Technique makes it easier to see mouse embryo in all its glory
A fast, high-resolution, 3D mouse embryo visualization technique developed by collaborators at the University of Texas Health Science Center at San Antonio and the University of Utah will revolutionize the way birth defects and cancer genes are studied in animal models. That's the prediction of the researchers in an article to be published online in PLoS Genetics on April 28, a peer-reviewed, open-access journal from the Public Library of Science.
The new tool, called Virtual Histology, has already boosted the researchers' ability to study the mouse embryo and more rapidly focus on abnormalities of development, including childhood cancers. Birth defects are diagnosed in 150,000 babies in the U.S. annually. Suspected causes are genetic abnormalities, environmental insults, and drug and chemical exposures.
Charles Keller, M.D., assistant professor at the Children's Cancer Research Institute (CCRI) at The University of Texas Health Science Center at San Antonio, is studying ways to improve treatment of two types of childhood cancers '" brain tumors called medulloblastomas and muscle tumors called alveolar rhabdomyosarcomas. Dr. Keller, a pediatric oncologist, moved to the CCRI from the University of Utah in 2005, and continues his collaborations with engineers and computer scientists at Utah's Scientific Computing and Imaging Institute. Dr. Keller routinely works with mouse embryos in trying to understand the role of developmentally regulated genes in the types of cancers that children sometimes acquire. The study of genetically modified embryos and their birth defects is usually a slow and laborious process, but Dr. Keller and colleagues have found a way to make the analysis much faster '" and more accurate.
Traditional histology involves embedding embryos in wax, thinly slicing the wax and delicately placing it on slides, staining the sections and viewing slides under the microscope, then mentally reconstructing the three-dimensional aspects of the embryo to reveal pertinent biological information. Under the new method, the intact embryo is stained to distinguish tissues (organs, developing bone and soft tissue) and is digitally scanned at high resolution using x-ray computed tomography. Computational methods are applied to analyze embryo organs for defects.
"From the moment of conception, the mice under study are genetically programmed to develop tumors," Dr. Keller said. "Intentional disruption of specific genes can cause birth defects in the same mice, which teaches us important lessons about how these genes function in both cancer and development." He noted that disruption of a cancer-promoting gene, Pax 3:Fkhr, causes a bone of the nose not to form, for example.
Beyond his own research into the function of cancer-causing genes, Dr. Keller suggests that this technique may have a role in making our households safer. "We make certain assumptions that our toothpaste, artificial sweeteners, pain relievers and household cleaning chemicals are safe for pregnant mothers," he said. "The EPA (U.S. Environmental Protection Agency) and FDA (U.S. Food and Drug Administration) mandate that chemical and drug companies perform tests of reproductive safety, but how complete are these studies? Historically, these studies have been semi-quantitative or subjective. However, microCT-based Virtual Histology allows chemical and drug companies to conduct these studies in a much more quantitative way '" improving upon the safety of the products we find in our homes," Dr. Keller said.
Dr. Keller and a colleague, Michael Beeuwsaert, founded a company called Numira Biosciences (www.numirabio.com) to patent and commercialize discoveries from Dr. Keller's laboratory. Numira plans to make Virtual Histology available to researchers through the sale of kits and imaging services. "Virtual Histology represents a vast improvement in resolution, time and expense compared to current methods and approaches for studying developmental defects in animal models," Beeuwsaert said.
Dr. Keller said Virtual Histology is a timely breakthrough, given the National Institutes of Health's recently announced goal to delete, or "knock out," every one of the 25,000 genes in the mouse genome. "These are exciting times," he said. "Advancements in imaging instrumentation and software tools are helping us understand the genetic basis of mammalian development in unprecedented clarity. It may seem hard to imagine, but putting embryology tutorials on an X-Box for eighth-grade biology students to study the genetic basis of development is already in reach."
Source: Public Library of Science. April 2006
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