Genome Biology of the Cyclostomes and Insights into the Evolutionary Biology of Vertebrate Genomes

May 12, 2011Integrative and comparative biology

Genome biology of jawless fish and what it reveals about vertebrate genome evolution

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Abstract

The genomes of lamprey and hagfish exhibit a capacity for rearrangement that exceeds what is known from jawed vertebrates.

Lamprey and hagfish undergo rearrangement of adaptive immune receptors, which evolved independently from jawed vertebrates.
Extensive programmed rearrangements of the genome occur in lamprey and hagfish during embryonic development.
The evolutionary history of vertebrate genomes may involve deep shared ancestry and rapid divergence among lampreys, hagfish, and jawed vertebrates.
Two versions of programmed rearrangement in lamprey and hagfish could date back to an ancestral lineage over 400 million years ago.

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The jawless vertebrates (lamprey and hagfish) are the closest extant outgroups to all jawed vertebrates (gnathostomes) and can therefore provide critical insight into the evolution and basic biology of vertebrate genomes. As such, it is notable that the genomes of lamprey and hagfish possess a capacity for rearrangement that is beyond anything known from the gnathostomes. Like the jawed vertebrates, lamprey and hagfish undergo rearrangement of adaptive immune receptors. However, the receptors and the mechanisms for rearrangement that are utilized by jawless vertebrates clearly evolved independently of the gnathostome system. Unlike the jawed vertebrates, lamprey and hagfish also undergo extensive programmed rearrangements of the genome during embryonic development. By considering these fascinating genome biologies in the context of proposed (albeit contentious) phylogenetic relationships among lamprey, hagfish, and gnathostomes, we can begin to understand the evolutionary history of the vertebrate genome. Specifically, the deep shared ancestry and rapid divergence of lampreys, hagfish and gnathostomes is considered evidence that the two versions of programmed rearrangement present in lamprey and hagfish (embryonic and immune receptor) were present in an ancestral lineage that existed more than 400 million years ago and perhaps included the ancestor of the jawed vertebrates. Validating this premise will require better characterization of the genome sequence and mechanisms of rearrangement in lamprey and hagfish.

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Genome Biology of the Cyclostomes and Insights into the Evolutionary Biology of Vertebrate Genomes

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