Abstract
The evolution of peptidergic signaling has been accompanied by a significant degree of ligand-receptor coevolution. Closely related clusters of peptide signaling molecules are observed to activate related groups of receptors, implying that genes encoding these ligands may orchestrate an array of functions, a phenomenon known as pleiotropy. Here we examine whether pleiotropic actions of peptide genes might influence ligand-receptor coevolution. Four test groups of neuropeptides characterized by conserved C-terminal amino acid sequence motifs and their cognate receptors were examined in the red flour beetle (Tribolium castaneum): 1) cardioacceleratory peptide 2b (CAPA); CAPAr, 2) pyrokinin/diapause hormone (PK1/DH); PKr-A, -B, 3) pyrokinin/pheromone biosynthesis activating hormone (PK2/PBAN); PKr-C, and 4) ecdysis triggering hormone (ETH); ETHr-b. Ligand-receptor specificities were established through heterologous expression of receptors in cell-based assays for 9 endogenous ligands. Based on ligand-receptor specificity analysis, we found positive pleiotropism exhibited by ETH on ETHR-b and CAPAr, whereas PK1/DH and CAPA are more highly selective for their respective authentic receptors than would be predicted by phylogenetic analysis. Disparities between evolutionary trees deduced from receptor sequences vs. functional ligand-receptor specificities lead to the conclusion that pleiotropy exhibited by peptide genes influences ligand-receptor coevolution.
Highlights
The evolution of peptidergic signaling has been accompanied by a significant degree of ligand-receptor coevolution
Four test groups of neuropeptides characterized by conserved C-terminal amino acid sequence motifs and their cognate receptors were examined in the red flour beetle (Tribolium castaneum): 1) cardioacceleratory peptide 2b (CAPA); CAPA receptor (CAPAr), 2) pyrokinin/diapause hormone (PK1/DH); PKr-A, -B, 3) pyrokinin/pheromone biosynthesis activating hormone (PK2/PBAN); PKr-C, and 4) ecdysis triggering hormone (ETH); ETHr-b
Based on ligand-receptor specificity analysis, we found positive pleiotropism exhibited by ETH on ETHR-b and CAPAr, whereas PK1/DH and CAPA are more highly selective for their respective authentic receptors than would be predicted by phylogenetic analysis
Summary
Hongbo Jiang[1,2], Zhaojun Wei[2], Ronald J. Stability of a newly evolved ligand-receptor signaling pathway may require its rapid sub- or neofunctionalization[3,4] for minimization of functional redundancy, for example through changes in spatial or temporal expression patterns Such a role for ligand-receptor coevolution in diversifying evolution is only one possible outcome. In the context of peptide signaling, a single peptide gene product signaling via distinct receptors may lead to multiple physiological and phenotypic outcomes Such pleiotropic peptide action could be an important evolutionary force. It may be time to recognize that evolution selects not just single ligand-receptor partners, but webs of interdigitating peptide signaling networks that orchestrate physiological states involving multiple organ systems and diverse functions. Our data support a role for pleiotropism in evolution of ligand-receptor interactions
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