| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 97 === In mammals, genome-wide epigenetic reprogramming systems exist in primordial germ cells and zygote. It plays a crucial role in regulating genome functions at critical stages of embryo development and confers stability of gene expression during mammalian development. Inappropriate reprogramming of donor nuclei in somatic cell resulted in neonatal death and preimplantation defects during animal cloning technique. Specific demethylation events in differentiated tissues could then lead to further changes in gene expression as needed. In this study, six cloned bovines created by ear fibroblast nuclear transfer with short life span and multiple organ defects were used as the experimental materials. We focus on three imprinting genes included two growth factor genes IGF-2, H19 and Xist (X chromosome inactive regulated gene) by combined bisulfite and restriction assay (COBRA). Bisulfite sequencing were also applied to analyze the aberrant CpG sites in different imprinted genes loci in these cloned bovine genomes. Our data show that loss of imprinting (LOI) phenomenon was frequently appeared in IGF-2, Xist and H19 imprinted loci in several tissues of these cloned bovines. Furthermore, we detected the cloned bovine NTG-2 expression of these imprinting genes with quantitative real time PCR (Q-PCR). The data suggested that IGF-2 and H19 are extremely overexpressed in liver, vein, ear, skin and uterus. The IGF-2 mRNA expression in uterus and liver of NTG-2 cow are almost 1,200 and 800 folds compared to WT cow. The H19 expression level in liver of NTG-2 also exhibited a 34,000-fold higher than that of WT cow. According to our research, the extensively overexpression of IGF-2 and H19, probably were the major reason to cause the cloned bovine NTG-2 not only organ defects, but also aberrant embryonic development. In conclusion, the death of clones may be due to aberrant DNA methylation at the loci of imprinting genes and disruption of incompletely reprogrammed after nuclear transfer.
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