Mice thrive without 'junk DNA' 20/10/04. By the DOE Joint Genome Institute Researchers have deleted 3 per cent of the mouse genome, but the mice show no apparent ill effects.

After completing the sequencing of the human genome, a question still lingers: is all the non-coding DNA (sometimes called 'junk DNA') – which makes up nearly 98 per cent of the genome – required, or is some of it potentially disposable?

US researchers have now shown that deleting large swaths of DNA sequence shared by mice and humans still generated mice that suffered no apparent ills from their genomes being millions of letters lighter.

The findings, by researchers at the US Department of Energy Joint Genome Institute (JGI) and Lawrence Berkeley National Laboratory, were published in the 21 October 2004 edition of the journal Nature.

"In these studies, we were looking particularly for sequences that might not be essential," said Eddy Rubin, Director of the JGI, where the work was conducted. "Nonetheless we were surprised, given the magnitude of the information being deleted from the genome, by the complete lack of impact noted. From our results, it would seem that some non-coding sequences may indeed have minimal if any function."

A total of 2.3 million letters of DNA code from the 2.7-billion-base-pair mouse genome were deleted. To do this, embryonic cells were genetically engineered to contain the newly compact mouse genome. Mice were subsequently generated from these stem cells. The research team then compared the resulting mice with the abridged genome to mice with the full-length version. A variety of features were analysed, ranging from viability, growth and longevity to numerous other biochemical and molecular features. Despite the researchers' efforts to detect differences in the mice with the abridged genome, none were found.

The negligible impact of removing these sequences suggests that the mammalian genome may not be densely encoded. Similar-sized regions have previously been removed from the mouse genome, invariably resulting in mice that did not survive, because the missing sequences contained important genes and their deletion had severe consequences for the animal.

Adapted from a press release by the DOE Joint Genome Institute .

Links

Nobrega M A, et al. (2004) Megabase deletions of gene deserts result in viable mice. Nature 431: 988-93. Abstract