Transcriptome analysis of shell color-related genes in the hard clam Mercenaria mercenaria.

The shell color of marine bivalves shows great diversity and is considered as an economic trait. In China, the hard clam, Mercenaria mercenaria, commonly has three shell colors in the wild: red, white, and mottled. The genetic mechanisms controlling color segregation are not fully understood. In this study, RNA-seq was performed to exploit the related shell color genes and determine the genetic basis of the different shell colors. Nine sequence libraries with those three shell colors of hard clam were constructed; 406,377 transcripts and 248,251 unigenes were obtained with N50 values of 1365 and 1682 base pairs, respectively. Cluster analysis identified 363, 392, and 220 genes exclusively highly expressed in red, white, and mottled clams, respectively. We further classified differentially expressed genes (DEGs), the genes involved in lipid binding and transport, signal transduction, ATP synthesis, and other processes in the red vs white comparison were found, which may participate in red shell formation. DEGs related to signal transduction, particularly G protein-coupled receptor activity, were found in the red vs mottled comparison, suggesting that these genes might be important in mottled shell formation. In the white vs mottled comparison, DEGs involved in zinc ion binding were found. Our results provide new insights into shell color formation mechanisms in molluscs. This information could be used in selective breeding and marker-assisted breeding of this economically important clam species.

Strontium doped hydroxyapatite from Mercenaria clam shells: Synthesis, mechanical and bioactivity study.

Synthesis of strontium-doped hydroxyapatite from Mercenaria clam shells has been carried out by hydrothermal method. The doping of bioceramic, processed from biogenic resources is mostly unexplored. The objective is to understand the effect of strontium (Sr) incorporation on phase stability, sintering behaviour, mechanical properties and cytotoxicity of hydroxyapatite (HAp) derived from clam shells. The different molar concentrations of Sr, varies from 10, 30, 50, 70% of Ca, were substituted into the HAp. The synthesized powders were sintered at 1200 °C in air. The as synthesized powders and sintered specimens were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy. The crystallite size and cell parameters of sintered specimens were analyzed from XRD. The XRD of hydrothermally synthesized powders mostly matched with HAp with slight shifting due to Sr doping. However, some distinct Sr based compounds were also observed where Sr substitution is more that 50% of Ca. The XRD of sintered specimen showed increasing ß-tricalcium phosphate (ß-TCP) phase with Sr substitution. The sintered density of solid samples gradually increased from 3.04 g/cc to 3.50 g/cc and surface energy decreased with increasing Sr substitution. Similarly, microhardness, fracture toughness and nanohardness of solid samples found to be enhanced with Sr substitution. The elastic modulus gradually increased from 130 to 137 GPa for HAp and Sr substituted HAp (70% of Ca). The in vitro cytotoxicity of sintered specimen against mouse osteoblast cell line showed that all the samples were nontoxic. However cell proliferation found low for the solid samples containing more than 50% Sr substitution.