Maine Perspective Front Page
The Basics of Bones
Nothing could be more basic about the human body than bones. Everything else is tucked into the skeletal framework like furniture in a house. It would seem that medical science ought to know bones well. At the finest scale, researchers should understand how they grow, what gives them strength and why they may ultimately bend or weaken with old age. Not so.
The basics of bone cell biology are revealing themselves slowly under the probing eyes of team of UMaine researchers. Susan Hunter, an associate professor in the Department of Biological Sciences, and her students are working with scientists at Jackson Laboratory in Bar Harbor, Pennsylvania State University and Washington University to understand how bone cells accomplish the many tasks needed to construct the human skeleton.
Hunter's collaborators include Luanne Peters, a highly respected cell biologist at Jackson Lab and a recipient of a UMaine Ph.D. in zoology in 1988, and Carol Gay, professor of cell biology at Penn State who received a bachelor's degree in zoology at UMaine in 1962. During Hunter's graduate years at Penn State, she worked with Gay before receiving her Ph.D. in 1980. Their Washington University colleague is Professor Philip Osdoby.
This team has been studying the fine points of bone cell function and structure. They have focused on one of the key ingredients, the membrane skeleton, a protein network underlying and connected to the cell's outer skin. Their work got a boost this summer with the completion of a thesis by one of Hunter's graduate students, Eric Osborne, a former Bangor resident now attending medical school at the University of New England.
Osborne established the presence of a key membrane skeletal component, ankyrin, in a specific type of bone cell known as an osteoclast. He identified the gene, the DNA sequence which provides the code for the ankyrin protein, and he identified where the compound resides in the cell.
"Ankyrin is a key component in a variety of cells," says Hunter. "It acts like an anchor. It connects spectrin, which is the major fibrous protein in the membrane skeleton, to a variety of other proteins in the cell membrane."
It's possible, says Hunter, that by doing so, ankyrin performs a vital role in strengthening cell membrane and helping the bone cell to communicate with other cells in the blood or marrow.
The research team is also taking clues from the presence of ankyrin in other cells. "In the case of red blood cells, we know that when they are deficient in ankyrin, they can have a variety of problems. Some of them can be quite lethal. There are potentially a lot of places where there could be a defect," says Hunter.
Hunter began her own work at Penn State working with avian bones. Because they grow quickly, they provide scientists an excellent model system for studying bone development. However, much of the team's future work will focus on mice. The Jackson Lab has discovered a mouse that is deficient in ankyrin. This year, Hunter and her colleagues found this mouse also has low bone density.
"The importance of the mouse model can't be overemphasized," says Hunter. "There are a lot of molecular probes, markers and antibodies directed against mouse proteins. Because we have this known mutant, we'd be nuts not to study it. The combination of a known protein mutation and a skeletal defect suggests a connection between the membrane skeleton inside the cell and the skeletal system of the body."
Hunter is on sabbatical this year at Penn State where she will continue working with chicken bones. As a visiting scientist at Jackson Lab, she will also be preparing to shift part of her attention to the mouse model.