fluorescent timers: a new biophotonic tool

In standard reporter assays the basal activity of the cloned promoter often results in accumulation of both luciferase mRNA and protein. This “background” activity may be an advantage since, once measured, gives you some numbers that you may use to calculate a fold induction (you can't divide by 0!). However, the slow clearance rate of these pre-existing molecules substantially may delay and dilute the measurable response, hampering the accurate quantification of changes in cell signaling pathways. Hence, in standard assays, transient or relatively minor effects may be hidden and kinetics somewhat inaccurate: this explains why researchers prefer reporters with short half-life, and eventually decrease it with both mRNA and protein destabilizing elements (see for instance the RapidReporter Gaussia luciferase from Activemotif).

Today, another significant quality step in the race toward the 4th dimension (time), have been conquested: new fluorescent 'timers' (FTs) that gradually change colour from blue to red could allow researchers to track the age and dynamic behaviour of proteins in living cells. Previous work suggested that some red fluorescent proteins start out fluorescing blue, but then change to red as the protein is chemically modified over time. Vladislav Verkhusha and his colleagues at the Albert Einstein College of Medicine in New York mutated the red fluorescent mCherry, toward altered maturation rates from blue to red, getting three fluorescent proteins, each with a specific maturation rate. The proteins were used to track newly synthesized proteins in mammalian cells grown in culture, but maybe in future we will have a "flight recorder" inside a cell, to log different molecular events with respect to time.

Fedor V Subach, Oksana M Subach, Illia S Gundorov, Kateryna S Morozova, Kiryl D Piatkevich, Ana Maria Cuervo, Vladislav V Verkhusha (2009). Monomeric fluorescent timers that change color from blue to red report on cellular trafficking Nature Chemical Biology, 5 (2), 118-126 DOI: 10.1038/nchembio.138