A fundamental aspect of biological research is the introduction of foreign material into a cell to modify its genetic composition. This process is known as transformation. It can be accomplished by several physical techniques, such as microinjection and electroporation, or chemically by gene bombardment. The goal of any transformation experiment is to transfer foreign DNA into the nucleus of a host cell. Until recently, these approaches were expensive, slow, and required skilled personnel. Newer technology is making them more reliable, repeatable and affordable.
Microinjection uses a glass micropipette or metal microinjection needle to inject genetic material directly into a living cell or embryo. It is most often used to transfer DNA into a fertilized egg to create a transgenic organism.
It is also a useful technique for introducing RNA into cells. It is a useful tool for establishing cellular models and a means of studying the function of intracellular structures such as mitochondria and nuclear envelopes (Mello et al, 1991; Evans & Mello, 1995). The procedure can be used to introduce both small and large quantities of plasmid DNA into cells.
This method of introducing foreign DNA into cells has been a major tool in the development of transgenic mice and other organisms. It is commonly used for introducing foreign DNA into the nucleus of an egg, which is then transferred to a pseudopregnant female mouse so that it can fuse with the fertilized oocyte to form a transgenic embryo. This procedure is known as pronuclear injection or DNA microinjection (Fig. 8.8A). In most cases, only a percentage of injected eggs will survive the process. Some will arrest at the one-cell stage, while others will develop incorrectly and show a fragmented appearance (Fig. 8.8B).
A major challenge in the microinjection of cells, oocytes and embryos is to deliver a precise volume of injection material. This challenge has been addressed with the development of a new quantitatively controlled microinjection technique. This system combines a pre-patterned cell trapping chip with an automated microinjection pipette. The precise amount of material injected into cells or oocytes is measured by volumetric changes in water droplets dispensed in mineral oil and injected with a fluorescent dye under calibrated injection pressures and times.
Designed to simplify the task of injecting fluid elements at the microscopic level, our line of PV820 and PV530 Pneumatic PicoPumps provides users with a high-performance platform that delivers repeatable injections in volumes from picoliters to nanoliters. This powerful pump features a convenient touch screen control and footswitch operation, and it takes up little space on the lab bench. Its hold pressure guards against injectant dilution through capillary action by keeping the injectant meniscus at the tip of the pipette.
Nikon offers a range of microscopes that are compatible with microinjection work, including the ECLIPSE Ti2 and ECLIPSE Ts2R series inverted microscopes and SMZ18/25 stereomicroscopes. All of these systems are designed to withstand the vibrations and temperature fluctuations that can occur during microinjection experiments, helping to maintain the integrity of the sample. micro injection