March 2, 2013
Geneticists Complete Sea Lamprey Genome Sequencing
Brett Smith for redOrbit.com - Your Universe Online
The sea lamprey makes for an interesting genetic case from an evolutionary standpoint, being a jawless vertebrate that diverged from jawed vertebrates millions of years ago.
“The sea lamprey is a primitive jawless vertebrate that diverged from other jawed vertebrates early in the vertebrate ancestry,” said co-author David McCauley, from Oklahoma University, in a statement. “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.”
McCauley explained that vertebrates have multiple copies of many genes in their genome as the result of two ℠whole-genome´ rounds of genetic duplication.
“One outstanding question has been the timing of these duplications in vertebrate history,” he said. “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.”
The OU geneticist added that the lamprey´s unique neural physiology makes for an interesting genomic and evolutionary study.
“Most vertebrates contain an insulating layer of cells that surround nerve cells,” he said. “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 said the neurons within lampreys are ℠unwrapped,´ suggesting that the insulation is specific to jawed vertebrates.
“Somewhat surprisingly, the sea lamprey genome contains multiple proteins involved in the synthesis of myelin, including its basic protein,” he noted. “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,” McCauley added.
In their report, the international team said that the sequencing answers some questions about the evolutionary spilt of jawless vertebrates; however many aspects of the divergence remain unanswered.
“Questions remain about the timing and subsequent elaboration of ancient genome duplication events and the elucidation of genetic innovations that may have contributed to the evolution and development of modern vertebrate features, including jaws, myelinated nerve sheaths, an adaptive immune system and paired appendages or limbs,” they said.
Sea lampreys can be found in the northern Atlantic Ocean, the Mediterranean Sea, and the Great Lakes, where they are considered an invasive species. The fish was first noticed in Lake Ontario in the 1830s just after the opening of the Erie Canal. Lampreys spread throughout the Great Lakes where their parasitic activity decimated the indigenous fish population.