cDNA-based gene mapping and GC3 profiling in the soft-shelled turtle suggest a chromosomal size-dependent GC bias shared by sauropsids |
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Authors: | Shigehiro Kuraku Junko Ishijima Chizuko Nishida-Umehara Kiyokazu Agata Shigeru Kuratani Yoichi Matsuda |
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Institution: | (1) Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku Kobe, 650-0047, Japan;(2) Laboratory of Animal Cytogenetics, Division of Genome Dynamics, Creative Research Initiative “Sousei”, Hokkaido University, North 10 West 8, Kita-ku Sapporo, 060-0810, Japan;(3) Division of Biological Sciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan;(4) Laboratory for Evolutionary Regeneration Biology, RIKEN Center for Developmental Biology, 2-2-3 Minatojima-minamimachi, Chuo-ku Kobe, 650-0047, Japan;(5) Present address: Laboratory for Molecular Developmental Biology, Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan |
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Abstract: | Mammalian and avian genomes comprise several classes of chromosomal segments that vary dramatically in GC-content. Especially
in chicken, microchromosomes exhibit a higher GC-content and a higher gene density than macrochromosomes. To understand the
evolutionary history of the intra-genome GC heterogeneity in amniotes, it is necessary to examine the equivalence of this
GC heterogeneity at the nucleotide level between these animals including reptiles, from which birds diverged. We isolated
cDNAs for 39 protein-coding genes from the Chinese soft-shelled turtle, Pelodiscus sinensis, and performed chromosome mapping of 31 genes. The GC-content of exonic third positions (GC3) of P. sinensis genes showed a heterogeneous distribution, and exhibited a significant positive correlation with that of chicken and human
orthologs, indicating that the last common ancestor of extant amniotes had already established a GC-compartmentalized genomic
structure. Furthermore, chromosome mapping in P. sinensis revealed that microchromosomes tend to contain more GC-rich genes than GC-poor genes, as in chicken. These results illustrate
two modes of genome evolution in amniotes: mammals elaborated the genomic configuration in which GC-rich and GC-poor regions
coexist in individual chromosomes, whereas sauropsids (reptiles and birds) refined the chromosomal size-dependent GC compartmentalization
in which GC-rich genomic fractions tend to be confined to microchromosomes. |
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Keywords: | GC-content microchromosome sauropsida turtle |
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