In a new step to decode information in the human genome, scientists have discovered the location and sequence of over ten thousand DNA regions that function as genetic on-off switches in human fibroblast cells.

In this study, the researchers also developed an efficient method to identify thousands of regulatory sequences in deferent cells, according to a paper published Wednesday in the online version of the journal Nature.

"Promoters are a type of genetic switch that turn gene expression on or off. If we know where the promoters are, we can study how the genetic switches work in a cell, and investigate their connection to human diseases," said lead researcher Bing Ren, an assistant professor at University of California, San Diego.

Although scientists have found most of the protein-coding genes in the human genome, their control sequences have been elusive until now, Ren said.

"Until now, we know that the human genome is composed of about 25,000 genes, but not all the genes are expressed in every cell. For example, about 7,000-8,000 genes are expressed in brain cells, the others have been 'shut off' by promoters," Ren told Xinhua.

Genes are defined by their ability to generate a functional product. Thus the promoter, a DNA sequence that controls when and where a gene product is generated, is the critical element that distinguishes a gene from 'junk DNA'.

Ren's team was able to track critical proteins binding to each gene's promoter to identify 10,567 active promoters, 6,091 of which were previously unknown. He and his colleagues have made the data freely available on online public databases.

Fibroblasts are relatively generic, easily maintained, human cells that form connective tissues throughout the body. By knowing the specific sequences of DNA that control the nearly 8,000 active genes in fibroblasts, scientists can tease apart the promoter system these cells use to turn genes on and off during normal growth.

Features of the map suggest extensive use of multiple promoters by the human genes and widespread clustering of active promoters in the genome. In addition, examination of the genome- wide expression profile reveals four general classes of promoters that define the transcription of the cell, the researchers found.

Understanding the on-off control mechanisms will further understanding of how a cell is programmed to perform specialized functions, said Ren.

"And our study is only the first step. Later we will apply the analyzing method to other cell types, such as the neuron cell and the muscle cell," he said.

"Many research groups are focusing their work in this field. To map all the genome promoters in all human cell types will be a huge project, just like the international Human Genome Project, or even bigger, " he noted.

Source: Xinhua