The whole-genome sequence of the half-smooth tongue sole, the first flatfish to be sequenced, is reported in Nature Genetics. The work provides insights into the evolution of sex chromosomes.
The half-smooth tongue sole undergoes a transition from living in the open sea to seabed during which time the fish undergoes a metamorphosis as part of adaptation to the new environment, shifting from a symmetric to asymmetric body shape.
Songlin Chen and colleagues sequenced the genomes of a male (which has sex chromosomes ZZ) and a female (ZW) Chinese half-smooth tongue sole, Cynoglossus semilaevis. Their analyses provide a view into the structure and evolution of the tongue sole sex chromosomes Z and W and suggest that they evolved from a pair of autosomes (chromosomes that are not sex chromosomes). They also identify genes showing differential regulation between pre and post-metamorphosis fish, suggesting an involvement of these genes in adaptation to the seabed environment.