Cell Specific Gene Expression

Every cell in the body of a multicellular organism possesses the same DNA; however, different cell types have notable structural and functional differences which can be attributed to the differential expression of genes in the cell. 

Additionally, specific cells express different genes over time due to changes in the cell or organism. The variety of RNA and proteins produced enables cells to carry out their unique functions at the appropriate times.

Liver cells, called hepatocytes, express a different set of genes compared to neurons.

For example, liver cells produce alcohol dehydrogenase, an enzyme that breaks down toxic alcohols into acetaldehyde, which then can further be metabolized to produce carbon dioxide and water.  

In contrast, neurons produce neurexins, a group of proteins in the brain that helps transmit information from one neuron to an adjacent one. 

Cells have mechanisms to control gene expression at multiple regulatory steps before, during, and after transcription and translation. However, transcriptional regulators are common because it prevents the synthesis of mRNA transcripts.  

During liver development in humans, the transcription factors C/EBP α, C/EBP β, and Hepatocyte Nuclear Factor-1 contribute to the liver-specific expression of alcohol dehydrogenase genes. 

Gene expression is also regulated in response to the extracellular environment.  

When blood glucose levels decrease, the pancreas secretes the hormone glucagon.  When exposed to glucagon, liver cells express phosphoenolpyruvate carboxykinase, a protein required for the production of glucose from non-carbohydrate precursors.