New York, Nov 04: The genes are accomplished
polymaths, and upto 94 per cent of human genes generate more
than one product, researchers say.
Genome-wide surveys of gene expression in 15 different
tissues and cell lines have revealed that process, called
alternative splicing, can produce mRNA molecules and proteins
with dramatically different functions, despite being formed
from the same gene.
The surveys used high-throughput sequencing to generate
the most detailed portrait yet of how genes are expressed in
different tissues, Nature magazine said quoting new research.
Only about 6 per cent of human genes are made from a
single, linear piece of DNA, the study published in journal
said. Most genes are made from sections of DNA found at
different locations along a strand.
The data encoded in these fragments are joined together
into a functional messenger RNA (mRNA) molecule that can be
used as a template to generate proteins.
But journal says researchers have found that the same gene
can be assembled in different ways, sometimes leaving out a
piece, for example, or including a bit of the intervening DNA
sequence.
The phenomenon provides some solace to those disappointed
by the relatively small number of genes in the human genome:
with around 20,000 genes, humans have roughly the same number
as the elegant but decidedly less complex nematode,
Caenorhabditis elegans, Nature said.
"We were expecting that something as sophisticated,
complex and intelligent as ourselves would have about a hundred
thousand genes at least," says Jacek Majewski, a genomicist at
McGill University in Montreal, Canada. "Then we sequenced the
genome and realised it was about the same number as C elegans."
Fortunately, alternative splicing is thought to occur in
only about a tenth of C elegans genes, restoring the dignity of
complexity to the human genome, researchers say. Understanding
this flexibility should help to reveal how improperly spliced
genes can trigger disease.
Despite intense interest in alternative splicing, Nature
said, the phenomenon has been difficult to study, and the usual
laboratory techniques often fail to detect rare splice forms.
Researchers previously estimated that 74 per cent of all
human genes are alternatively spliced, but recognised that this
estimate was likely to increase as techniques to study the
process improved.
Now two groups, one led by computational biologist
Christopher Burge of the Massachusetts Institute of Technology
in Cambridge and the other led by molecular biologist Benjamin
Blencowe of the University of Toronto in Canada, have studied
alternative splicing using high-throughput sequencing data
generated by Illumina, a biotechnology company based in San
Diego, California.
The technique works by using an enzyme to convert mRNA
back to DNA, which can then be sequenced. Blencowe and his
colleagues studied splice forms found in six different tissues,
including the brain, liver, muscle, and lungs. Burge and his
colleagues used these samples along with several others,
including breast cancer cell lines.
Based on over 400 million sequences, Burge`s team
estimates that 9294 per cent of all human genes can yield more
than one RNA molecule.
Bureau Report
