Biologists have long assumed that all jawed vertebrates possess a full complement of nearly identical genes for critical aspects of their development. But a paper in the December 16 issue of Science with Benjamin King of the Mount Desert Island Biological Laboratory (MDIBL) as lead author shows that elasmobranchs, a subclass of cartilaginous fishes, lack a cluster of genes, HoxC, formerly thought to be essential for proper development.
Hox genes dictate the proper patterning of tissues during embryonic development in all bilateral animals, that is, those with a top and a bottom and a back and a front. In fruit flies, mutations in one Hox gene can lead to such miscues as legs growing where antenna should be. In mammals, Hox genes are required for the proper patterning of vertebrae and ribs. Hox genes are notable for being "co-linear," that is, the order they appear in the genome corresponds to the order of their expression in tissues of developing embryos from head to tail.
Fruit flies have one Hox cluster. In all the jawed vertebrates previously studied, scientists always found four copies of the Hox cluster. These clusters, named HoxA, HoxB, HoxC, and HoxD, are present in humans with roughly 10 genes in each cluster (39 in all). Prior to King's study, it was thought that all jawed vertebrates needed at least one gene from each of the four clusters for viable development. However, King and his colleagues call that fundamental assumption into question by offering compelling evidence that at least two elasmobranch fish, the little skate (Leucoraja erinacea) and the dogfish shark (Scyliorhincus canicula), lack the HoxC cluster.
King and his co-authors, Heather Carlisle and Randall Dahn from MDIBL and Andrew Gillis from Cambridge University, used high-throughput sequencing data to characterize all genes expressed in late-stage embryos from three cartilaginous fishes the elephant shark (Callorhincus milii<
|Contact: Ann Cox Halkett|
Mount Desert Island Biological Laboratory