Cichlid fish provide better understanding of the genetic factors that regulate bone shape

Researchers at the Forsyth Institute have discovered that the genes that influence the jaws of cichlid fish, tropical freshwater fish renowned for head shape diversity, offer insight into overall vertebrate diversity.

The scientific studies led by R. Craig Albertson, PhD., Staff Associate, show that the growth factor gene, bmp4, is both associated with and has the potential to alter jaw morphology in a way that approximates natural variation among fish species.

According to Dr. Albertson, "An understanding of the genetic factors that regulate bone shape is also vital to a better diagnostic comprehension of human craniofacial defects, and could lead to the development of biological therapies for facial traumas."

African cichlid fishes have evolved highly specialized modes of feeding through extensive adaptations of their jaws. This study, published in the current issue of Proceedings of the National Academy of the Sciences, (PNAS), explores the molecular basis of alternate jaw types in this species-rich group.

The opening and closing lever mechanisms of the lower jaw have traditionally been used to describe feeding techniques in bony fishes. Quantitative genetic analyses in cichlids demonstrate that opening and closing jaw mechanisms are regulated by distinct genetic factors, and are free to evolve independently. Allelic variations in bmp4 segregates with the mechanical advantage of closing. Further, species-specific differences in cichlid jaw shape are correlated with different patterns of bmp4 expression in the embryonic jaw. Finally, when bmp4 is over-expressed in a developmental model organism, the zebrafish, jaw shape changes in a way that parallels natural variation among cichlid species.

"This work provides new insights into the mechanisms that underlie biodiversity," Albertson said. "Moreover, our results show interesting parallels with recent work in another evolutionary model, Galapagos finches." In both studies bmp4 is implicated as underlying adaptive variation in jaw shape. Higher levels of bmp4 result in thicker jaws, whereas lower levels are associated with thinner jaws. The fact that bmp4 may underlie morphological diversity in both birds and fishes, raises the interesting possibility that it might play a broader role in vertebrate evolution."

"Superficial similarities between these two systems may be similar on a molecular level," Albertson adds. "This research is exciting on several levels. We now have the opportunity to explore what genes make a head, and which genes create variations in head shape. Furthermore, this work will help us gain a better understanding of, and offer possibilities for preserving biodiversity of species."

R. Craig Albertson is a Staff Associate and a member of the laboratory of Pamela C. Yelick, Ph.D. in The Forsyth Institute Department of Cytokine Biology. His work is supported through a National Institute of Health training grant awarded to the Forsyth Institute.