Proof of concept

Five different plasmids were assembled with the Plug ‘n’ Play standard in order to verify that the system functions in mammalian cells. To demonstrate how fast any vector of choice for the expression in mammalian cells can be assembled, we designed a reporter system as proof of concept.

The plasmids for proof of concept in mammalian cells were constructed with the strong constitutive cytomegalovirus (CMV) promotor, the BGH terminator, the hygromycin marker cassette, and the plasmid backbone, BBa_K678023. Different genes encoding fluorescent proteins were used as the gene of interest, and the reporter system can easily be modified to be used for gene expression analysis. All transient transfections were performed in the human derived cell line U-2 OS, kindly provided by the Danish Cancer Society. For microscopy the transfected U-2 OS cells were fixed using 4% formaldehyde, and VECTASHIELD was added to prevent rapid loss of fluorescence while examining the cells with the confocal microscope.

We have proved that the Plug ‘n’ Play assembly standard can easily be applied for construction of mammalian expression vectors. Transfection and expression of the fluorescent proteins GFP, mCherry, YFP, and CFP were successfully conducted in U-2 OS. Furthermore, expression of GFP targeted to the peroxisomes of U-2 OS cells succeeded. It was also shown that mammalian cells can be transfected with different fluorescent proteins simultaneously.

This reporter system could developed further developed enabling the localization of proteins to specific organelles. Such a system would allow the study of organelles and other compartments in real time.

pJEJAM1 BBa_K678049

pJEJAM1 is a plasmid intended for transient transfection of mammalian cells. The expression of the green fluorescence protein (GFP) is under the control of the strong constitutive CMV promoter, which can be seen in the figure below.

U-2 OS cells transiently transfected with pJEJAM1 expressing GFP. This plasmid provides a good expression and homogenous distribution of GFP. The white bar has a length of 20μm.	U-2 OS cells transiently transfected with pJEJAM1 expressing GFP. This vector provides a good expression and homogenous distribution of GFP. The white bar has a length of 20μm.

pJEJAM2 BBa_K678050

pJEJAM2 is a plasmid intended for transient transfection of mammalian cells. The expression of GFP is under the control of the strong constitutive CMV promoter (see the figure below). The peroxisomal targeting signal PTS1 is directly fused to the C-terminal of GFP, this sequence should ensure the localization of GFP to the peroxisomes of the cell. Although the microscopy shows GFP distributed in points, further analysis are necessary to confirm that GFP is in fact is targeted to the peroxisomes.

U-2 OS cells transiently transfected with pJEJAM2 expressing GFP localized to the peroxisomes. As can be seen on the picture this vector most likely localizes GFP to the peroxisomes of the cells. The white bar has a length of 30μm.

pJEJAM3 BBa_K678051

pJEJAM3 is a plasmid intended for transient transfection of mammalian cells. The expression of the yellow fluorescence protein (YFP), is under the control of the strong constitutive CMV promoter (see the figure below).

U-2 OS cells transiently transfected with pJEJAM4 expressing YFP. This vector provides a good expression and homogenous distribution of YFP. The white bar has a length of 40μm.	U-2 OS cells transiently transfected with pJEJAM4 expressing YFP. This vector provides a good expression and homogenous distribution of YFP. The white bar has a length of 30μm.

pJEJAM4 BBa_K678052

BBa_K678052 is a plasmid intended for transient transfection of mammalian cells. The expression of mCherry, a red fluorescence protein, is under the control of the strong constitutive CMV promoter (see the figure below).

U-2 OS cells transiently transfected with plasmid BBa_K678052 expressing mCherry. This vector provides a good expression and homogenous distribution of mCherry. The white bar has a length of 70μm.	U-2 OS cells transiently transfected with plasmid BBa_K678052 expressing mCherry. This vector provides a good expression and homogenous distribution of mCherry. The white bar has a length of 50μm.

pJEJAM5 BBa_K678053

BBa_K678053 is a plasmid intended for transient transfection of mammalian cells. The expression of cyan fluorescence protein (CFP), is under the control of the strong constitutive CMV promoter (see the figure below).

U-2 OS cells transiently transfected with plasmid BBa_K678053 expressing CFP. This vector provides a good expression and homogenous distribution of CFP. The white bar has a length of 70μm.	U-2 OS cells transiently transfected with plasmid pJEJAM5 expressing CFP. This vector provides a good expression and homogenous distribution of CFP. The white bar has a length of 50μm.

Mix'n'Play

Mammalian cells can be transiently transfected with several plasmids at once, allowing the simultaneous expression of different fluorescence proteins. The pictures below demonstrate different combinations of fluorescent proteins.

U-2 OS cells transiently transfected with plasmids BBa_K678050 and BBa_K678053 expressing GFP localized to the peroxisomes and CFP. The white bar has a length of 30μm.	U-2 OS cells transiently transfected with plasmids BBa_K678049 and BBa_K678053 expressing GFP and CFP. The white bar has a length of 30μm.
U-2 OS cells transiently transfected with plasmids BBa_K678049 and BBa_K678052 expressing GFP and mCherry. The white bar has a length of 70μm.	U-2 OS cells transiently transfected with plasmids BBa_K678052 and BBa_K678053 expressing YFP and CFP. The white bar has a length of 40μm.