (492/4527) and 18.1% (622/3432) for AF and MSC groups, respectively. In the AF group, 476 blastocysts were transferred to recipient mares (232 transfers), and in the MSC group, 594 blastocysts were transferred 297 transfers). In the AI control group, 88 embryos were transferred. Pregnancies were diagnosed by transrectal ultrasonography 15 days after embryo transfer in all the groups. Pregnancy rates were similar between both cloning groups (41/232, 17.7% and 37/297, 12.5%for AF and MSC, respectively), but higher in the AI group (71/88, 80.7%). However, significant differences were observed in the birth of viable offsprings among the cloning groups. Despite similar rates of foal delivery (AF, 17/41, 41.5%; MSC, 21/37, 56.7%), a higher proportion of viable foals were obtained from the MSC group (20/37, 54.1%) compared with the AF group (9/41, 22%; P < 0.05). Surprisingly, as in the AI group (63/63, 100%), all of the viable foals obtained using MSC (20/20, 100%) were considered normal and did not show abnormalities associated with cloning. In contrast, in the AF group, only 4/9 (44.4%) were considered normal foals. The defects present in the other 5 foals were related to flexural and angular limb deformities and umbilical cord malformations. These were corrected rapidly with standard treatments or, in the case of the umbilical cords, minor surgery. This study shows for the first time that BM-MSC can be used as nuclear donors in horse cloning and that the foals obtained are as healthy as those produced by AI, showing no abnormalities related to deficiencies in nuclear reprogramming.