By Krishna Ramanujan
Scientists thought that most new genes were formed from existing
genes, but Cornell researchers have discovered a gene in some fruit flies
that appears to be unrelated to other genes in any known genome.
The new gene, called hydra, exists in only a small number of species
of Drosophila fruit flies, which suggests it was created about 13 million
years ago, when these melanogaster subgroup species diverged from a common
ancestor.

And early evidence indicates that the new gene is functional (as
opposed to being nonfunctional "junk" DNA) and is likely to express a
protein involved in late stages of sperm cell development (spermatogenesis).
This finding is consistent with work of other scientists who are discovering
that many of the most recently formed functional genes in any species also
are expressed in male testes and appear related to spermatogenesis.

"This is a de novo -- 'out of nowhere' -- gene," said Hsiao-Pei Yang,
a senior research associate in Cornell's Department of Molecular Biology and
Genetics and senior author of a paper published in the July 6 issue of the
online journal PLoS Genetics (Public Library of Science Genetics). "People
used to think that new genes were always formed from tinkering with other
genes, but with this gene we can find no homologues [genes with a similar
structure]. You cannot find any related genes in the fly genome or any
species' genome, and that is what is unique."

Yang conducted part of this research while at the National Yang-Ming
University in Taiwan and part of the work in collaboration with Cornell's
Daniel Barbash, assistant professor of molecular biology and genetics.

The researchers do not yet know how the hydra gene was created, but
they speculate that the gene may have developed from a piece of DNA junk
called a transposable element (also known as a "jumping gene"), which may
have been inserted into the genome by a virus. These transposons are known
to copy and insert themselves into DNA sequences. For example, one theory is
that when a transposon sits next to a gene and then jumps to a new location,
it carries part of the gene sequence it was next to and inserts it in the
new location. Often, transposable elements appear to have no function or may
be harmful and are eliminated by natural selection, but researchers are
beginning to think transposons may be a source for creating new functional
genes as well.

The hydra gene is named after the Greek mythological beast that had a
hound's body and nine snake heads, because it has nine duplicated first
exons (sections of the gene that contain protein-coding information). Each
of these exons may serve as alternative starting positions for the gene to
become activated. The researchers found that most of these exons had a
sequence for a transposable element sitting right next to it. Duplicated
sequences generated by transposons may be part of the mechanism for creating
new genes, as the duplications provide more chances for a gene to evolve.


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