Using a powerful new technique, investigators at the Ludwig Institute for Cancer Research and the National Cancer Institute have identified all the genes that are active in a single cell. The results, which are published this week in the Proceedings of the National Academy of Sciences, point to the type of data that are needed to understand the human genome.
"Now that we know there are roughly 35,000 human genes, the next step is to determine what these genes are actually doing in both healthy and diseased cells," said the study's lead author, Dr. Victor Jongeneel of the Ludwig Institute for Cancer Research, Lausanne, Switzerland Branch.
Analyzing two different cell lines (one from normal breast tissue and the other from colon cancer) the team found that each cell expressed between 10,000 and 15,000 genes, suggesting that human cells may only utilize only one-third to one-half of all genes.
Moreover, the researchers found that nearly 60% of the genes were expressed so weakly that it would have been impossible to determine their activity if it wasn't for a new sequencing method, called massively parallel signature sequencing (MPSS). The technique can track down a single copy of messenger RNA, which indicates the full activity of a particular gene.
"This is the first time that this depth of analysis has been possible," said Dr. Andrew Simpson of the Ludwig Institute for Cancer Research. "The implication is that there is an enormous amount of discovery still to be made on the function of genes."
Indeed, the MPSS technique found more evidence for gene activity than actual genes. Based on the messenger RNA sequence tags that could not be linked to known genes, the results suggest that there may be 2,000 active, but still unaccounted for genes in the two cell types studied. Some of these genes are likely to be hiding in parts of the genome that have yet to be sequenced.
Given the importance and expense of mapping individual cell types, the researchers call for a publicly available MPSS database, similar to the one developed for the Human Genome Project.
"Clearly, there is an enormous and largely untapped value in producing this type of information," said Dr. Jongeneel.
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