News: Study finds value in 'junk' DNA

Study finds value in 'junk' DNA

For about 15 years, scientists have known that certain "junk" DNA --
repetitive DNA segments previously thought to have no function -- could
evolve into exons, which are the building blocks for protein-coding genes in
higher organisms like animals and plants. Now, a University of Iowa study
has found evidence that a significant number of exons created from junk DNA
seem to play a role in gene regulation.

The findings, which increase understanding of how humans differ from other
animals, including non-human primates, appear Oct. 17 in the open-access
journal PLoS Genetics.

Nearly half of human DNA consists of repetitive DNA, including transposons,
which can "transpose" or move around to different positions within the
genome. A type of transposon called retrotransposons are transcribed into
RNA and then reintegrated into the genomic DNA. The most common form of
retrotransposons in the human genome are Alu elements, which have more than
one million copies and occupy approximately 10 percent of the human genome.

"Alu elements are a major source of new exons. Because Alu is a
primate-specific retrotransposon, creation of new exons from Alu may
contribute to unique traits of primates, so we want to better understand
this process," said the study's senior author Yi Xing, Ph.D., assistant
professor of internal medicine and biomedical engineering, who holds a joint
appointment in the University of Iowa Carver College of Medicine and the UI
College of Engineering.

To study the impact of Alu-derived exons on human gene expression, the
researchers used a high-density exon microarray. The technology has nearly
six million probes for monitoring the expression patterns of all human
exons. Using data generated by these microarrays, the scientists analyzed
330 Alu-derived exons in 11 human tissues. The team then identified a number
of exons with interesting expression and functional characteristics.

"Hundreds of exons in the human genome were created from Alu elements. The
whole-genome exon microarray allowed us to quickly identify exons that most
likely contribute to the regulation of gene expression and function," said
Lan Lin, Ph.D., University of Iowa postdoctoral fellow in internal medicine
and the lead author of this study.

Analysis of one human gene, SEPN1, which is known to be involved in a type
of muscular dystrophy, along with comparative data from chimpanzee and
macaque tissues, suggested that the presence of a muscle-specific
Alu-derived exon resulted from a human-specific change that occurred after
humans and chimpanzees diverged evolutionarily.

"In this case, this exon is only expressed at a high level in the human
muscle but not in any other human or non-human primate tissue, so this
implies that the exon plays a functional role in muscle, and this role is
human-specific," said Xing, who is also affiliated with University of Iowa
Center for Bioinformatics and Computational Biology.

Source: University of Iowa
http://www.physorg.com/news143438347.html

Posted by
Robert Karl Stonjek


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