The gastrin-releasing peptide/bombesin system revisited by a reverse-evolutionary study considering Xenopus

Hirotaka Sakamoto,Asuka Hirooka,Yukitoshi Katayama,Keiko Takanami,Yasuhisa Kobayashi,Takumi Oti,Mayuko Hamada,Tatsuya Sakamoto,Daiki Fujiyama

doi:10.1038/s41598-021-92528-x

Abstract

Bombesin is a putative antibacterial peptide isolated from the skin of the frog, Bombina bombina. Two related (bombesin-like) peptides, gastrin-releasing peptide (GRP) and neuromedin B (NMB) have been found in mammals. The history of GRP/bombesin discovery has caused little attention to be paid to the evolutionary relationship of GRP/bombesin and their receptors in vertebrates. We have classified the peptides and their receptors from the phylogenetic viewpoint using a newly established genetic database and bioinformatics. Here we show, by using a clawed frog (Xenopus tropicalis), that GRP is not a mammalian counterpart of bombesin and also that, whereas the GRP system is widely conserved among vertebrates, the NMB/bombesin system has diversified in certain lineages, in particular in frog species. To understand the derivation of GRP system in the ancestor of mammals, we have focused on the GRP system in Xenopus. Gene expression analyses combined with immunohistochemistry and Western blotting experiments demonstrated that GRP peptides and their receptors are distributed in the brain and stomach of Xenopus. We conclude that GRP peptides and their receptors have evolved from ancestral (GRP-like peptide) homologues to play multiple roles in both the gut and the brain as one of the ‘gut-brain peptide’ systems.

Highlights

The fourteen-amino acid peptide, bombesin, was initially described as a possible antibacterial peptide isolated from the skin of the European fire-bellied toad, Bombina bombina, and was shown to have potent bioactivity in the mammalian nervous system[1,2]
Peptide sequences of neuromedin B (NMB) are highly conserved among vertebrates, 11 amino acids in the carboxyl-terminus are identical between human, rat, chick, medaka, and zebrafish (Supplementary Fig. S1)
It has been reported that frogs have independent genes for both gastrin-releasing peptide (GRP) and bombesin, and this raises the possibility that mammals have an as yet uncharacterized gene encoding a true mammalian b ombesin[27]

Summary

Introduction

The fourteen-amino acid peptide, bombesin, was initially described as a possible antibacterial peptide isolated from the skin of the European fire-bellied toad, Bombina bombina, and was shown to have potent bioactivity in the mammalian nervous system[1,2]. Because GRP could reproduce most of the biological effects of bombesin in many mammals, GRP had long been considered as the mammalian equivalent of amphibian b ombesin[5,6,7]. Little information is currently available on the function of the GRP/GRPR system in the CNS, because GRP has long been considered as the mammalian equivalent of bombesin[5,6,7]. It has been reported that frogs synthesize both GRP and bombesin, which are genetically distinct peptides, suggesting that GRP is not mammalian bombesin[27]. Based on amino acid sequence, two of the classes were clearly the amphibian orthologous genes of the GRPR and NMBR, but not the BRS-328. To understand its derivation of GRP system from the ancestor of amniotes, we have focused on the GRP system that is widely conserved among vertebrates, and examined its expression in the anamniote clawed frog (Xenopus tropicalis) and contrasted it with bombesin, as amphibians represent an important place in the evolution of tetrapods and our understanding of bombesin and GRP

Methods

Results

Conclusion