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More molecular support for turtles as archosauromorphs



From: Ben Creisler
bcreisler@gmail.com


A new paper in PLoS ONE:

Chizuko Nishida, Hiroshi Tarui, Satoshi Ishishita, Chiyo Takagi, Osamu
Nishimura, Junko Ishijima, Hidetoshi Ota, Ayumi Kosaka, Kazumi
Matsubara, Yasunori Murakami, Shigeru Kuratani, Naoto Ueno, Kiyokazu
Agata & Yoichi Matsuda (2012)
Inference of the Protokaryotypes of Amniotes and Tetrapods and the
Evolutionary Processes of Microchromosomes from Comparative Gene
Mapping.
PLoS ONE 7(12): e53027.
doi:10.1371/journal.pone.0053027
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0053027



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.