MASTER EYE GENE IDENTIFIED
by Sean Henahan, Access Excellence
WASHINGTON, D.C.- A single gene has been identified that
appears to control the growth and development of eyes throughout
the animal kingdom, report Swiss researchers.
The 'eyeless' gene is believed to be a master control gene
for the growth and development of eyes. The Swiss researchers
demonstrated their hypothesis in a dramatic series of experiments
in which they induced fly eyes to grow on the wings, legs and
antennae of Drosophila fruit flies. They accomplished this by
carefully targeting the expression of the eyeless gene. The
resulting eyes grew in complete with active photoreceptors and
resembled normal fly eyes. One fly had 14 eyes growing out of
various parts of its anatomy.
The current experiments are built on at least 80 years
of research with Drosophila genes. A mutation associated with the
gene- the absence of compound eyes, was first described in 1915
(hence the term 'eyeless' gene). Thirty years ago, while still a
graduate student, the director of the current study, Dr. Walter
Gehring, observed that certain embryonic tissues called imaginal
disks eventually grew into different structures such as eyes or
legs. Later research revealed that mutations in the eyeless gene
resulted in deformed or absent eyes. Gehring and colleagues
conducted the present experiment by inducing the eyeless gene to
express itself in different imaginal disks.
"These findings indicate that this gene is the master
control gene for eye morphogenesis because it can induce ectopic
eye structures in at least the imaginal disks of the head and
thoracic segments. The expression of this gene switches on the
eye development pathway that involves several thousand genes,"
the researchers report in Science.
Homologs of the eyeless gene found in Drosophila have also
been found in a variety of vertebrates (including homo sapiens),
insects, cephalopod, ascidians and nemerteans. The homolog of the
eyeless gene of Drosophila is called the aniridia gene in humans
and Pax-6 in mice. The genes all have much in common, including
extensive sequence identity, the same three intron splice sites,
and similar expression during development.
So what would happen if a mouse eye gene was introduced
into a fruit fly genome? When the researchers induced expression
of the mouse Pax-6 gene in the Drosophila fruit fly, additional
(fly) eyes sprouted at the sites of the gene expression.
"The observation that mammals and insects, which have
evolved separately for more than 500 million years, share the
same master control gene for eye morphogenesis indicates that the
genetic control mechanisms of development are much more universal
than anticipated," note the researchers.
The eyeless gene appears to produce a protein that appears
to be a transcription factor. The current hypothesis is that when
expresses, this protein binds to a specific set of genes and
basically says 'make eyes'. The discovery of this 'master control
gene' will help researchers coordinate the extensive data they
already have on some of the genes involved with the development
of vision, and will also probably reveal the presence of many
other vision-associated genes
The complete data from the fly eye experiments appeared in
Science, Halder et al., v.267, pp 1788-1792, 3/24/95.
Transmitted: 95-03-30 21:06:19 EST
Related information at other Web sites
WWW Virtual Library: Drosophila