Editing Gene expression (section)

===Localization===
{{Main|In situ hybridization|Immunofluorescence}}
[[File:Hunchback in situ.jpg|thumb|alt=Visualization of hunchback mRNA in Drosophila embryo.|In situ-hybridization of [[Drosophila]] [[embryo]]s at different developmental stages for the mRNA responsible for the expression of [[Drosophila embryogenesis#Maternal effect genes|hunchback]]. High intensity of blue color marks places with high hunchback mRNA quantity.]]

Analysis of expression is not limited to quantification; localization can also be determined. mRNA can be detected with a suitably labelled complementary mRNA strand and protein can be detected via labelled antibodies. The probed sample is then observed by microscopy to identify where the mRNA or protein is.

[[File:GFP structure.png|thumb|left|200px|alt=A ribbon diagram of green fluorescent protein resembling barrel structure.|The three-dimensional structure of [[green fluorescent protein]]. The residues in the centre of the "barrel" are responsible for production of green light after exposing to higher energetic blue light. From {{PDB|1EMA}}.]]

By replacing the gene with a new version fused to a [[green fluorescent protein]] marker or similar, expression may be directly quantified in live cells. This is done by imaging using a [[fluorescence microscope]]. It is very difficult to clone a GFP-fused protein into its native location in the genome without affecting expression levels, so this method often cannot be used to measure endogenous gene expression. It is, however, widely used to measure the expression of a gene artificially introduced into the cell, for example via an [[expression vector]]. By fusing a target protein to a fluorescent reporter, the protein's behavior, including its cellular localization and expression level, can be significantly changed.

The [[enzyme-linked immunosorbent assay]] works by using antibodies immobilised on a [[microtiter plate]] to capture proteins of interest from samples added to the well. Using a detection antibody conjugated to an enzyme or fluorophore the quantity of bound protein can be accurately measured by [[fluorometric]] or [[Colorimetry (chemical method)|colourimetric]] detection. The detection process is very similar to that of a Western blot, but by avoiding the gel steps more accurate quantification can be achieved.