Using multiphoton fluorescence microscopy, a technique pioneered at Cornell by physicist Watt W. Webb, researchers have for the first time been able to watch chromosomes change their form in order to activate their genes to synthesize key proteins in fruit fly cells. The advance could be a significant step toward understanding the basic processes that underlie gene expression.
Yao used multiphoton microscopy (MPM) to image living salivary gland tissue of Drosophila (fruit flies). Unlike other methods, which lack penetrating power and can damage the specimen, MPM delivers crisp, clear images, even in thicker tissue samples like Drosophila salivary glands.
The research was ultimately possible thanks to the unique composition of the fruit flies' polytene cells -- giant, multistranded chromosomes with hundreds of sets of the genome instead of the usual two sets in conventional cells. This enlarges the usual nuclear dimensions by about 10 times, making them large enough to image the detail.
"This is the first time ever that anyone has been able to see in detail, at native genes in vivo, how a transcription factor is turned on, and how it then is activated," said Webb.
Using another method that Webb engineered at Cornell, called fluorescence recovery after photobleaching, the researchers also discovered that HSF activators bind to hsp70 genes much longer than previously thought before being replaced with new HSFs, which raises new questions about the mechanisms of gene transcription.