Diversification processes of teleost intron-less opsin genes

Area of Science:

• Evolutionary biology
• Molecular genetics
• Biochemistry

Background:

• Opsins are crucial photosensitive proteins in vertebrates, mediating visual and non-visual photoreception.
• Most opsin genes contain introns, but teleosts possess intron-less opsin genes, likely originating from retroduplication.
• The Opn4 (melanopsin) gene, involved in non-image-forming photoreception, is a focus due to its unique intron-less form in teleosts.

Purpose of the Study:

• To investigate the evolutionary history of Opn4 genes in teleost and non-teleost fishes.
• To determine the origin and functional significance of the intron-less Opn4 gene in teleosts.
• To elucidate the contribution of Opn4 retrogenes to opsin repertoire diversification and adaptation.

Main Methods:

• Comparative gene structure analysis of Opn4 genes across various fish species.
• Synteny analysis to trace the emergence of intron-less Opn4 genes.
• Biochemical and histochemical analyses to assess the function and expression of Opn4 proteins.

Main Results:

• The intron-less Opn4 gene originated via retroduplication after the divergence of the bichir lineage.
• In teleosts, the new intron-less Opn4 gene was readily adopted and widely expressed without significant protein alteration.
• The evolutionary trajectory of Opn4 retrogenes mirrors that of rhodopsin retrogenes in Actinopterygii.

Conclusions:

• The acquisition of intron-less Opn4 (melanopsin) genes through retroduplication is a key event in teleost evolution.
• This process contributed to the expansion of opsin gene families and adaptation to diverse aquatic environments.
• The findings provide insights into the mechanisms driving gene duplication and functional innovation in vertebrates.