AUTHOR=Kanda Shinji , Oka Yoshitaka 

TITLE=Evolutionary Insights into the Steroid Sensitive kiss1 and kiss2 Neurons in the Vertebrate Brain

JOURNAL=Frontiers in Endocrinology

VOLUME=3

YEAR=2012

URL=https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2012.00028

DOI=10.3389/fendo.2012.00028

ISSN=1664-2392

ABSTRACT=<p>Kisspeptin was originally found as a peptide product of <italic>Kiss1</italic> gene and is now supposed to be an essential central regulator of reproduction in mammals. However, there is now a growing body of evidence to suggest that <italic>kiss2</italic>, the paralogous gene for <italic>kiss1</italic>, evolved in parallel during vertebrate lineage, and the <italic>kiss2</italic> product also activates the GPR54 (kisspeptin receptor) signaling pathways. Therefore, it is now widely accepted that both <italic>kiss1</italic> and <italic>kiss2</italic> are the kisspeptin genes. Interestingly, either <italic>kiss1</italic> or <italic>kiss2</italic> or both have been lost during evolution in many vertebrate species, and the functional significance of <italic>kiss1</italic> or <italic>kiss2</italic> for the central regulation of reproduction is suggested to vary according to the species. Here, we argue that the steroid sensitivity of the <italic>kiss1</italic> or <italic>kiss2</italic> neurons has been well conserved during evolution among tetrapods and teleosts, and thus it may be the key to understanding the functional homologies of certain populations of kisspeptin (<italic>kiss1</italic> or <italic>kiss2</italic>) neurons among different species of vertebrates. In the present review, we will first introduce recent advances in the study of steroid sensitive <italic>kiss1</italic> and <italic>kiss2</italic> systems in vertebrates and effects of peptide administrations <italic>in vivo</italic>. By comparing the similarities and differences between <italic>kiss1</italic> and <italic>kiss2</italic> of neuronal localization and sensitivity to gonadal steroids in various tetrapods and teleosts, we discuss the evolution of kisspeptin neuronal systems after gene duplication of ancestral kisspeptin genes to give rise to <italic>kiss1</italic> and <italic>kiss2</italic>.</p>