In chicken embryos, viral vectors have been successfully used to transfer foreign genes in somatic cells. By using retroviral vectors, for example, genes involved in myocyte growth and differentiation in chicken embryos have been characterized (1 –3 ). The reason for the use of viral vectors is its high efficiency of gene transfection, particularly when stable gene expression is desired. However, if only transient gene expression is considered, several nonviral methods may be useful at present. In ovo lipofection gave spatial expression of a reporter gene in embryonic tissues of chickens (4 –6 ). In addition, two other nonviral methods may be applicable to chicken embryos in ovo. One is microparticle bombardment which has been widely used to transfect genes to tissues of a variety of animal species in vivo (7 ,9 ), and the other is electroporation (EP) by which foreign genes are transferred into cells through nanometer pores made on the cell membrane by applying electric pulses (10 ). The latter method is found to be more efficient than other nonviral methods (11 ), and has been tested in various animal tissues such as the rat brain, the mouse testis, and the chicken embryo (12 ,14 ).
