Origin of amphibian and avian chromosomes by fission, fusion, and retention of ancestral chromosomes

Origin of amphibian and avian chromosomes by fission, fusion, and retention of ancestral chromosomes

Amphibian genomes differ greatly in DNA content and chromosome size, morphology, and number. Investigations of this diversity are needed to identify mechanisms that have shaped the evolution of vertebrate genomes. We used comparative mapping to investigate the organization of genes in the Mexican ax...

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Bibliographic Details
Published in:Genome research Vol. 21; no. 8; pp. 1306 - 1312
Main Authors: Voss, Stephen R, Kump, D Kevin, Putta, Srikrishna, Pauly, Nathan, Reynolds, Anna, Henry, Rema J, Basa, Saritha, Walker, John A, Smith, Jeramiah J
Format: Journal Article
Language:English
Published: United States Cold Spring Harbor Laboratory Press 01-08-2011
Subjects:
Ambystoma
Ambystoma - genetics
Ambystoma mexicanum
Amphibians - genetics
Animals
Anura
Birds - genetics
Caudata
Chickens - genetics
Chromosome Mapping
Chromosomes - genetics
Evolution, Molecular
Genetic Linkage
Humans
Xenopus
Xenopus - genetics
Xenopus tropicalis
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Summary:Amphibian genomes differ greatly in DNA content and chromosome size, morphology, and number. Investigations of this diversity are needed to identify mechanisms that have shaped the evolution of vertebrate genomes. We used comparative mapping to investigate the organization of genes in the Mexican axolotl (Ambystoma mexicanum), a species that presents relatively few chromosomes (n = 14) and a gigantic genome (>20 pg/N). We show extensive conservation of synteny between Ambystoma, chicken, and human, and a positive correlation between the length of conserved segments and genome size. Ambystoma segments are estimated to be four to 51 times longer than homologous human and chicken segments. Strikingly, genes demarking the structures of 28 chicken chromosomes are ordered among linkage groups defining the Ambystoma genome, and we show that these same chromosomal segments are also conserved in a distantly related anuran amphibian (Xenopus tropicalis). Using linkage relationships from the amphibian maps, we predict that three chicken chromosomes originated by fusion, nine to 14 originated by fission, and 12-17 evolved directly from ancestral tetrapod chromosomes. We further show that some ancestral segments were fused prior to the divergence of salamanders and anurans, while others fused independently and randomly as chromosome numbers were reduced in lineages leading to Ambystoma and Xenopus. The maintenance of gene order relationships between chromosomal segments that have greatly expanded and contracted in salamander and chicken genomes, respectively, suggests selection to maintain synteny relationships and/or extremely low rates of chromosomal rearrangement. Overall, the results demonstrate the value of data from diverse, amphibian genomes in studies of vertebrate genome evolution.
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ISSN:1088-9051
1549-5469
DOI:10.1101/gr.116491.110