Microinjecting cells using a pulsed-flow microinjection system

Generation of Infectious Mimivirus Virions Through Inoculation of Viral DNA Within Acanthamoeba castellanii Shows Involvement of Five Proteins, Essentially Uncharacterized

One of the most curious findings associated with the discovery of Acanthamoeba polyphaga mimivirus (APMV) was the presence of many proteins and RNAs within the virion. Although some hypotheses on their role in Acanthamoeba infection have been put forward, none have been validated. In this study, we directly transfected mimivirus DNA with or without additional proteinase K treatment to extracted DNA into Acanthamoeba castellanii. In this way, it was possible to generate infectious APMV virions, but only without extra proteinase K treatment of extracted DNA. The virus genomes before and after transfection were identical. We searched for the remaining DNA-associated proteins that were digested by proteinase K and could visualize at least five putative proteins. Matrix-assisted laser desorption/ionization time-of-flight and liquid chromatography–mass spectrometry comparison with protein databases allowed the identification of four hypothetical proteins—L442, L724, L829, and R387—and putative GMC-type oxidoreductase R135. We believe that L442 plays a major role in this protein–DNA interaction. In the future, expression in vectors and then diffraction of X-rays by protein crystals could help reveal the exact structure of this protein and its precise role.

Preparing injection pipettes on a PUL-1 micropipette puller

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. Needles for microinjection can either be pulled from glass capillaries on a pipette puller or be purchased premade. When pulling needles, variables such as filament design, heat, pull strength (tension), and delay time between heating and pulling must be addressed. The heat setting affects the length and the tip size of the needle; high heat will typically produce longer needles and finer tips. The pull strength will also affect length and tip size, with greater pull strength producing longer tapered needles with finer tips. Finally, shorter delay times between heating and pulling can result in longer tapers and finer needles; if the delay is too short, the glass forms fibers resembling glass wool rather than usable needles. The advantage of pulling needles in the laboratory is that a variety of different needle types can be pulled, depending on the samples and the cells being injected. The PUL-1 micropipette puller is a robust and inexpensive machine that can be found in many laboratories around the world. New machines are no longer being manufactured, although used ones can still be purchased.

DNA sample preparation and loading sample into pipettes for microinjection of cells

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. This protocol describes in general the preparation and loading of plasmid DNA for microinjections. Plasmid DNA can be purified by traditional means such as cesium chloride density ultracentrifugation, or by commercially available resin-based purification kits. The resulting preparation can then be delivered into microinjection needles either by backfilling or by a forward-filling approach.

Plating cells for microinjection

The efficient delivery of exogenous DNA to cells for expression and function studies is an essential technique of modern cell biology, and direct delivery of genetic material by microinjection remains a reliable means of transfection. This protocol describes the general procedures needed to culture cells for microinjection. Coverslips need to be marked so that microinjected cells can be identified at desired time points after injection. Coverslips can be etched by the user, as described here, or pre-etched coverslips can be purchased. Once the coverslips have been etched and sterilized, cells can be plated onto them and allowed to grow.