Researchers use time-lapse movies to track early cardiovascular development
January 31, 2014
By David Martin
Cinema pioneer Georges Méliès used time-lapse photography to send a rocket to the moon in a film released in 1902. More than 110 years later, University of Kansas School of Medicine scientists are using time-lapse movies to unlock the mysteries of early cardiovascular development.
Developmental biologists Charles Little, Ph.D., and Brenda Rongish, Ph.D., are working with biological physicist András Czirók, Ph.D., to produce the movies. Dynamic imaging has enabled the team to study how the heart and vessels form in quail embryos. Quail heart development looks similar to heart development in humans.
Time-lapse imaging is helping the team make observations that elude researchers working with simpler tools. "As a developmental biologist, taking static pictures of embryos viewed under a microscope at multiple time points is time-consuming," says Rongish, an associate professor of anatomy and cell biology.
In addition, a lot happens in the life of an early embryo. The time-lapse movies paint a more detailed picture in three-dimensional space and are less labor intensive.
"If you just have a starting point and an end point, you don't know what happened in between," Rongish says. "We now actually know what happens in between, because we have many more data collection points."
Birds in a flock
The story of the researchers' collaboration begins in Budapest.
Little, a professor of anatomy and cell biology, was on the faculty at the Medical University of South Carolina when he went to Hungary and the Czech Republic to promote international collaboration on behalf of the National Science Foundation.
At a science meeting in Budapest, Little heard Czirók, then a Ph.D. student, talk about the collective behavior of bacteria. Bacteria, scientists have discovered, form cell colonies similar to schooling fish and flocking starlings. "A bird cannot really see the bird on the other side of the flock," Czirók says, "but they still try to avoid collisions."
Little was intrigued by the idea of applying Czirók's expertise in collective motion to embryogenesis, the process by which the embryo forms and develops. Little thought Czirók might help with his "Swan Lake" problem.
Developmental biologists can study how the heart and vessels form by looking at quail embryos under a microscope. The early embryo can be removed from the yolk and kept alive in cell culture for two or three days.
The fragile embryos die if exposed to sustained light, so they cannot be filmed. But still images do not capture the way they grow and change. "It's like saying that if you had 1,000 ballet troupes all doing Swan Lake and you hopped from one to the other every five minutes, you would see Swan Lake perfectly," Little says. "You wouldn't."
Little's vision to perform more dynamic imaging would take time to realize. In 2000, he joined the faculty at KU. The move to Kansas reunited Little with Rongish, whom he had mentored at the Medical University of South Carolina.
Czirók, meantime, completed his Ph.D. at Eötvös University in Hungary. Little invited him to do a post-doctoral fellowship at KU. Today, Czirók splits his time between Kansas City and Budapest. He is an assistant professor of anatomy and biology at KU Medical Center as well as a member of the faculty at Eötvös.
Once ensconced in Little's lab, Czirók applied his skills in math and computer science to the "Swan Lake" problem. He wrote a program that could take images of the quail embryos every five minutes in the first 24 to 48 hours of development and assemble them into time-lapse movies.
Czirók's code stitches together what Rongish calls "a mosaic." She adds: "When you see a movie, you see an embryo. I see eight different image tiles that the software had to put back together to show the entire embryo."
Little says Czirók's program produced so much useful information that storage became an issue. "We have terabytes of data," he says.
Compensating for the current
"From a physics perspective, this work is really interesting," Czirók says. "In biology, we don't understand so many things. How an embryo develops? It's kind of a miracle that all of the sudden you have a functioning organism."
Biochemical signals guide the process to a large degree. As Little puts it: "We understand that genes are the bedrock of life as we know it."
But genetic circuitry does not fully explain how an organism builds its blood vessels. Little and his colleagues believe that collective motion — such as with colonizing ants and the bacteria Czirók studied as a Ph.D. candidate — is the hallmark of morphogenesis, the process by which an organism develops form and structure.
The time-lapse movies have enabled the researchers to perform motion analyses of cardiac and vascular precursor, or pioneer, cells. The team discovered that the cells move with their environment, a network of proteins called the extracellular matrix.
Rongish compares this "tissue motion" to a swimmer in the ocean trying to make it back to a fixed point on the beach. "You have to adjust the way you swim to compensate for the current," she says. "The cells are kind of like that. The general movement is with their surroundings, but they also move to a smaller extent against the current."
Little uses the term "emergent behavior" to describe what makes warm-blooded animals take shape. The process, he says, is not as hardwired as most molecular and cell biologists believe. "There isn't a blueprint in the genome to build an organ," he says. "Organs are like hornets' nests. They are unique, complex structures built by the collective behavior of independent agents."
Instead, the cells obey rules — they try to maximize shear when they are moving, for instance — learned over evolution. "You don't need all that sub rosa information to actuate this physical pattern," Little says.
Czirok applies engineering algorithms to quantify the pattern formation. Most recently, he has developed computer simulations of heart and vessel morphogenesis. He can, for instance, simulate an incision that damages the interconnection between cells and prevents a heart from forming. The model has led to a new understanding of how a myocardial heart tube forms.
Rongish says she is frequently astounded by the ways Czirok's code writing and computational skills enrich the team's more traditional biological research.
"It allows us to quantify things that before people could only guess at," she says. "Having a physicist who is also trained as a biologist has made a tremendous difference for us. We all feel lucky to be part of this multi-disciplinary team, and hope our collaboration will help us uncover the mysteries of blood vessel and heart formation using the tools of biology and physics."