ABSTRACT
The African clawed frog, Xenopus laevis, has been used as a model animal since the 1930s to study various subjects by biochemical and molecular biological approaches. X. laevis has advantages as a model animal, some of which may be owing to X. laevis being allotetraploid. However, gene redundancy due to allotetraploidy was recognized as a disadvantage since the late 1990s, when developmental genetics dominated the field of developmental biology. The size and complexity of this genome were also disadvantages for whole genome analysis. In 2016, thanks to improved technologies and reduction of costs for sequencing and to the inbred strain J, the entire genome structure as well as subgenomes, called L and S, of X. laevis were revealed. Detailed analyses of gene organization in the subgenomes, such as retention rates of homeolog pairs and paralogous gene expansions, including the rDNA cluster, demonstrated asymmetric evolution of subgenomes, in which L is more conserved than the S genome. Since then, allotetraploid genome analyses have opened a new research field in animals by shedding light on subgenome evolution after allopolyploidization, which may also provide insights into what happened in the two rounds of whole genome duplication (WGD) during vertebrate evolution, as well as in the third round of WGD in the common ancestor of teleosts. We will discuss the historical background of genome studies of Xenopus laevis, its contributions to science, and future directions.
