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