CH391L/S12/Selectablegeneticmarkers

Selectable Markers Overview

Example application of selectable genetic markers in nematodes. Only nematodes transfected with markers survive and proliferate[1].

Selectable genetic markers are exogenous genes that are introduced into a cell, conferring a previously absent resistance. These markers are primarily used to "mark" the successful transformation of DNA into a plasmid. Oftentimes, selectable markers are accompanied by other exogenous genes that is the primary gene of interest; the marker simply serves to distinguish between successful transformations, and unaltered cells. It is not atypical to witness transformation efficiencies as low as .05%, making it difficult to pick correct cellular colonies without additional techniques.

This is where the selectable genetic markers prove their usefulness. For instance, selectable genetic markers can be used to confer ampicillin resistance to E. coli. These newly resistant E. coli can then be grown on culture plates with ampicillin, allowing only E.coli with successfully transformed DNA to proliferate.

In addition to selectable genetic markers are screenable genetic markers. Screenable genetic markers function in a similar manner in that they are extraneous genes that are transformed into a cell; however, they do not confer any new sort of resistance to the cell. Instead, they cause the cell to respond differently to environmental conditions in such a way as to distinguish transformed cells from untransformed cells. This can be useful when determining the transformation efficiency of a cell, or when carefully monitoring the activity of proteins.

Screening

Green Fluorescent Protein

Mice transfected with GFP. One can easily distinguish the wild-type mouse (middle) from the two mice with GFP (left and right)[2].

Green Fluorescent Protein, or GFP, was first isolated from the crystal jellyfish Aequorea victoria in the 1960s. In 1994, GFP was successfully cloned[3], allowing researchers to use the protein as a screenable marker for the first time. Virtually harmless in live cells, GFP has the unique pheotype of glowing bright green under ultraviolet light. GFP functions entirely of its own accord, and requires no exogenous material besides ionizing radiation in order to fluoresce. This allows GFP to be used as a marker accompanying transfected DNA, and has been used extensively in academia.

In 2011,

References

1. Giordano-Santini R and Dupuy D. Selectable genetic markers for nematode transgenesis. Cell Mol Life Sci. 2011 Jun;68(11):1917-27. DOI:10.1007/s00018-011-0670-1 |

   Review article about selectable genetic markers as used in nematodes. Relatively new field for nematodes, possible due to the completion of the Caenorhabditis elegans genome.

2. Moen I, Jevne C, Wang J, Kalland KH, Chekenya M, Akslen LA, Sleire L, Enger PØ, Reed RK, Øyan AM, and Stuhr LE. Gene expression in tumor cells and stroma in dsRed 4T1 tumors in eGFP-expressing mice with and without enhanced oxygenation. BMC Cancer. 2012 Jan 17;12:21. DOI:10.1186/1471-2407-12-21 |

   Observes tumor growth in mice by introducing GFP into the mice.

3. Chalfie M, Tu Y, Euskirchen G, Ward WW, and Prasher DC. Green fluorescent protein as a marker for gene expression. Science. 1994 Feb 11;263(5148):802-5. DOI:10.1126/science.8303295 |

   The first instance of using GFP as a marker.