A new fish-specific gene evolves new functions in cichlid fishes

Genes whose dysfunction does not affect normal survival are common. Are they only meaningless residues during evolution? Here, we identified a new fish-specific gene, which we named lg. Gene knockout resulted in no obvious phenotype in zebrafish, but lg evolved an amino acid mutation that was under positive selection in the modern haplochromine (MH) cichlid fish lineage, the well-known adaptive radiative lineage. Moreover, the cichlid fish-specific upstream region of lg drove new eGFP expression in tissues related to adaptation. Noticeably, this homologous region from different cichlid fishes drove different patterns, which is simply due to three MH-segregated SNP mutations that are predicted to bind a hormone-related transcription factor. We thus revealed an initially redundant gene evolving new functions in an adaptive radiative lineage. This further illuminates the mechanism of the emergence of new gene functions with respect to evo-devo in a broad way.