Using cryo-electron tomography, the scientists compared the structures of the rod outer segment in the mutant mice to those in normal mice.
"This is one of the few places in the world where you could do this," said Wensel. The Center, run by Chiu, has powerful cryo-electron microscopes that make tomography possible. To achieve the three-dimensional reconstruction, Dr. Juan T. Chang (http://www.bcm.edu/pda/index.cfm?PMID=8208) in Chiu's Center froze the photoreceptors purified by then-graduate student Jared Gilliam in a special way that made it possible to perform electron microscopy. During the microscopy session, the frozen samples were carefully tilted allowing the researchers to take many two-dimensional images that were used in the computer reconstruction of the three-dimensional map.
The light-sensing outer segments of photoreceptors in the retina are connected to the machinery responsible for protein production in the inner segment by a thin cylindrical bundle of microtubules known as the connecting cilium.
"There is a huge flux of material from the inner segment to the outer segment of the photoreceptor," said Wensel. "When there is a defect, then the animal or patient goes blind."
The three-dimensional structure showed that there are vesicles (small sacs) tethered to membrane filaments.
"It looks as though these vesicles that are tethered contain material that will fuse to the plasma membrane and go up the membrane to the outer segment," said Wensel.
In studies of a mouse model of a d
|Contact: Graciela Gutierrez|
Baylor College of Medicine