The Laboratory Opossum
While Texas Biomed is well recognized for its extraordinary primate resources, Institute scientists also were responsible for developing another animal model that is increasingly important to biomedical research: the laboratory opossum. Today the Institute is home to a fully pedigreed colony of 2,200 laboratory opossums, and it serves as a world center for research with these animals and for producing them for scientists around the globe.
The laboratory opossum is a small marsupial native to South America known as the gray short-tailed opossum, or Monodelphis domestica. Because of its favorable physical and reproductive characteristics, it has become the predominant laboratory-bred research marsupial in the world today, used as a model organism for comparative research on a broad range of topics that are relevant to human development, physiology, and disease susceptibility. Because Monodelphis mothers produce an extra-uterine fetus, essentially giving birth to their babies at an age equivalent to a six-week-old human fetus, this species is particularly important to research on early development.
At Texas Biomed, research programs with laboratory opossums focus on several key areas.
Institute scientists have shown that infant laboratory opossums exposed to ultraviolet light can spontaneously develop melanoma as adults. This makes the Monodelphis the only mammal other than humans known to be susceptible to malignant melanoma as a consequence of UV radiation alone, offering unique opportunities to develop new prevention strategies and to test new treatments for this most deadly form of skin cancer.
The laboratory opossum also is susceptible to a form of corneal cancer induced by UV radiation, and this susceptibility is highly heritable. At Texas Biomed, scientists are studying the genetic mechanisms that contribute to the disease in hopes of developing a better understanding of the genetic mechanisms that make some individuals resistant and others more susceptible to this and other cancers.
Tackling cancer from a different angle, Institute scientists recently have been successful in transplanting human tumor cells into the laboratory opossum and getting those tumors to metastasize, or spread, before the animal's immune system eventually begins to kill the cancer cells. This is the first time that human cancer cells have been successfully transplanted into another animal with an active immune system, offering unique opportunities to study how the immune system and chemotherapies can work together to fight cancer.
Genetic Influences on Cholesterol
Texas Biomed scientists have shown the laboratory opossum to be a valuable model for dietary-induced hypercholesterolemia, a major contributor to heart disease. Their research has revealed that a single recessive gene is primarily responsible for determining that some opossums are resistant to this condition and others are susceptible. Further investigation is underway to identify the gene and to learn how it functions.
Spinal Cord Injury Repair
Institute scientists are investigating the unique capability of Monodelphis to repair severe spinal cord injuries during the first week of life. The investigators are trying to identify central nervous system genes that switch on or off at this age, rendering the older animals incapable of repairing spinal cord injuries. This work may lead to the development of effective treatments for humans who suffer from these same devastating injuries.
Increasing Role in Genetics Research
It is anticipated that the laboratory opossum will continue to grow in research importance as a result of two recent advancements. At Texas Biomed, scientists have published a Monodelphis gene map. Also, in late 2003, the National Human Genome Research Institute selected the Monodelphis as the first marsupial – and one of the few mammalian species – to have its genome sequenced. Together, the Monodelphis genome sequence and gene map will provide powerful tools for genetic studies involving this increasingly important animal model.