Figure 1.

Summary of the subtypes of ligand and receptor genes for kisspeptin systems in the genome along the vertebrate lineage. kiss1 and kiss2 are supposed to be duplicated before the emergence of lamprey, and probably due to the whole genome duplication of the ancestral vertebrate. It is supposed that kiss2 and gpr54-2 were lost in marsupial and placental mammals after the divergence from the monotreme during mammalian evolution. It should be noted that some teleost species have lost gpr54-1, but no teleosts have lost gpr54-2, suggesting the significance of gpr54-2 in teleosts, which is opposite to the case in the mammalian lineage. It is also consistent with the higher level of expression of gpr54-2 compared to that of gpr54-1 in teleost brains. The loss of kiss1 (blue) or kiss2 (red) is indicated by asterisks.