Gene expression
Expressing a gene means the product that the gene encodes (usually a protein)
is made. Not all genes are expressed in every cell all the time. Genes are expressed
only when they are needed for the cell to function. By studying when or where
a gene is expressed we can get some clues about its function. Gene expression
can involve the processing of a signal from outside the cell via the signal
transduction pathway and the binding of transcription
factors to DNA to cause transcription
to begin.
Important questions concerning gene expression:
- Where is the gene expressed? In what cells? In what tissues?
- When is the gene expressed? At what stage of development? During what part
of the cell cycle?
- Is there a specific stimulus that turns on expression of a gene? Growth
factors? DNA damaging agents?
- What proteins (transcription factors) regulate expression of the gene?
- Misexpression (overexpressing or expressing at an incorrect time) can produce a phenotype that tells us about the function. For example, an overexpressed oncogene may cause a normal cell to divide at inappropriate times.
Expression can be detected by:
- presence of RNA as measured by hybridization to a DNA probe containing
base pairs complementary to the RNA.
- expression of a reporter gene fused to your gene. The reporter gene is easily detected (usually by color reaction) in cells or in a tissue.
