Structure, Synthesis, and Phylogeny of Kisspeptin and its Receptor - Kisspeptin Signaling in Reproductive Biology - page 7

Chapter 2
Structure, Synthesis, and Phylogeny
of Kisspeptin and its Receptor
Shinji Kanda and Yoshitaka Oka
Abstract The kisspeptin system is considered to be essential for successful
mammalian reproduction. In addition to the Kiss1 peptide, Kiss2, the product of
kiss2 (the kiss1 paralogue), has also been shown to activate kisspeptin receptor sig-
naling pathways in nonmammalian species. Furthermore, in nonmammalian spe-
cies, there are two subtypes of receptors, Gpr54-1 (known as GPR54 or Kiss1R in
mammals) and Gpr54-2. Although complete understanding of the two kisspeptin—
two kisspeptin receptor systems in vertebrates is not so simple, a careful examina-
tion of the phylogeny of their genes may provide insights into the functional
generality and differences among the kisspeptin systems in different animal phyla.
In this chapter, we fi rst discuss the structure of kisspeptin ligands, Kiss1 and Kiss2,
and their characteristics as physiologically active peptides. Then, we discuss the
evolutionary traits of kiss1 and kiss2 genes and their receptor genes, gpr54 - 1 and
gpr54 - 2 . It appears that each animal species has selected either kiss1 or kiss2 rather
randomly, leading us to propose that some of the important characteristics of kiss-
peptin neurons, such as steroid sensitivity and the anatomical relationship with the
hypophysiotropic GnRH1 neurons, may be the keys to understanding the general
functions of different kisspeptin neuronal populations throughout vertebrates.
Species differences in kiss1 / kiss2 may also provide insights into the evolutionary
mechanisms of paralogous gene-expressing neuronal systems. Finally, because kis-
speptins belong to one of the members of the RFamide peptide families, we discuss
the functional divergence of kisspeptins from the other RFamide peptides, which
may be explained from phylogenetic viewpoints.
S. Kanda, Ph.D ￿ Y. Oka , Ph.D. ( * )
Department of Biological Sciences, Graduate School of Science, University of Tokyo,
7-3-1 Hongo , Bunkyo , Tokyo 113-0033 , Japan
e-mail: [e-mail]