Fig. 8

Phylogenetic tree summarizing the evolution of the PDE6 genes in vertebrates. The figure illustrates the expansion of the PDE6 catalytic (left columns) and inhibitory (right columns) gene families during vertebrate evolution and shows the approximate divergence times of species included in the analyses. No representative for any of these gene families were found in Amphioxus. The ancestral PDE6 catalytic subunit gene appeared in the common ancestor of tunicates (represented by a sea squirt) and vertebrates. On the contrary, the ancestral PDE6 inhibitory subunit gene appeared in the common ancestor of all vertebrates, after the split from tunicates. Both gene families expanded in 2R and were subsequently subjected to losses resulting in triplets for the catalytic (PDE6A, PDE6B and PDE6C) and the inhibitory subunit genes (PDE6G, PDE6H and PDE6I). In the sea lamprey, additional losses occurred resulting in one catalytic subunit gene and two inhibitory subunit genes. Similarly, one inhibitory subunit gene (PDE6I) was lost in cartilaginous fish (represented by the Elephant shark) and amniotes (represented by the grey short-tailed opossum, human, mouse, green anole lizard and chicken). In non-amniote lobe-finned fish (represented by the western clawed frog and the coelacanth) and ray-finned fish (represented by the spotted gar and all teleosts), all three PDE6 catalytic and three PDE6 inhibitory subunit genes are preserved. Teleost fish retained extra duplicates for some of the inhibitory subunit genes after 3R, as well as from local duplications. Finally, PDE6A was lost in the lineage leading to birds and non-avian reptiles. For consistency purposes, the colour code for the gene boxes is the same as used in Figs. 1, 2, Additional file 3: Figures S1-S17. Empty white boxes means that the orthology assignment could not be done confidently and boxes with an asterisk indicates fragmented sequences