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Genes replicate like the hairs of the Monkey King
By He Sheng (China Daily)
Updated: 2004-04-20 09:06
Chinese scientists announced recently that they have discovered a novel
mechanism in the genesis of genes, the building blocks of all organisms on
Earth. Their research shows genes are continuously created and altered through a
process known as gene fission.
The new genes originate by copying their ancestral gene, which partially
degenerates during the process, according to the researchers.
This finding confirmed a hypothesis long held by biologists that duplication
is one of the major ways for genes to evolve.
Their gene genesis mechanism also suggests that the genome of the fruit fly,
the living organism their research is based on, is highly flexible and that even
seemingly fixed genes are constantly evolving. Genome refers to the totality of
all the genes in the chromosomes of an organism.
This research was done by an international team involving Chinese and
American scientists and the finding was published in the latest issue of the
scientific journal Nature.
Biologists have been curious about the origin and evolutionary history of
genes ever since two US researchers discovered their key role in shaping life 50
years ago.
It has been found that different organisms vary greatly in the number of
genes contained in their chromosomes, suggesting the origination of new genes
and their evolution is the fundamental issue in the evolution of life, said Wang
Wen, a researcher at the Kunming Institute of Zoology under the Chinese Academy
of Sciences.
Understanding of the mechanism underlying that process may not enrich our
knowledge about all forms of life on Earth, but may contribute to the
development of new drugs, Wang said.
Yet most genes were created so long ago that many mutations occurred during
their evolutionary process, making it very difficult to figure out their early
history. "That's why discussion over this issue has long been on a theoretic
basis," he added.
Wang and his colleagues then looked for young genes - those that had
originated within the last one to two million years - to observe the early
stages of gene creation.
The researchers identified a group of genes in three subspecies of the fruit
fly that diverged less than a million years ago.
Each subspecies has a parental gene sequence on one chromosome and different
numbers of new copies on different chromosomes.
The new copies are very young genes in evolutionary terms - some of which are
the youngest ever discovered - and so all the intermediate steps from the
original parental sequence to the newest copies are visible, according to the
researchers.
They named the gene family "monkey king," after the mythical Chinese hero who
can transform his hairs into offspring.
They observed that one single ancestral gene in the family - containing two
functional domains - duplicated to produce a copy that lacks partial segments
that function to encode proteins.
"One domain in the ancestral gene degenerates, then the new, degenerate gene
duplicates, and that also degenerates and destroys the other domain," said Long
Banyuan, another researcher involved in the discovery.
Their discovery has thus shed new light on the classic model of gene
duplication that suggests the whole gene is duplicated intact without
degenerations, Wang said.
Another interesting aspect of the discovery is that it shows genes may not
necessarily follow the evolutionary process from the simple to the complex, as
previous hypotheses hold.
Their observations of the monkey king gene groups found that the new gene
copies appeared to be simpler than the ancestral one.
"When people think about evolution, they intuitively expect it to take some
sort of direction towards more complexity - that is, multi-domain proteins with
more complex functions," said Berend Snel, from the Centre for Molecular and
Biomolecular Informatics at the University of Nijmegen in the Netherlands.
"Sometimes, there's no such direction. That's why gene fission, I think, has
been overlooked by some people," he commented.
Wang and his colleagues have been leading in the world in the search for
young genes and so far have identified scores of such genes, including the first
RNA gene discovered, the sphinx.
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