Hosting A Genetic Circuit

Synthetic biologists refer to the host cells for their ‘genetic circuits’, inserted genes sequences, as a ‘chassis’. You can think of the genetic circuit as computer code, and the chassis as the machine that will run it. The chassis manages all the material a genetic circuit requires to function, providing building blocks for protein synthesis, energy and an environment in which the inserted genes can operate. Cellular machinery is essential for reading a circuit's information. Synthetic biologists generally use a small suite of well understood chassis, primarily Escherichia coli (E.coli), in order to better standardise their creations and allow for the easy use of parts in labs worldwide. Other cell types must often be used for different types of circuit. The properties of a chassis often need to complement the properties of its genetic circuit. Highly specialist chassis may have to be used to perform specific tasks.

If a chassis is to be a cell from a multicellular organism, then they can either be taken from that organism directly and used, these are primary cells and are generally harder to transfect, or immortalised cell lines are used. Immortalised cell lines can survive for long periods of time in vitro because, while they cannot divide indefinitely, they have been genetically manipulated to sidestep cellular senescence. Their behaviour is generally a good approximation to cells of the same type working in an organism, but the mutations and their accumulated genetic alterations can change their functioning slightly.


In our project, we used three different chassis; E.coli, HeLa cells and microglial cells. E.Coli are used to create our BioBricks, since they are easy to work with and have a high proliferation rate. They can produce relatively large amounts of recombinant plasmid in a short time frame.


Owing to difficulties obtaining microglia and the fact that, as immune cells, they are harder to transfect, we began work in HeLa cells to characterise our BioBricks and show that they work in a human cell line. HeLa cells are an immortalised human cell line of cervical cells derived from a cancer patient, Henrietta Lacks, who died of her illness in 1951. Given the appropriate growth medium and space, HeLa cells are capable of dividing rapidly and for a mammalian cell line are incredibly persistent - so much so that we have to be careful that we do not give them the opportunity to infect other cell lines in our mammalian lab. Because HeLa cells are cancerous, they produce more telomerase to overcome the Hayflick limit. Ethical debate surrounds the wide use of these cells because the Lacks family never gave full consent for their use in science and the identity of their source become widely known. They are, however, a human cell standard, and easily assimilated into iGEM's ethic of standardisation. They are relatively hardy and easy to transfect.


We intend to the immortalised human microglia SV-40 cell line. However, at the time of wiki freeze, despite ordering these cells in August, we have not received them. Arriving late from Applied Biological Materials and subsequently stuck in UCL's bureaucratic machinery that surrounds the lab (since they are human tissue cells) we nevertheless expect to be able to work with them after the jamboree and fully intend to continue to create our circuit in them whatever our results in the iGEM competition.