BACKGROUND: Green Fluorescent Protein (GFP) is used extensively as a reporter 
for transgene expression in Drosophila and other organisms. However, GFP has not 
generally been used as a reporter for circadian patterns of gene expression, and 
it has not previously been possible to correlate patterns of reporter expression 
with 3D movement and behavior of transgenic animals.
RESULTS: We present a video tracking system that allows tissue-specific GFP 
expression to be quantified and correlated with 3D animal movement in real time. 
eyeless/Pax6 reporter expression had a 12 hr period that correlated with fly 
activity levels. hsp70 and hsp22 gene reporters were induced during fly aging in 
circadian patterns (24 hr and 18 hr periods, respectively), and spiked in the 
hours preceding and overlapping the death of the animal. The phase of hsp gene 
reporter expression relative to fly activity levels was different for each fly, 
and remained the same throughout the life span.
CONCLUSION: These experiments demonstrate that GFP can readily be used to assay 
longitudinally fly movement and tissue-specific patterns of gene expression. The 
hsp22-GFP and hsp70-GFP expression patterns were found to reflect accurately the 
endogenous gene expression patterns, including induction during aging and 
circadian periodicity. The combination of these new tracking methods with the 
hsp-GFP reporters revealed additional information, including a spike in hsp22 
and hsp70 reporter expression preceding death, and an intriguing fly-to-fly 
variability in the phase of hsp70 and hsp22 reporter expression patterns. These 
methods allow specific temporal patterns of gene expression to be correlated 
with temporal patterns of animal activity, behavior and mortality.