In 1665, the English polymath Robert Hooke declared boldly: “By the help of microscopes, there is nothing so small as to escape our inquiry.” Three and a half centuries later, his proclamation, though perhaps still slightly hyperbolic, is more true than ever.
Advances in microscopy and optics allow biologists to peer with unprecedented resolution at the inner workings of living cells. Moreover, 21st-century technology gives researchers the ability to observe in real-time the effect of their experimental manipulations.
Unfortunately, the price of a modern microscope is significantly higher than in Hooke’s time. With the average optical system costing half a million dollars, a single lab may not be able to afford the tools necessary for its research. To overcome this obstacle, scientists from different university departments are increasingly teaming up at core facilities, where the cost of acquisition and maintenance of equipment is paid by grants and university funding.
One of the best examples of this model is Berkeley’s Molecular Imaging Center (MIC). Since its establishment in 2001, the MIC has become an invaluable resource to Berkeley labs. A joint venture of the Cancer Research Laboratory, the Department of Molecular and Cell Biology, and the Helen Wills Neuroscience Institute, the MIC has grown from incorporating a single microscope (Berkeley’s first two-photon system) to housing more than a dozen systems in two campus buildings.
Holly Aaron, the MIC’s manager, says the center’s instruments are open not only to Berkeley researchers, but also to scientists at the Lawrence Berkeley Lab, UC San Francisco and biotech companies. This equipment includes state-of-the-art confocal laser scanning microscopes, which use oscillating mirrors to rapidly illuminate each point on a sample, over and over again (hence “scanning”). The reflected light is then filtered through a pinhole to eliminate out-of-focus signal, producing images with very fine resolution, down to the nanometer scale. At this dimension, researchers can see, for example, the dendrites of a single neuron, or the mitotic spindles of a dividing cell. Another piece of equipment is the relatively new light-sheet system, which offers imaging speeds up to 50 times faster than a confocal microscope. Finally, inverted microscopes are available for imaging of samples that cannot be put on a slide, such as living cells in culture.
The MIC’s instruments are being used in a range of projects. Colleen Kirkhart, a neuroscience graduate student, researches fruit flies’ sense of taste. Specifically, she is interested in how flies can remember that certain foods taste sweet or bitter. In her experiments she is examining an area of the insect’s brain called the mushroom body—about the size of a fine grain of sand—because this region has long been known to be important for learning and memory.
“I’m trying to understand the neural circuitry underlying the fly’s ability to form and store taste memory,” says Kirkhart. The MIC’s microscopes allow her to carefully pinpoint the anatomical areas she is interested in and label them using a photoactivatable protein. The technique essentially gives her the ability to trace neural circuitry using light. Having the MIC as a resource greatly expands Kirkhart’s range of technical possibility, since she is not limited to using the instruments owned privately by her lab. “I can attempt any new, state-of-the-art method I want to try, providing me a level of experimental freedom I wouldn’t otherwise have,” she says.
The field of microscopy is barreling ahead: tools undreamt of even 20 years ago are now somewhat antiquated. As the MIC expands, its microscopes will illuminate ever smaller biological processes with ever greater resolution. In the not-too-distant future, Hooke’s fanciful assertion may become reality after all.