Characterisation of the mantle transcriptome and biomineralisation genes in the blunt-gaper clam, Mya truncata

Victoria A Sleight,Michael A.S Thorne,Lloyd S Peck,Jaison Arivalagan,Sophie Berland,Arul Marie,Melody S Clark

doi:10.1016/j.margen.2016.01.003

Abstract

Members of the Myidae family are ecologically and economically important, but there is currently very little molecular data on these species. The present study sequenced and assembled the mantle transcriptome of Mya truncata from the North West coast of Scotland and identified candidate biomineralisation genes. RNA-Seq reads were assembled to create 20,106 contigs in a de novo transciptome, 18.81% of which were assigned putative functions using BLAST sequence similarity searching (cuttoff E-value 1E−10). The most highly expressed genes were compared to the Antarctic clam (Laternula elliptica) and showed that many of the dominant biological functions (muscle contraction, energy production, biomineralisation) in the mantle were conserved. There were however, differences in the constitutive expression of heat shock proteins, which were possibly due to the M. truncata sampling location being at a relatively low latitude, and hence relatively warm, in terms of the global distribution of the species. Phylogenetic analyses of the Tyrosinase proteins from M. truncata showed a gene expansion which was absent in L. elliptica. The tissue distribution expression patterns of putative biomineralisation genes were investigated using quantitative PCR, all genes showed a mantle specific expression pattern supporting their hypothesised role in shell secretion. The present study provides some preliminary insights into how clams from different environments – temperate versus polar – build their shells. In addition, the transcriptome data provides a valuable resource for future comparative studies investigating biomineralisation.

Highlights

Biomineralisation is an essential biological process for many living organisms
The objectives of the present study were: 1.) Develop a molecular resource to aid the study of biomineralisation in M. truncata by sequencing, assembling and putatively annotating its mantle transcriptome. 2.) Identify and further characterise candidate biomineralisation genes in the newly-assembled M. truncata mantle transcriptome. 3.) Further characterise possible biomineralisation mechanisms in M. truncata by preliminary comparison with another bivalve species living at lower temperatures, the Antarctic clam, Laternula elliptica
RNA-Seq reads from the mantle tissue of nine animals were assembled to create 20,106 contigs in the final de novo transcriptome. 18.81% of contigs were assigned putative functions using Basic Local Alignment Search Tool (BLAST) sequence similarity searching

Summary

Introduction

Multiple taxa – in at least 30 phyla – secrete calcium carbonate crystals onto a protein matrix (Addadi and Weiner, 1997). Shells contain approximately 95–99% calcium carbonate (CaCO3) and 1–5% organic matrix; the organic component is a protein matrix which applies synergetic forces that either nucleate or inhibit crystal growth (Marie et al, 2010; Meenakshi et al, 1971; Weiner and Hood, 1975). The protein matrix is secreted by the mantle and recently, since the 'omics era began, much research has focussed on understanding the molecular mechanisms of shell growth — the genetic control of shell matrix protein secretion (Clark et al, 2010; Werner et al, 2013; Zhang et al, 2012)

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