What question did this study set out to answer?

The research aims to explore the function and evolutionary significance of kisspeptin-type neuropeptides in echinoderms.

February 20, 2026Open Access

Evolution of neurohormone function revealed by actions of kisspeptin-type peptides in an echinoderm

Key Points

The research aims to explore the function and evolutionary significance of kisspeptin-type neuropeptides in echinoderms.
Analyzed kisspeptin precursor proteins in Asterias rubens
Utilized mRNA in situ hybridization and immunohistochemistry for expression patterns
Conducted in vitro experiments on gonad and stomach preparations
Performed in vivo injections to observe physiological effects
Identified two precursor proteins producing four kisspeptin-type neuropeptides
KP1-type neuropeptides exhibit myoinhibitory effects, while KP2-type are myoexcitatory
In vivo injections resulted in stomach eversion and influenced righting behavior
Phylogenetic analysis suggests unique inhibitory signaling in echinoderms or a loss in chordates

Abstract

Abstract Background The neurohormone kisspeptin regulates reproductive maturation and function in mammals by stimulating hypothalamic production and release of gonadotropin-releasing hormone. However, little is known about kisspeptin-type neuropeptide function in invertebrates and the evolution of kisspeptin signalling as a regulator of physiological processes. Here, we address these issues in a deuterostome invertebrate — the starfish Asterias rubens (phylum Echinodermata). Results Unlike mammals that have one kisspeptin precursor protein, in A. rubens , two precursor proteins (ArKPP1, ArKPP2) give rise to four kisspeptin-type neuropeptides (ArKP1.1, ArKP1.2, ArKP2.1, ArKP2.2). Use of mRNA in situ hybridisation and immunohistochemistry revealed widespread but different patterns of expression of KP1-type and KP2-type neuropeptides in the central nervous system, locomotory organs, sensory organs, reproductive system, and digestive system of A. rubens . In vitro experiments revealed that KP1-type and KP2-type neuropeptides have opposing myoinhibitory and myoexcitatory effects, respectively, on starfish gonad and stomach preparations. When injected in vivo, both KP1-type and KP2-type neuropeptides trigger stomach eversion and ArKP1.2 affects righting behaviour. Conclusions This study has revealed that kisspeptin-type neuropeptides are evolutionarily ancient and pleiotropic regulators of processes that extend beyond reproductive physiology. Furthermore, the excitatory actions of ArKP2.2 in A. rubens are consistent with stimulatory effects of kisspeptins in vertebrates; accordingly, ArKP2.2 acts as a ligand for a receptor (ArKPR3) that is closely related to vertebrate kisspeptin receptors. On the other hand, phylogenetic analysis of receptors for ArKP1.1 and ArKP1.2 indicates that inhibitory kisspeptin signalling either evolved uniquely in Ambulacraria (echinoderms, hemichordates) or originated in Urbilateria but was lost in chordates.

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