Comparison Of Placental Development Between Cloned Piglets And Artificial Insemination-derived Piglets

The cloning technique, also called somatic cell nuclear transfer(SCNT), has been successfully established and gradually applied to various mammalian species. Currently,swine somatic cell cloning still has many problems. Firstly, the pig cloning efficiency is less than 1%. Secondly, more than 50% of the SCNT-derived piglets died before weaning. These problems seriously restrict the development of pig cloning technique. Fetal intrauterine growth and development are highly dependent on placental size and functions. Many studies have shown that Placental developmental defects is one of the main reasons for inhibiting the growth and development of cloned embryos. However, Correlation between placental abnormalities and developmental efficiency of cloned embryos were only reported in few mammals, there are no laboratories report about the relationship of the placenta-related traits and the postnatal survival rate of cloned piglets. Therefore, research to placental developmental status of the cloned pigs will be of great importance in improving or enhancing the pig cloning efficiency and postnatal survival rate.This study compared placenta-related traits, morphology, gene m RNA and protein expression levels between SCNT-derived and artificial insemination(AI)-derived piglets,thereby exploring the relevance between placental development and birth survival rate of the cloned piglets. The main findings are as follows:(1) The average litter size of the SCNT group was significantly lower than the AI group(4.5VS. 11.8), the stillbirth rate and the mortality of 4 days after birth in cloned piglets reached20.7% and 51.7%,respectively.(2) Comparative analysis of piglet birth weight and placenta-related traits between the cloned piglets and the AI piglets during at birth indicates that piglet birth weight, placental area,placental efficiency in S-LB group were significantly lower than A-LB group(P<0.05),placental weight was no significant difference. Comparative analysis during at 4 days after birth shows that piglet birth weight, placental weight, placental area in S-DW4 group were significantly lower than in S-SO4 group and in A-SO4 group(P<0.05), but the placental efficiency in S-SO4 group and in S-DW4 group were significantly lower than in A-SO4 group(P<0.05).(3) Correlation analysis showed that survival rate of intrapartum and postnatal 4 days of cloned piglets high significantly positively related to piglet birth weight, placental weight and placental area(P<0.01), and piglet birth weight showed a significant association with placental weight, placental area and placental efficiency(P<0.01).(4) Histomorphological analysis showed that placental development status of S-SO4 group closed to AI-derived placentas, but morphology of S-DW4 group placentas has obvious abnormalities, including an insufficient number of microvilli, trophoblast cells and other abnormalities. Umbilical cord morphological identification revealed that the abnormality rate of umbilical cord was significantly higher in S-LB group than in A-LB group(P<0.05).However, the abnormality rate of umbilical cord in S-SO4 group was significantly lower than S-DW4 group(P<0.05), and no difference between the group with A-SO4.(5) Gene m RNA expression and protein expression showed that m RNA expression of imprinted genes and non-imprinted genes in S-SO4 group placentas substantially no significant differences with A-SO4. However, the m RNA expression of these genes in S-DW4 group placentas showed significantly up-regulated or down-regulated, and protein detection analysis showed that abnormal expression of Cu-Zn SOD protein in S-DW4 group placentas,suggesting this placenta vulnerable to oxidative stress, placental gene m RNA expression and protein expression disorders resulted in morphology abnormal ly and function defects.In summary, Most of the cloned piglets died after birth is largely related to low piglet birth weight. Placental morphological abnormalities and functional defects are the primary cause of fetal intrauterine dysplasia of cloned pigs. Therefore, improving the placental developmental quality of cloned pigs may be a way to improve the porcine cloning fficiency and postnatal survival rate of cloned piglets, and cloned piglets should be given more cares and attentions to reduce their mortality.