Scientists find key cichlid gene

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Molecular biologists have found a gene which they believe may be responsible for the speciation and morphological diversification of Lake Victoria cichlids.

The gene is closely related to one found in humans which causes a human disease that leads to facial defects, and scientists believe that changes in the gene might have led to the huge variation of jaw and mouth structures seen in African lake cichlids.

There are over 300 species of cichlid in Lake Victoria and most of the differences between species are confined to colouration and the morphology jaw area.

The changes have allowed the fish to undergo an adaptive radiation in which hundreds of species have evolved to feed on different types of food, without competiting with other species.

DNA studies over the past decade have also shown that Lake Victoria cichlids are also remarkably similar in their genetics, and sophisticated techniques have had to be employed to study the small differences in the DNA of related fish.

MicroarraysThe team of scientists from the Tokyo Institute of Technology, who are due to publish their findings in the molecular biology journal Gene, used a sophisticated technique using a DNA microarray or gene chip to find certain genes that were being expressed in the cichlid DNA.

One of the genes identified, called microfibril-associated glycoprotein 4 (magp4), is known to cause a disease called Smith-Magenis Syndrome (SMS) in humans.

Smith-Magenis Syndrome causes facial defects, and further studies on the cichlids showed that the magp4 gene was being expressed in the jaws of cichlid fry, and that different species such as Paralabidochromis (Haplochromis) chilotes and Paralabidochromis (Haplochromis) sp. "Rock Kribensis" differed in the way the gene worked.

They believe the gene might be the one responsible for the diversification of the cichlid jaw that has led to the adaptive radiation of these fish.

Previous scientists have said that the jaw and pharyngeal area of cichlids represents a key evolutionary innovation. The jaw and pharyngeal area is one of the most important anatomical features in cichlid systematics.

For more information see: Kobayashi N, Watanabe M, Kijimoto T, Fujimura K, Nakazawa M, Ikeo K, Kohara Y, Gojobori T, Okada N (In press) - magp4 gene may contribute to the diversification of cichlid morphs and their speciation. Gene, 2006 (in press).