Scientists are now able to produce zebra fish who deserve the bizarre names given to them: half-baked, avalanche, speed bump, zombie, ogre, lost-a-fin, piggy tail, snow white, bashful, sleepy, cyclops, mind bomb, uncle freddy, dogeared, van gogh, silentheart, and throbless. Not your typical names for fish often sold to people setting up their first aquariums. However, with a little gene mutation, most of these names are quite appropriate (we may never know for sure about uncle freddy, though. Small groups of scientists around the world have been working to generate embryos of zebra fish whose development was lethally interrupted by a single gene mutation.
The simplified process of achieving these embryos begins with taking a male zebra fish and dunking it in the chemical mutagen ethylnitrosourea. These fish are then bred to create mutated embryos. These mutations effected the embryos in a myriad of ways, such as miswired nervous systems, pigmentation defects, eye abnormalities, and tail malformations, and undeveloped muscles. Several mutations disrupted epiboly, the very first cellular movement of the embryo. The zebra fish embryo depends on a yolk-laden cell until they can feed themselves. During normal epiboly, the cells spread over the yolk. The research ultimately identified mutations in about 600 specific genes.
Many varieties of heart mutations were discovered. These mutants have established thathearts are assembled by sets of genes that are responsible for discreet parts of the organ. It is hoped that by researching the mutants, the scientists will be able to understand why congenital heart disease occurs in humans. Zebra fish with improper blood formation have also been developed. One mutated zebra fish named dracula died when it was exposed to light. The red blood cells became fluorescent and popped. It was originally though that this mutant developed no blood, but it was later discovered that if the fish was raised in he dark, it would have blood. However, an enzyme deficiency makes the blood pigment sensitive to light. There are related enzyme deficiencies, called porphyrias, that cause human diseases.
It is the hope of these scientists that by studying the mutated genes of these fish they will be able to identify and clone all of the genes used by a developing vertebrate embryo. In the past year, they have made many advances. They observed that the shield tissue of the zebra fish embryo signaled the animal cap to start developing into part of the nervous system. For the first time, a cell had been identified in the embryo that could induce neural tissue. By identifying the genes responsible for disturbed nervous systems in the mutants, the scientists hope to discover the exact nature of the signals.
Scientists have almost entirely mapped out the genetic structures of the zebra fish by studying the mutants. This knowledge allows them to hone in on the genes of the fish much faster. The faster the genes can be identified, the faster they can be cloned. The ultimate purpose of the zebra fish mutations is to clone vertebrates. Even though this has already been accomplished with Dolly, the infamous sheep, research has not stopped. Besides cloning live animals, scientists could replace mutated genes in humans that are causing diseases if they can effectively clone "healthy" genes. While the prospect of human cloning and its ramifications frightens many, gene cloning has other uses. Many now incurable diseases could be brought under control with the development of this new technology. It can take a lone researcher up to a year to clone a single gene, but new techniques are allowing this branch of science to develop much more rapidly. A group of scientists in Massachusetts hopes to be able to clone all the genes to make a vertebrate by 1999. It's amazing what science and a zebra fish names dracula can accomplish.
