title: Inference of the protokaryotypes of amniotes and tetrapods and the evolutionary processes of microchromosomes from comparative gene mapping.
abstract: Comparative genome analysis of non-avian reptiles and amphibians provides important clues about the process of genome evolution in tetrapods. However, there is still only limited information available on the genome structures of these organisms. Consequently, the protokaryotypes of amniotes and tetrapods and the evolutionary processes of microchromosomes in tetrapods remain poorly understood. We constructed chromosome maps of functional genes for the Chinese soft-shelled turtle (Pelodiscus sinensis), the Siamese crocodile (Crocodylus siamensis), and the Western clawed frog (Xenopus tropicalis) and compared them with genome and/or chromosome maps of other tetrapod species (salamander, lizard, snake, chicken, and human). This is the first report on the protokaryotypes of amniotes and tetrapods and the evolutionary processes of microchromosomes inferred from comparative genomic analysis of vertebrates, which cover all major non-avian reptilian taxa (Squamata, Crocodilia, Testudines). The eight largest macrochromosomes of the turtle and chicken were equivalent, and 11 linkage groups had also remained intact in the crocodile. Linkage groups of the chicken macrochromosomes were also highly conserved in X. tropicalis, two squamates, and the salamander, but not in human. Chicken microchromosomal linkages were conserved in the squamates, which have fewer microchromosomes than chicken, and also in Xenopus and the salamander, which both lack microchromosomes; in the latter, the chicken microchromosomal segments have been integrated into macrochromosomes. Our present findings open up the possibility that the ancestral amniotes and tetrapods had at least 10 large genetic linkage groups and many microchromosomes, which corresponded to the chicken macro- and microchromosomes, respectively. The turtle and chicken might retain the microchromosomes of the amniote protokaryotype almost intact. The decrease in number and/or disappearance of microchromosomes by repeated chromosomal fusions probably occurred independently in the amphibian, squamate, crocodilian, and mammalian lineages.
authors.affiliation: Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan.
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Uno
authors.forename: Chizuko
authors.initials: C
authors.lastname: Nishida
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tarui
authors.forename: Satoshi
authors.initials: S
authors.lastname: Ishishita
authors.forename: Chiyo
authors.initials: C
authors.lastname: Takagi
authors.forename: Osamu
authors.initials: O
authors.lastname: Nishimura
authors.forename: Junko
authors.initials: J
authors.lastname: Ishijima
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Ota
authors.forename: Ayumi
authors.initials: A
authors.lastname: Kosaka
authors.forename: Kazumi
authors.initials: K
authors.lastname: Matsubara
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Murakami
authors.forename: Shigeru
authors.initials: S
authors.lastname: Kuratani
authors.forename: Naoto
authors.initials: N
authors.lastname: Ueno
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Agata
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Matsuda
mesh_terms: D000489:Alligators and Crocodiles / Q000235:genetics*; D000818:Animals; D002645:Chickens / Q000235:genetics; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D006801:Humans; D008116:Lizards / Q000235:genetics; D012911:Snakes / Q000235:genetics; D014426:Turtles / Q000235:genetics*; D014562:Caudata / Q000235:genetics; D014981:Xenopus / Q000235:genetics*