**1. Introduction**

696 Biomedical Science, Engineering and Technology

Zhong, X., Li, N., Liang, S., Huang, Q., Coukos, G. & Zhang, L. (2010). Identification of

Zhu, X., Pan, X., Wang, W., Chen, Q., Pang, R., Cai, X., Hoffman, A. & Hu, J. (2010).

cells. *Biomaterials,* Vol.31, No.10, (April 2010), pp. 2779-2787, ISSN 1878-5905

41961-41971, ISSN 1083-351X

mircoRNAs regulating reprogramming factor Lin28 in embryonic stem cells and cancer cells. *Journal of Biological Chemistry,* Vol.285, No.53, (December 2010), pp.

Transient in vitro epigenetic reprogramming of skin fibroblasts into multipotent

Transgenic technology has been applied mainly in the study of gene structure and function in model organisms and gene therapy for human diseases. Transgenic technology has potential for rapidly improving quantity and quality of agricultural products, compared to traditional selection and breeding methods in domestic animals that are time consuming when attempting to alter the desired allele frequency for specific traits. Additionally, transgenic animals can be used as biomedical research models or directly for human health, by producing recombinant pharmaceutical proteins and/or organs for xenotransplantation. Due to the advantage of bypassing the need of embryonic stem (ES) cells that are difficult to isolate in domestic animal species, cell-based method of transgenesis followed by somatic cell nuclear transfer (SCNT) is currently widely applied. However, due to the limitations in making genetic modifications and SCNT, producing genetically modified animals is still inefficient. Fortunately, the current advancement of new techniques and methods in both gene targeting (Urnov et al., 2010) and abilities to produce pluripotent stem cells (Voigt and Serikawa, 2009) holds great promises for this field.

In this chapter, we will review the recent progress and technical route of the cell-based method of transgenesis by SCNT and discuss the newly emerging methods to enrich the gene targeting frequency of somatic cells. We will also discuss factors to improve the efficiency of SCNT and our future perspectives on the promises of this field.
