Genome evolution in the allotetraploid frog Xenopus laevis
Adam M. Session, Yoshinobu Uno, Taejoon Kwon, Jarrod A. Chapman, Atsushi Toyoda, Shuji Takahashi, Akimasa Fukui, Akira Hikosaka, Atsushi Suzuki, Mariko Kondo, Simon J. van Heeringen, Ian Quigley, Sven Heinz, Hajime Ogino, Haruki Ochi, Uffe Hellsten, Jessica B. Lyons, Oleg Simakov, Nicholas Putnam, Jonathan Stites, Yoko Kuroki, Toshiaki Tanaka, Tatsuo Michiue, Minoru Watanabe, Ozren Bogdanovic et al.
Nature 538, 336–343 (20 October 2016) doi:10.1038/nature19840
Received 25 December 2015 Accepted 09 September 2016 Published online 19 October 2016
X. laevis (on top) Photo credit: Atsushi Suzuki, Hiroshima University
To explore the origins and consequences of tetraploidy in the African clawed frog, we sequenced the Xenopus laevis genome and compared it to the related diploid X. tropicalis genome. We characterize the allotetraploid origin of X. laevis by partitioning its genome into two homoeologous subgenomes, marked by distinct families of ‘fossil’ transposable elements. On the basis of the activity of these elements and the age of hundreds of unitary pseudogenes, we estimate that the two diploid progenitor species diverged around 34 million years ago (Ma) and combined to form an allotetraploid around 17–18 Ma. More than 56% of all genes were retained in two homoeologous copies. Protein function, gene expression, and the amount of conserved flanking sequence all correlate with retention rates. The subgenomes have evolved asymmetrically, with one chromosome set more often preserving the ancestral state and the other experiencing more gene loss, deletion, rearrangement, and reduced gene expression.
Subject terms: Molecular evolution Genome evolution