Yes! Researchers at McGill University engineered a type of cell much like this one, where GFP level provided a readout of gene activity.
Researchers placed the GFP gene into cells growing in culture dishes. Then they added different compounds to the cells. They compared the amount of GFP that the cells produced before and after they added the compounds to see whether they made the gene more or less active.
A compound called AdoMet, a source of methyl tags, decreased GFP output. Valproic acid, an anti-epilepsy drug and mood stabilizer, increased GFP output. The researchers analyzed the GFP genes from these cells and confirmed that the compounds changed the number of methyl tags attached to the DNA.
Cells like this, along with other biological tools, help researchers understand how signals from the environment shape the epigenome.
In these cells, GFP production is a readout of gene activity.