Abstract

Many mammalian species have recently been successfully cloned using somatic cells. We have produced cloned kittens by somatic cell nuclear transfer (SCNT). The cloning of mammals by SCNT requires epigenetic reprogramming of the differentiated state of donor cells. We recently observed that feline catus satellite DNA regions exhibit DNA methylation in the donor and somatic cells of a cloned cat. The cause of variation could lie in alterations occurring at different steps of the cloning procedure or incomplete reestablishment of DNA methylation patterns. This study was conducted to determine the methylation status of the feline catus satellite DNA region in the somatic cells of cloned cats and domestic normal cats by using a bisulfite sequencing method. Satellite sequences are heavily methylated in somatic cell chromosomes and are associated with dense heterochromatin where bundles of silent genes are wrapped up together. For the analysis of the cat satellite sequence, a 400-bp segment of the satellite genomic region, which has highly conserved 22 CpG sites, was amplified by PCR from bisulfite-treated genomic DNA, and the resulting PCR products were individually cloned and sequenced. For methylation analysis, genomic DNA was first isolated from somatic and placental cells of cloned and domestic normal cats. The DNA methylation status of the satellite DNA region was not significantly different among donor (using NT) cells (70.6, 77.0, and 79.1% in Donors A, B, and C, respectively), somatic cells of cloned cats (88.9, 82.2, and 85.9% in cloned A-1, 2, and 3; 78.0% in cloned B-1; 88.1, 78.9, 80.3, 83.2, 74.6, and 82.3% in cloned C-1, 2, 3, 4, 5, and 6, all respectively), and domestic cats (88.0, 81.6, and 81.8% in NC 1, 2, and 3, respectively). Also, the DNA methylation status of satellite DNA regions in the placenta was significantly different between cloned cats (80.5, 76.7, and 76.8% in cloned C-2, 5, and 7, respectively) and normal domestic cats (64.2, 66.7, and 74.9% in NC 1, 2, and 3, respectively). In conclusion, all of the somatic cells were highly methylated. The methylation status of the somatic cells was not different among groups, but that of placental cells was significantly different.