Karp's team considered two samples of mice. The first consisted of embryonic mice at various stages of development while the second was composed of adult mice to which two-thirds of their liver were removed. Using techniques such as DNA microarrays which determine which genes are active in a cells and software programs that analyze the collected information, the scientists listed all the proteins that help the cells grow and proliferate in both samples.
The results were unexpected. The researchers noticed that only a few proteins were common to both processes. Proteins called transcription factors, which affect DNA in the cell's nucleus, were highly involved in the development of embryos' livers but not in adult liver regeneration. Instead, proteins that help cells proliferate were active in both the developing and regenerating livers.
These findings showed that a regenerating liver does not behave as a developing embryo. Instead, regeneration could actually be only due to an increase in cells that multiply through regular cell divisions, a process called hyperplasia.
The new results may also have important medical implications. Transcription factors are known to be more difficult to manipulate than the other identified proteins. Since the transcription factors were not present in regenerating livers, it might be easier to stimulate liver regeneration by only activating the other identified proteins.
"These results are very encouraging," Karp says. "Not only did we discover that the number of proteins involved in liver regeneration is relatively low, but they don't include transcription factors, so we may be closer to being able to stimulate liver regeneration than we thought."
The next step will be for scientists to understand wheth
Contact: Pat Pages
American Society for Biochemistry and Molecular Biology