By Robin Ann Smith
Any movie that begins with an extreme close-up of the back side of a fruit fly — the same kind found feeding on over-ripe tomatoes and bananas in your kitchen — may seem like an unlikely candidate for action blockbuster of the year. But this is no typical movie.
Duke biologists Dan Kiehart and Serdar Tulu recorded this 3D close-up of a developing fly embryo using new super-resolution microscope technology developed by Eric Betzig, one of the winners of the 2014 Nobel Prize in Chemistry.
Cutting-edge microscopes available on many campuses today allow researchers to take one or two images a second, but with a new technique called lattice light-sheet microscopy — developed by Betzig and colleagues and reported in the Oct. 24, 2014, issue of Science — researchers can take more than 50 images a second, and in the specimen’s natural state, without smooshing it under a cover slip.
Kiehart and Tulu traveled to the Howard Hughes Medical Institute’s Janelia Farm research campus in Ashburn, Virginia, where the new microscope is housed, to capture the early stages of a fruit fly’s development from egg to adult in 3D.
Fruit fly embryos are smaller than a grain of rice. By zooming in on an area of the fly embryo’s back that is about 80 microns long and 80 microns wide — a mere fraction of the size of the period at the end of this sentence — the researchers were able to watch a line of muscle-like cells draw together like a purse string to close a gap in the fly embryo’s back.
The process is a crucial step in the embryo’s development into a larva. It could help researchers better understand wound healing and spina bifida in humans.
Their movie was assembled from more than 250,000 2D images taken over 100 minutes. The hundreds of thousands of 2D snapshots were then transferred to a computer, which used image-processing software to assemble them into a 3D movie.
“This microscope gives us the highest combination of spatial and temporal resolution that we can get,” Kiehart said.
Betzig won this year’s Nobel Prize for his work on techniques that allow researchers to peer inside living cells and resolve structures smaller than 200 nanometers, or half the wavelength of light — a scale once thought impossible using traditional light microscopes.
Even finer atomic-scale resolution has long been possible with microscopes that use beams of electrons rather than light, but only by killing and slicing the specimen first, so living cells and the tiny structures in motion inside them couldn’t be observed.
Betzig and collaborators Wesley Legant, Kai Wang, Lin Shao and Bi-Chang Chen of Janelia Farm Research Campus all played a role in developing this newest microscope, which creates an image using a thin sheet of patterned light.
The fly movie is part of a collection of videos recorded with the new technology and published in the Oct. 24 Science paper.
One video in the paper shows specialized tubes inside cells called microtubules — roughly 2,000 times narrower than a human hair — growing and shrinking as they help one cell split into two.
Other videos reveal the motions of individual cilia in a single-celled freshwater creature called Tetrahymena, or cells of a soil-dwelling slime mold banding together to form multicellular slugs.
Kiehart and Tulu will be going back to Janelia Farm in January to use the microscope again.
“For this visit we’re going to zoom in to a smaller area to look at individual cells,” Tulu said.
“Waking up the morning of October 8 and hearing on the radio that our paper includes a Nobel Prize winner was pretty special,” Kiehart said.
CITATION: “Lattice light-sheet microscopy: Imaging molecules to embryos at high spatiotemporal resolution,” Chen, B.-C., et al. Science, October 2014. http://www.sciencemag.org/content/346/6208/1257998