The triple T’s of biology are transformations, transfections, and transductions! In this blog we will discuss all things transductions. If you’ve ever wondered how they are different from or similar to the other Ts, we have your answers. If you know the basics but are here because you want to know the intricacies of transductions, we've got you covered there too.
What is a transduction?
Transduction is the process of transferring foreign nucleic acid into a cell by a viral agent. Transductions are similar to transfections, processes which introduce foreign nucleic acid into cells by any means, but are unique in that they require delivery to be viral-mediated. Transformations are usually bacterial in nature. All three of these methods involve DNA incorporation into the cell, but the mechanisms vary.
Why transduce?
So why use a virus to deliver nucleic acids? Sounds sort of dangerous at first suggestion! The good news is that viruses are very valuable biological tools, and with the right safety considerations, they aren't dangerous for controlled lab usage. Using viral transductions can offer benefits such as tissue-specificity, high efficiency, and can be selected to be either integrating or non-integrating. Read on to find out more!
Molecular basis of transduction
Transductions utilize the ‘normal’ mechanism of viral infiltration into a cell. The twist is that the typical genetic cargo — the viral genome — is swapped, at least partially, for a nucleic acid cargo of your choice. First, a viral vector is selected to perform the transduction with: either retrovirus, lentivirus, adenovirus, or AAV. Then, your desired DNA to be integrated can be cloned into the vector that you have selected. The nucleic acid will be flanked by viral packaging elements that will ensure the virus gets produced, and viral particles are packaged, when the vector is expressed. Once the design and construction steps are complete, it’s time to make virus!
The constructed viral vector containing the cargo of interest is then typically transfected along with viral packaging plasmids into a viral production cell line, usually HEK-293 cells. When all of these viral plasmids are expressed within the production cell line, viral particles will be produced and packaged, resulting in functional virions. These viral particles can infect other cells, but since the majority of the viral genome has been swapped for alternative genetic cargo, they can’t reproduce more functional viruses later on. These built-in safety features provide extra layers of risk management when working with viral vectors.
Typically, one day after transfection into the production cell line (depending on the virus), virus can be collected for the transduction step. Viral particles are secreted into the cellular media, making viral collection fairly easy. Producer cell media can be collected, centrifuged to remove any producer cells floating in it, and then sterile filtered to be extra sure nothing untoward gets transduced (like a rogue HEK-293 cell). This virus-containing media can then be placed on whatever cells you would like to infect with the virus. Then the viral particles do the rest! Downstream expression or integration resulting from transduction typically plateaus within a few days to a few weeks, depending on the virus, cell type, and/or desired event.
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| Figure 1: Transduction to expression process. A viral particle enters a host cell, enters the host nucleus, is transcribed into RNA, and is translated into protein. |
Is there an easier way?
In fact, there is! Addgene has a number of ready-to-use viral preps available for a variety of broadly applicable and popular viral vectors. Check out our viral selections to see if we have one that might work for your next experiment.
Using transduction vs. another method
Transfection and transduction seem to achieve similar outcomes, so why and when should you opt to make a virus instead of just zapping your cells? That really depends on two things. First, what type of cell or organism context you are targeting? Second, what is the biological outcome you want to achieve? For example, do you want the nucleic acid cargo to be integrated into the host genome? Expressed episomally long-term? Expressed short-term? Answering these questions will help guide you to the right method for your experiment.
A cool feature of viral work is that you can swap out your virus type to achieve different biological outcomes. For example, some viruses integrate into the host genome (lentivirus and retrovirus) while others are non-integrating (adenovirus and AAV) but can still express episomally long-term (AAV). If you perform a lipid-based or electrical-based transfection, most of the nucleic acid transfected will not stably integrate (unless you used a transposon system, CRISPR targeted strategy, etc.) and episomal expression will last ~2-7 days at moderate levels.
With regard to target cells or organism, some primary cells and differentiated cell types are picky when it comes to transfection/transduction methods. Some ‘difficult to transfect’ cells lines are amenable to transduction, making it a logical choice for efficiency. Where viruses really shine is when a specific cell type within a live organism is the target. Although rarely done, viral pseudotype can be altered to make the virus specific for a type or subtype of cells. This allows an organism to be injected with a virus, but enables tissue-specific targeting of that virus, which can’t be easily achieved with alternative methods.
Ready, set, transduce!
Making virus can sound daunting, but it is easier than you might think. We have protocols available to get you started and information on the specific viruses available to choose from. And remember, we have a selection of ready-made viruses as well. Transduce on!
Resources
Resources on Addgene.org
Resources on the Addgene blog
Topics: Viral Vectors, Viral Vectors 101
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