Transgenic fusions between a gene and a reporter are used to determine whether a gene is expressed. ...

The reporter genes are extremely helpful for tracking gene expression, but it is important that the reporter product does not harm the organism. For instance, lacZ is often used to screen cells in culture through blue-white screening, but requires the substrate X-gal to produce the blue product. Injecting X-gal into a living organism may have toxic effects and is, therefore, not commonly used when researchers want to examine living organisms. Alternatively, reporter genes such as green fluorescent protein (GFP) are not toxic and require no substrate. They have been
used as markers in the cloning of transgenic pigs and have had no toxic effects. The other concern
is the effect of the reporter gene fusion on wild-type function of the protein. Because protein conformation and proper folding of the protein is so important to the function of the protein, fusing another gene product to the protein can have unintended consequences for protein function. It may be necessary to test N-terminal versus C-terminal fusions, as well as using protein reporters that are different sizes. Additionally, some organisms and microenvironments may not be conducive to certain reporter genes. Fluorescent protein reporters such as GFP are not.