DNA Microinjection

Original paragraph

Generation of transgenic mice is possible because introduced DNA integrates into the germ line. The foreign DNA can then direct transcription in a predictable manner, and the genetic manipulation is transmitted to future generations (due to integration into the germ line), thus establishing a new and novel strain of the organism. First reported decades ago by Gordon and coworkers, the fundamental principles remain largely true to this day (Gordon and Ruddle, 1981). The procedure consists of preparation of the transgene, embryo collection, microinjection, transfer of the embryos, and identification of the transgenic offspring; these steps have been described more recently by Nagy and coworkers in great detail.(Nagy et al., 2003).

Key ideas:

• Transgenic animals are possible through DNA microinjection because introduced DNA from other species integrates into the germ line
• The foreign DNA can direct transcription in a predictable manner and the genetic manipulation is passed down to future generations
• The fundamental principles used in 1981 are still used today with no major changes
• The procedure consists of the preparation of the transgene, the embryo collection, the microinjection, the transfer of the embryos and the identification of the transgenic offspring

Source 

DeMayo, Janet L., Jie Wang, Dongcai Liang, Ruina Zhang, and Francesco J. DeMayo. "Genetically Engineered Mice by Pronuclear DNA Microinjection." N.p., n.d. Web. 15 Oct. 2014. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3459342/>.

Paraphrasing

DNA microinjection is the method used to make transgenic goats that produce spider silk. This technique successfully produces transgenic goats because introduced DNA from the spider integrates into the germs line and is passed along to every cell in the goat's body. The principles first used in 1981 are still used today with no major changes. The procedure for DNA microinjection consists of five basic protocols which are the preparation of spider transgene DNA for microinjection, embryo collection from donor goats, DNA microinjection into the goat embryos, embryo transfer into female goats and identification of transgenic goats. Figure 2 below is an illustration of the DNA microinjection itself, the third basic protocol.

Figure 2: An illustration of DNA microinjection
http://images.tutorvista.com/content/biotechnology/micro-injection-process.jpeg

In the preparation of the spider transgene DNA for microinjection, the part of the genes of the spider that codes for the production of its dragline silk is removed from one of its cells and then prepared for microinjection. In the embryo collection from the donor goats, there are two options - either to let the female egg fertilize naturally or use in vitro fertilization (IVF). For the natural process, the scientists have to find a healthy female goat and a healthy male goat. The male goat would then be allowed to fertilize the egg of the female goat naturally. Then the scientists extract what now is an embryo. For the IVF process, one healthy egg is chosen from the female goat and sperms from the male goat are placed in a petri dish. The fertilization will occur here thus forming an embryo. In the DNA microinjection, the transgene from the spider is injected into the extracted goat embryo using a needle. The process under a microscope can be seen in video 2 below.

Video 2: DNA microinjection under a microscope

https://www.youtube.com/watch?v=h-Bfc1GPWpE

In the embryo transfer to female goats, the embryo containing the spider transgene is placed back inside a womb of a female goat and is then allowed to develop normally. The female goat will eventually give birth but the phenotype of the offspring will look just like normal. Therefore, to find out whether or not the DNA microinjection was successful, scientists will have to do the genetic testing. In the identification of the transgenic goats, scientists can extract any cell from the offspring and then completely analyze the DNA to see if the spider transgene is actually there. If it is there, it means that the DNA microinjection process was successful and that they have successfully created a goat that is able to produce spider silk.