Beginning in 2004, a group of scientists from around the globe, including two University of Oklahoma faculty members, set out to map the genome of the sea lamprey. The secrets of how this jawless vertebrate separated from the jawed vertebrates early in the evolutionary process will give insight to the ancestry of vertebrate characters and may help investigators more fully understand neurodegenerative diseases in humans.
David McCauley, associate professor in the Biology Department in the OU College of Arts and Sciences, and Sandra W. Clifton, with the OU Center for Advanced Genome Technology, collaborated with scientists from Japan, Germany, the United States, Canada and Great Britain.
McCauley isolated and prepared the liver tissue from the single adult female sea lamprey, from which genomic DNA was isolated for sequencing. Clifton was involved in management of the sea lamprey sequencing project at the Genome Institute at Washington University in St. Louis until her retirement in 2010. The project then was taken over by Patrick Minx. Clifton participated in the discussions regarding the paper preparation, and she is a senior author on the paper. Sequencing was performed at the Genome Institute and the project was directed by Weiming Li at Michigan State University with funding provided by the National Human Genome Research Institute at the National Institutes of Health.
"The sea lamprey is a primitive jawless vertebrate that diverged from other jawed vertebrates early in the vertebrate ancestry," writes McCauley. "Because of its early divergence from other living vertebrates, the sea lamprey genome can provide insights for understanding how vertebrate genomes have evolved, and the origins of vertebrate character traits. Several important findings arise from sequencing the sea lamprey genome: Vertebrates have undergone two 'whole-genome' rounds of duplication, resulting in multiple copies of many genes present in vertebrates. One outstanding question has been the timing of these duplications in vertebrate history. Results from this project suggest that two rounds of duplication predated the divergence of the ancestral lamprey from modern jawed vertebrates. This result is important for understanding how vertebrate genomes have evolved, and in particular, for understanding if the organization of the genome is common to all vertebrates.
"Most vertebrates contain an insulating layer of cells that surround nerve cells. Cells that wrap around a nerve fiber, or axon, are enriched in a protein known as myelin. The insulating properties of myelin allow signals to be conducted rapidly along the nerve fiber, and the loss of myelin results in numerous neurodegenerative diseases in humans."
McCauley adds that lampreys lack these "wrapped" neurons, suggesting the insulated neurons are specific to jawed vertebrates. "Somewhat surprisingly, the sea lamprey genome contains multiple proteins involved in the synthesis of myelin, including its basic protein. This important finding suggests the origin of myelin predated the divergence of lampreys from the lineage leading to jawed vertebrates, but the role of these proteins in lampreys is not known. Other important findings shed light on evolution of the vertebrate adaptive immune system, and the evolution of paired appendages, such as fins in fish and fore-limbs and hind-limbs in tetrapod vertebrates such as humans and animals."
The findings recently were published in the March issue of Nature Genetics. To read the full article, visit www.nature.com/ng.