By Isabella Chow
A fly has multiple eyes on its wings, antennae, and legs. Fourteen in all. A nightmarish manifestation of a science fiction thriller? Indeed not; this is a true account of a study conducted in Switzerland and reported in the March 24 issue of Science.
Dr. Walter J. Gehring of the University of Basel in Swtizerland, and colleagues Dr. Georg Halder and Dr. Patrick Callaerts, created these macabre creatures by taking copies of the "eyeless" gene (so called because without it, flies have no eyes at all) and inserting it in parts of the primordial fly larva that eventually become wings, legs, antennae and other body parts. Upon maturation, the flies emerged with fully-developed eyes-as many as fourteen on a single fly-in the exact places where the gene had been injected. These inappropriately placed eyes were full-fledged units, not merely superficial imitations of the actual fly eye. They possessed all 800 essential eye units: the red pigment, the bristles between each unit eye, the lens, the light-sensitive cells inside, etc. While the team has determined that the eyes are fully operative, they have not yet discovered if they are wired to the fly's brain. This crucial link decides whether the eyes offer their owners a new and skewed view of the world.
The implications of the finding are far-reaching: there is evidence that the Gehring team has discovered the so-called "master control gene" for the formation of the eye. Growth of different parts of the body is "turned on" by specialized genetic signals. The question that has been plaguing developmental biologists is, "which gene?" The gene that was injected to the flies in the study may in fact be an all-important gene. Dr. Gehrig believes that at least 2,500 different genes are actively involved in the formation of the eye, and that all of these must be indirectly or directly supervised by the "eyeless" gene.
This "eyeless gene's" similarity to a gene identified in humans and other mammals also indicates that scientists may have isolated the gene that directs creation of eyes in our own species. The similarity in this gene may also indicate that mutation of eyes in different species took place only once, rather than multiple times, as is commonly believed. Although humans, flies and squids have very different levels of seeing, due to the differences in their eyes, there is a marked closeness between the genes for mammalian eye formation, fly eye formation, and the squid "eyelessness." This may indicate that the different types of eyes that exist today evolved only once, to be suited to the needs of the organism involved.
Scientists are hopeful that through greater understanding of the growth and development of the eye, they can eventually improve the strategies and therapies currently used to treat visual afflictions.
Source: The New York Times, March 24, 1995. A1.