June 9, 2008 -- Researchers at Duke Medical Center (Durham, NC) say they have glimpsed the formation of blood vessels during development -- with the help of green fluorescence and time-lapse microscopy.
The research team, led by cell biologist Blanche Capel, Ph.D., has found a previously unknown mechanism in the formation of blood vessels that it hopes will help scientists better understand how a tumor rallies a blood supply to its aid.
Using mice that have blood vessel cells marked by green fluorescence, the Duke University cell biologists studied vessels that supply mouse gonads (the embryonic organs that give rise to ovaries or testes). The microscope took 3-D pictures of an embryonic mouse organ over 24 to 48 hours.
The scientists' system answered key questions about how the vasculature gets fitted into the organ as it forms, Capel said. Before this, scientists could only image one point in development at a time.
The Duke team was surprised by the vigorous cell movements involved in the development of male gonads. "In the male gonad, the major blood vessel in the adjacent tissue comes apart and the individual blood vessel cells move to a new location, and reassemble into new vessels inside the testis," Capel said. "This breakdown process represents a possible way for growing tumors to access a blood supply, by commandeering a mechanism similar to the ones organs use to recruit vessels into the tumor."
She pointed out that a blood supply is critical to a growing tumor, and this may be an important mechanism in the formation of blood vessels in tumors that scientists have not appreciated before. "That is an exciting finding," Capel said.
This imaging in 3-D over time was possible because Capel's laboratory already had developed a culture system for studying the organ in the lab. "We were positioned to convert that to a live imaging system when advances in microscopy became available at Duke University Medical Center," Capel explained. "The Duke Department of Cell Biology has an imaging facility that is really outstanding, and our chair, Brigid Hogan, has put a lot of energy into making sure it is state of the art. One of the authors on this paper, Tim Oliver, who manages this facility, helped us to get the imaging set up."
The organs were placed in small wells in an agar block designed to hold them still. The entire system was enclosed in a humidified and temperature-controlled chamber around the microscope. Scientists captured an image every 20 minutes for 24-48 hours, then later assembled the images in sequence to make movies.
It wasn't easy, Capel said. "We had to work a lot of kinks out of the system. For example, we were exposing the organ to a laser to detect the fluorescent vascular cells throughout the duration of the culture. But too much laser light damages cells. You need to create a bright enough fluorescence in the cells so that you don't have to turn the laser on such a high setting that it kills cells during the culture period."
This success with recording the growth of blood vessels has spurred the Capel lab team on to new projects. "Our goal now is to have different colored fluorescent markers for other types of cells in the organ. I hope we can simultaneously image the vessels and other cells as the vessels move into the organ, so we can see how they interact together as a functional organ is forming."
The images became the cover story of the Proceedings of the National Academy of Sciences.
Recently, Duke researchers reported other progress in cellular imaging: how femtosecond-laser pulse and pulse-train shaping allow detection of new nonlinear effects with modest powers, making many new biomarkers accessible and permitting deeper tissue imaging than conventional microscopy.