Troponin-I is present as an essential component of muscles in echinoderm larvae

Shunsuke Yaguchi,Junko Yaguchi,Hiroyuki Tanaka

doi:10.1038/srep43563

Shunsuke Yaguchi, Junko Yaguchi + Show 1 more

Open Access

https://doi.org/10.1038/srep43563

Copy DOI

Journal: Scientific Reports	Publication Date: Mar 8, 2017
Citations: 13	License type: open-access

Affiliation: University of Tsukuba, Hokkaido University

Abstract

The troponin complex, composed of Troponin-I, Troponin-T and Troponin-C, is an essential mediator of the contraction of striated muscle downstream of calcium signaling in almost all bilaterians. However, in echinoderms and hemichordates, collectively termed Ambulacraria, the components of the troponin complex have never been isolated, thus suggesting that these organisms lost the troponin system during evolution. Here, by analyzing genomic information from sea urchins, we identify the troponin-I gene and isolate its complete mRNA sequence. Using this information, we reveal that the larval muscles express this gene and its translated product and that the protein is definitely a functional molecule expressed in sea urchin larvae by showing that Troponin-I morphants are unable to swallow algae. We conclude that muscular contraction in all bilaterians universally depends on a regulatory system mediated by Troponin-I, which emerged in the common ancestor of bilaterians.

Highlights

The troponin complex, composed of Troponin-I, Troponin-T and Troponin-C, is an essential mediator of the contraction of striated muscle downstream of calcium signaling in almost all bilaterians
It has been reported that echinoderms and hemichordates, collectively termed Ambulacraria, lack all components of the troponin complex, which is composed of Troponin-I (TnI), Troponin-T (TnT), and Troponin-C (TnC), raising the question of how the troponin systems emerged in the ancestors of bilaterians and how they evolved in the deuterostomes[4,5,6]
By analyzing the genomes and transcriptomes of S. purpuratus[9,10] and Hemicentrotus pulcherrimus (Yaguchi S, unpublished), a candidate TnI gene was found in H. pulcherrimus (LC187281)

Summary

Introduction

The troponin complex, composed of Troponin-I, Troponin-T and Troponin-C, is an essential mediator of the contraction of striated muscle downstream of calcium signaling in almost all bilaterians. The isolation of the complete TnT from H. pulcherrimus is awaited, and biochemical analysis of HpTnI and HpTnT with and without CaM on muscular components would indicate how members of the sea urchin group use the troponin complex in regulating muscle contraction via Ca2+.

Results

Conclusion