A Bivalve Biomineralization Toolbox

Abstract

Mollusc shells are a result of the deposition of crystalline and amorphous calcite catalysed by enzymes and shell matrix proteins. Developing a detailed understanding of bivalve mollusc biomineralization pathways is complicated not only by the multiplicity of shell forms and microstructures in this class, but also by the evolution of associated proteins by domain co-option and domain shuffling. In spite of this, a minimal biomineralization toolbox comprising proteins and protein domains critical for shell production across species has been identified. Using a matched pair design to reduce experimental noise from inter-individual variation, combined with damage-repair experiments and a database of biomineralization shell matrix proteins (SMP) derived from published works, proteins were identified that are likely to be involved in shell calcification. Eighteen new, shared proteins likely to be involved in the processes related to the calcification of shells were identified by analysis of genes expressed during repair in Crassostrea gigas, Mytilus edulis and Pecten maximus. Genes involved in ion transport were also identified as potentially involved in calcification either via the maintenance of cell acid-base balance or transport of critical ions to the extrapallial space, the site of shell assembly. These data expand the number of candidate biomineralization proteins in bivalve molluscs for future functional studies and define a minimal functional protein domain set required to produce solid microstructures from soluble calcium carbonate. This is important for understanding molluscan shell evolution, the likely impacts of environmental change on biomineralization processes, materials science, and biomimicry research.

A New Gene Family Diagnostic for Intracellular Biomineralization of Amorphous Ca Carbonates by Cyanobacteria

“…The formation of mineral phases by living organisms is widespread in both eukaryotes and prokaryotes ( Weiner and Dove 2003 ). Although many cases of biomineralization in eukaryotes involve specific genes ( Marron et al 2016 ; Wang et al 2021 ; Yarra et al 2021 ), there is presently only one documented case of genetically controlled biomineralization in bacteria: the intracellular magnetite formation by magnetotactic bacteria ( Lefevre and Bazylinski 2013 ). The formation of Ca carbonates by cyanobacteria has been studied for several decades and cyanobacteria are thought to have been among the main calcifiers at the Earth surface since their appearance several billion years ago ( Altermann et al 2006 ).…”

Transcriptomic, Proteomic, and Functional Assays Underline the Dual Role of Extrapallial Hemocytes in Immunity and Biomineralization in the Hard Clam Mercenaria mercenaria

“…Bicarbonate transporters can supply dissolved inorganic carbon at the site of calcification and regulate pH (44). Yarra et al (45) investigated the transcriptomes of Pecten maximus (great scallop), C. gigas, and Mytulis edulis (blue mussel) during shell repair and proposed the upregulation of bicarbonate transporters was to regulate the availability of bicarbonate ions to the site of calcification. Genes overexpressed in the EPF transcriptome that could potentially be involved in calcification by transporting ions included ion transporters, solute carriers, and bicarbonate exchange genes.…”

“…In fact, complement proteins can function as pattern recognition receptors to identify pathogens and can initiate innate immune response ( 50 – 52 ). In particular, the calcium-dependent lectin-like C1qDC proteins display a marked expansion in bivalve mollusks [primarily to enable a tailored immune response to various microbes; ( 14 , 53 )] and have been strongly suggested to be involved in biomineralization as their expression increase after shell damage ( 45 ). A similar role for C1qDC in biomineralization has also been suggested in zebrafish ( 54 ).…”

A Chitin-Binding Protein Ultra-highly expressed in the Outer Fold of Mantle is Related to Shell Colour in Pacific Oyster Crassostrea gigas

“…3g). The mantle edge is the main organ that forms the shell periostraca 18, 32, 34 , and the CgCBP gene is only expressed in the outer fold of the mantle edge in C. gigas (Fig. 2d).…”

“…Mantle plays an important role in shell biological mineralisation [38][39][40] and is mainly divided into central mantle and mantle edge. The central mantle is involved in the calcification and thickening of the shell, such as inhibiting CaCO3 crystal and regulating the growth of epithelial cells and Ca 2+ ; the mantle edge contains a large number of conchiolin proteins prompting the shell to grow outward and participating in shell periostraca formation 18,39,41,42 . Shell colour is also correlated with the colour of the mantle edge 13,22,43,44 contains a large number of genes and genetic locus related to shell colour 8,[45][46][47][48] .…”