Identification, evolution and expression of an insulin-like peptide in the cephalochordate Branchiostoma lanceolatum.

Claire Lecroisey,Vincent Laudet,Yann Le Pétillon,Eckhard Lammert,Hector Escriva

doi:10.1371/journal.pone.0119461

Abstract

Insulin is one of the most studied proteins since it is central to the regulation of carbohydrate and fat metabolism in vertebrates and its expression and release are disturbed in diabetes, the most frequent human metabolic disease worldwide. However, the evolution of the function of the insulin protein family is still unclear. In this study, we present a phylogenetic and developmental analysis of the Insulin Like Peptide (ILP) in the cephalochordate amphioxus. We identified an ILP in the European amphioxus Branchiostoma lanceolatum that displays structural characteristics of both vertebrate insulin and Insulin-like Growth Factors (IGFs). Our phylogenetic analysis revealed that amphioxus ILP represents the sister group of both vertebrate insulin and IGF proteins. We also characterized both temporal and spatial expression of ILP in amphioxus. We show that ilp is highly expressed in endoderm and paraxial mesoderm during development, and mainly expressed in the gut of both the developing embryo and adult. We hypothesize that ILP has critical implications in both developmental processes and metabolism and could display IGF- and insulin-like functions in amphioxus supporting the idea of a common ancestral protein.

Highlights

Proteins of the insulin-relaxin superfamily are implicated in critical physiological processes like metabolism, growth control, reproduction, cardiovascular function, and longevity in a wide range of animals
The amphioxus Insulin Like Peptide (ILP) is closely related to both insulin and insulin-like growth factors (IGFs) from vertebrates The ILP protein sequence from B. californiensis was used as a template for in silico identification of the B. lanceolatum ilp using the reference transcriptome [19]
B. lanceolatum ILP shows 88,8% sequence identity with ILP from B. californiensis, 90,8% sequence identity with ILP sequence from B. belcheri and 84,1% sequence identity with sequence ID 121099 from B. floridae genome, but only 26,9%, 17,1%, 15,7%, 12,2% and 8,1% sequence identity with the 5 others sequences from B. floridae genome [16]

Summary

Introduction

Proteins of the insulin-relaxin superfamily are implicated in critical physiological processes like metabolism, growth control, reproduction, cardiovascular function, and longevity in a wide range of animals. Two sequences have been identified in the ascidian Chelyosoma productum as members of the insulin-relaxin superfamily on the basis of sequence and expression analysis Their phylogenetic positions has not been solved because of their high divergence and it has been speculated that these genes are the result of a recent lineage-specific gene duplication [4]. The sequencing of the B. floridae genome revealed 6 putative members of the insulin-relaxin superfamily [16] Analyses of these sequences revealed that two of them (protein IDs 121099 and 77763) are related to the insulin/IGF subfamily [17], but the phylogenetic positions of the other four sequences have not been investigated. We analysed the phylogenetic relationship between all the insulin-like sequences that have been previously identified in amphioxus and their relationship with other proteins from the insulin-relaxin superfamily in chordates. We show by qPCR that ilp is highly expressed in the gut in the adult amphioxus

Results and Discussion

Conclusion

Experimental Procedures Cloning