Scientists Discover Origins of 'Dark Matter' in Human Genome

Non-coding RNA is the "dark matter" of the genomic world. It doesn't contain the blueprint for making proteins, and yet it comprises more than 95 percent of the human genome. Now, scientists have achieved a major milestone in understanding how this genomic dark matter originates, which could help pinpoint exactly where complex-disease traits reside.

In order to learn a bit more about this non-coding RNA, the researchers set out to identify the precise location of the beginnings of transcription, which is the first step in the expression of genes into proteins. During transcription, DNA is copied into RNA. The scientists determined where along human chromosomes the proteins that initiate transcription of the non-coding RNA were located.

"We took this approach because so many RNAs are rapidly destroyed soon after they are made, and this makes them hard to detect," said B. Franklin Pugh, one of the researchers, in a news release. "So rather than look for the RNA product of transcription we looked for the 'initiation machine' that makes the RNA. This machine assembles RNA polymerase, which goes on to make RNA, which goes on to make a protein."

In fact, the researchers discovered that there were 160,000 of these "initiation machines." This was particularly surprising since humans have only about 30,000 genes. In addition, fewer than 10,000 of these machines were actually found right at the site of the genes. The remaining 150,000 initiation machines were not and still remain somewhat mysterious.

"These non-coding RNAs have been called the 'dark matter' of the genome because, just like the dark matter of the universe, they are massive in terms of coverage--making up over 95 percent of the human genome," said Pugh. "However, they are difficult to detect and no one knows exactly what they all are doing or why they are there. Now at least we know that they are real, and not just 'noise' or 'junk.' Of course, the next step is to answer the question, 'what, in fact, do they do?'"

The findings are important for understanding this "dark matter" of the genome. In addition, it could bring researchers one step closer to solving the problem of "missing heritability."

The findings are published in the journal Nature.