Transgenic animals have been used to study gene function, produce important proteins, xenotransplantation donor, and generate models for the study of human diseases. Recent progress in animal cloning has provided an attractive alternative to improve transgenic efficiency, through the combination of transfection and somatic cell nuclear transfer (SCNT). However, when transgenic animals are produced by SCNT using randomly transfected cells as donor, the integration sites of transgene cannot be predicted. Many methods on the basis of genome walking have been demonstrated to clone transgene integration sites but they are either complicated or inefficient. In the study, we report a PCR-based method, thermal asymmetric interlaced PCR (TAIL-PCR), which relies on a series of 3 nested PCR reactions with transgene specific, designed with melting temperature of about 64, and arbitrary degenerate primers, by control of annealing temperature to efficiently reduce the nonspecific amplification to clone the integration sites in transgenic pigs by SCNT. Junction PCR combined with transgene-specific and integration site primers was performed to confirm the integration sites. Three integration sites were found (1 mapped on chromosome 4; the other 2 met a significant match in the pig expressed sequence tag database) in 2 founder transgenic pigs. Junction PCR resulted in specific amplification bands to identify the integration sites, and segregation of the integration sites was also detected in subsequent progeny by junction PCR analysis. We also used junction PCR combining with transgene-specific 5′ and 3′ integration site primers to analyze zygosity of the integration sites. Besides the specific amplification bands amplifying by transgene specific and integration site primers, bands amplified by 5′ and 3′ integration site primers were obtained to determine the heterozygosity of integration site. In conclusion, this strategy can be efficiently employed to clone transgene integration site and determine zygosity.
This work was supported by grant from the State Transgenic Research Programme of China (Grant No. 2008ZX08006-002).
RAISING: a high-performance method for identifying random transgene integration sites
