UO zebrafish help explain egg-spots on African cichlids' fins

A male haplochromine cichlid with characteristic egg-spots on its anal fin

Ingo BraaschSwiss scientists, with the help of a University of Oregon postdoctoral fellow working with genetically modified zebrafish, have unlocked the origins of the colorful fin markings called egg-spots on male African cichlid fish.

Some 1,500 species in egg-spot bearing haplochromines, a group of African cichlids, sport the markings on their anal fins, and they play a central role in the mating behavior of these mouth-breeding fish. The evolution of the spots, which don't appear in other groups, has been in a long-running scientific mystery.

The egg-spots, it turns out, evolved in cichlids benefitting from mobile genetic elements, or "jumping genes," that led to new gene activities in the pigment cells building the egg-spots, report two researchers at the University of Basel who led a study published in the journal Nature Communications. Ingo Braasch, who works in Institute of Neuroscience laboratory of John Postlethwait, is a co-author on the paper.

"Testing the functional consequences of genetic variation between different species is very difficult in cichlids, because genetic manipulations are impeded especially in mouth-breeding species," Braasch said. "We switched to the zebrafish as model system and developed a functional test here at the UO."

Braasch inserted the regulatory genetic elements that can switch on genes from cichlids that carry the egg-spots and those that don't, connecting them with a fluorescent reporter gene, into the zebrafish genome. Resulting zebrafish carrying genetic elements from cichlids with egg-spots showed fluorescence in their pigment cells, while the others did not.

"This suggests that the mobile genetic element specifically present only in egg-spot bearing cichlids drives gene activity in pigment cells in the egg-spot," Braasch said. "It also shows how zebrafish -- developed as a model system here at the UO -- can be used as a functional hub to study the evolution of gene functions even among distantly related fish species such as cichlids. This is similar to studies that have used mice to study the functional consequences of genetic differences among human populations."

In addition, he said, genetic data collected by the Zebrafish Model Organism Database  (ZFIN) hosted at the UO were instrumental in providing leads into the possible function of the involved genes.

For a more scientific explanation, see "The Cichlids’ Egg-Spots: How Evolution Creates new Characteristics" story issued by the University of Basel.

By Jim Barlow, Public Affairs Communications