How opsins diversified after the teleost whole-genome duplication: Insights from two parietopsins of the red piranha, Pygocentrus nattereri

The teleost whole-genome duplication (TGD) contributed to functional diversification of opsins. Some TGD paralogs, including those of parapinopsin (PP), Vertebrate Ancient (VA) opsin, and long wavelength-sensitive (LWS) opsin, show different absorption spectra and/or expression patterns. However, our knowledge of detailed evolutionary processes and mechanisms by which TGD contributed to opsin diversification is still limited. Here, we report that TGD paralogs of parietopsin (PT1 and PT2) are retained in extant species. While most species, including the zebrafish, have only PT1, several characins, including the red piranha ( Pygocentrus nattereri ), retain both PT1 and PT2. The Mexican tetra ( Astyanax mexicanus ) and catfishes have only PT2. To assess the degree of functional diversification between PT1 and PT2, we characterized spectral properties and expression patterns. Maximum absorption spectra differ slightly among PTs. Those of red piranha PT1, PT2, Mexican tetra PT2, and Japanese catfish ( Silurus asotus ) PT2 were located at 517 nm, 528 nm, 517 nm, and ∼535 nm, respectively. Fluorescence in situ hybridization showed that (1) piranha PT1 and PT2 are expressed in the same pineal cells, and (2) they are also co-expressed with PP1 . Based on these findings, functional diversification of opsins after gene duplication is discussed.