We, the iGEM Team Freiburg 2014, have the goal to combine the capability of viral vectors for stable gene transfer with the spatio-temporal resolution of optogenetics for gene delivery into mammalian cells. We utilized the Murine Leukemia Virus (MuLV) that specifically uses the murine mCAT-1 receptor to infect target cells. By using a blue light inducible expression system, we brought the receptor to the plasma membrane of illuminated cells to enable targeted gene delivery by the virus.

Our project was quite a large success! We:

• produced MuLV viruses containing different reporter proteins,
• optimized MuLV production and transduction protocols to reach close to 100% efficiency,
• created stable mammalian cell lines using the MuLV virus,
• generated patterns of reporter proteins in cell cultures by light exposure,
• demonstrated that the virus exclusively infects cells expressing the mCAT-1 receptor,
• infected cells with the MuLV virus that expressed the mCAT-1 receptor after light induction.

We provide the virus as a tool for the generation of stable mammalian cell lines under biosafety level 1 regulations. Our viral vector, which we propose as a new iGEM RFC, enables the user to introduce any gene of interest stably into mammalian cell lines. Therefore we provide for the iGEM community a fast, easy to handle and safe way of generating stable cell lines.

During the course of iGEM, we learned many new techniques:

• mammalian cell culture,
• fluorescence activated cell sorting,
• virus production under biosafety level 1 and biosafety level 2 conditions,
• many different cloning techniques,
• widefield and confocal microscopy,
• creating a website,

and, last but not least, we had a lot of fun and learned how to work together as a team!