Cone visual pigments are present in gecko rod cells

Area of Science:

• Vision Science
• Molecular Biology
• Evolutionary Biology

Background:

• The Tokay gecko (Gekko gekko), a nocturnal lizard, exhibits unique visual pigments.
• Photoreceptor cells in lizards display pure-rod morphology.
• Biochemical analysis reveals P521 and P467 resemble iodopsin and rhodopsin, respectively.

Purpose of the Study:

• To investigate the molecular characteristics of Tokay gecko visual pigments.
• To compare the amino acid sequences of P521 and P467 with known visual pigments.
• To evaluate the evolutionary relationship between photoreceptor morphology and visual pigment sequences.

Main Methods:

• Deduction of amino acid sequences from cDNA for P521.
• Biochemical characterization of P467 and P521.
• Homology analysis comparing gecko visual pigments with avian and other vertebrate visual pigments.

Main Results:

• The deduced amino acid sequence of P521 shows high similarity to chicken iodopsin (a cone pigment).
• P467 exhibits the highest homology with chicken green-sensitive cone visual pigment, but also significant homology with rhodopsins (rod pigments).
• Amino acid sequences of visual pigments appear more conserved during evolution than photoreceptor cell morphology.

Conclusions:

• The findings support Walls' transmutation theory, suggesting lizard rod photoreceptors evolved from ancestral cone-like structures.
• Visual pigment molecular evolution may proceed independently of, and at a different rate than, photoreceptor cell morphological evolution.
• This study provides molecular evidence for the evolutionary plasticity of photoreceptor systems in vertebrates.