Abstract
In an attempt to produce transgenic amphibia, bacteriophage ${\lambda}-DNA$ was microinjected into fertilized eggs of Xenopus laevis, and the effect on early embryogenesis and the ultrastructural behavior of exogenous DNA were investigated. The effect of microinjected gene on embryonic development showed differences according to the concentration of injected DNA and the incubation temperature. Various concentrations of ${\lambda}-DNA$ were tested. Among those, microinjection of 1-2 ng DNA dissolved in 20 nl TE buffer was not shown to disturb normal embryonic development and was recorded the highest survivability to the late tadpole stage (Stage 43); however, injection of increased concentrations of DNA than above provoked irregular cleavages or abnormal appearances, which resulted in reduced survivability. When the injected embryos were incubated at low temperatures (e.g., $12^{\circ}C$), 54.5% of the embryos developed to Stage 43, whereas 42.4% survived when incubated at room temperature. The survivability showed also differences according to the injection site. 58.0% of the embryos developed to Stage 43 when microinjected into the vegetal pole, whereas 44.9% survived when microinjected into the animal pole. To understand the structural fate or behavior of injected DNA a combined light and electron microscopical study was applied. The nucleus-like structure was observed in the ${\lambda}$ DNA-injected embryos, which was quite a similar to the interphase nuclei of normal Xenopus laevis. The nucleus-like structure showed the typical double-layered nuclear membrane and nuclear complexes; however, it consisted of unusual structures such as furrows of nuclear envelope into the nucleoplasm.