Key Difference – Selectable Marker vs Reporter Gene
Genetic engineering technique is used to transfer important genes from organism to another organism. Insertion of a foreign gene into another organism’s genome and making it expressed within the host cell are most difficult steps in gene transferring. To detect the success of the transformation process, a selectable marker and a reporter gene are used in the recombinant molecule. A selectable marker is a DNA sequence or a gene which expresses and selects the transformed cells from the non-transformed cells. A reporter gene is another gene which is used to distinguish transformed cells and to quantify or detect how the inserted gene functions within the host. The key difference between selectable marker and reporter gene is that the selectable marker is used to screen out the non-transformed cells and to signal the transformed cells while reporter gene is used to quantify the level of gene expression within the host.
CONTENTS
1. Overview and Key Difference
2. What is Selectable Marker
3. What is Reporter Gene
4. Side by Side Comparison – Selectable Marker vs Reporter Gene
5. Summary
What is a Selectable Marker?
In genetic engineering, the gene of interest is inserted into a suitable vector and transformed into host organisms. However, the transformation is successful only in the competent host cells, and there is a possibility of host cells to reject the uptake of foreign DNA. Therefore, differentiation of the transformed and non-transformed cells is important to continue with further experimentation. Hence, researchers incorporate a selectable marker gene to vector for easy selection of the transformed cells from non-transformed cells. A selectable marker is a DNA sequence, especially a gene useful in identification of the transformed cells. This marker gene exhibits a trait which suits an artificial selection of transformed cells from non-transformed cells on a media.
Most common selectable markers used in molecular biology are antibiotic resistant genes. An antibiotic resistance gene is inserted into the vector and transformed into host cells especially to the host bacterium. That particular antibiotic is incorporated into the growing medium of the bacterium. Due to the presence of the selective marker, under the selective conditions, only cells that contain the appropriate selectable marker can survive. Non-transformed cells are unable to grow in the antibiotic-containing medium. Therefore, due to the selectable marker which is antibiotic resistant, transformed cells are easily identified.
Genes that confer traits for antimetabolites, herbicides are used as selective markers in cloning vectors in plant genetic engineering. However, this cotransformation of selective markers into genetically modified organisms has negative effects on the environment and human. The release of antibiotic resistant bacteria can increase the antibiotic resistivity of human pathogens. It can contaminate the product or biomass by antibiotics and can lose the selective pressure as a result of antibiotics degradation and inactivation.
Figure 01: Plasmid vector for gene transfer with selectable marker
What is a Reporter Gene?
Reporter genes are genes that enable the detection or measurement of the inserted gene expression. These reporter genes can be attached to regulatory sequences of the gene of interest to signal the expression location or levels. Therefore, during the expression of genes under the same promoter, they are transcribed into a single mRNA sequence and then translated into a protein which can indicate the level of gene expression.
Reporter genes are of various types, and they contain visually identifiable characteristics which are usually involved in fluorescent and luminescent proteins. Genes that code fluorescent protein and enzymes, convert invisible substrates to luminescent or coloured products by signaling the successful gene expression and giving the opportunity for quantification of the gene expression.
Figure 02: Reporter Gene Expression
What is the difference between Selectable Marker and Reporter Gene?
Selectable Marker vs Reporter Gene |
|
| Selectable marker is a kind of DNA sequence which helps to distinguish transformed cells with non-transformed cells. | Reporter gene is a gene which helps to quantify the expression of the desired gene inserted into the host cell. |
| Nature of the Units Produced | |
| Genes are encoded with characteristics which help in artificial selection on growing media. | Genes are encoded with visually identifiable characteristics. |
| Usage | |
| Antibiotic resistance genes, antimetabolite genes, herbicide resistance genes, etc. are examples for selectable marker. | Genes code for green fluorescent protein, β-glucuronidase, Chloramphenicol acetyltransferase, Red fluorescent protein, etc. are examples. |
Summary – Selectable Marker vs Reporter Gene
Selectable markers allow transformed cells to grow in selective media dosed with particular antibiotic or herbicide. They are used for early selection of transformed cells. Reporter genes are used to quantify the level of expression of the desired gene inserted. They also allow the differentiation of transformed and non-transformed cells. This is the difference between selectable marker and reporter gene. Both selectable marker and reporter gene are considered as important markers in genetic engineering.
References:
1. Ziemienowicz, Alicja. “Plant selectable markers and reporter genes.”SpringerLink. Springer-Verlag, n.d. Web. 23 Mar. 2017.
2. Shih, Chen-Han, Hsiao-Yin Chen, Hung-Chieh Lee, and Huai-Jen Tsai. “Purple Chromoprotein Gene Serves as a New Selection Marker for Transgenesis of the Microalga Nannochloropsis oculata.” PLOS ONE. Public Library of Science, n.d. Web. 25 Mar. 2017
Image Courtesy:
1. “Plasmid with insert” By Michael Jeltsch – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Reporter gene” By TransControl at en.wikipedia (CC BY-SA 3.0) via Commons Wikimedia