Expression of bone morphogenetic protein 10 and its role in biomineralization in Hyriopsis cumingii.

Shells and pearls are the products of biomineralization of shellfish after ingesting external mineral ions. Bone morphogenetic proteins (BMPs) play a role in a variety of biological function, and the genes that encode them, are considered important shell-forming genes in mollusks and are associated with shell and pearl formation, embryonic development, and other functions, but bone morphogenetic protein 10 (BMP10) is poorly understood in Hyriopsis cumingii. In this study, we cloned Hc-BMP10 and obtained a 2477 bp full-length sequence encoding 460 amino acids with a conserved TGF-ß structural domain. During the embryonic developmental stages, the cleavage stage had the highest expression of Hc-BMP10, followed by juvenile clams; the expression in the mantle gradually decreased with increasing mussel age. A strong signal was detected on epidermal cells on the mantle edge by in situ hybridization. In both the shell notching and inserting operations of the pearl fragment assay, we found that the expression of Hc-BMP10 increased after the above treatments. RNA interference assays showed that the silencing of Hc-BMP10 resulted in a change in the morphology of the prismatic layer and nacreous layer, with the prismatic layer less closely aligned and the disordered aragonite flakes in the nacreous layer. These findings indicate that Hc-BMP10 is involved in the growth and development of H. cumingii, as well as the formation of shells and pearls. Therefore, this study provides some reference for selecting superior species for growth and pearl breeding of H. cumingii at a molecular level and further investigation of the molecular mechanism for biomineralization of Hc-BMP10.

Transcriptome analysis of growth and shell color between two genetic variants of Corbicula fluminea with different shell colors.

To clarify the molecular mechanism of the black and yellow shell coloration, we performed a transcriptome analysis of whole tissue of Corbicula fluminea in Hongze Lake (Jiangsu Province, China). After assembly, 335,247 unigenes were obtained, and 136,804 unigenes were functionally identified using public databases (NR, GO, KEGG, eggnog, and Swissprot). 1567 differentially expressed genes (DEGs) were detected through pairwise comparisons, of which 941 DEGs were up-regulated and 626 were down-regulated in the black-shelled clam. We compared the DEGs between two clams and identified some coloration-related genes. Notably, the black-shelled clam was larger than the yellow-shelled. We speculated that higher digestion and anabolic ability of black-shelled clam might lead to this phenomenon. In contrast, the yellow-shelled clam appeared to be more sensitive to environmental stress. The metabolic energy of the yellow-shelled clam was depleted to maintain or recover from stress, and provide less energy for growth. In summary, our finding provides a theoretical basis for the molecular mechanism of pigmentation and the difference of somatotype in bivalve, as well as promotes the future breeding of more elite varieties.

Identification of complete F-type mitochondrial genome in Lamprotula scripta and Lamprotula caveata and analysis on DUI.

Mitochondrial DNA is typically passed to offspring through maternal inheritance. However, in mussels, two kinds of mitochondrial DNA exist: F and M type, which are referred to as doubly uniparental inheritance (DUI). Studies have shown that DUI may be related to gender determination. In this study, we obtained the first complete F-type mitochondrial genome of Lamprotula scripta and Lamprotula caveata which were 16,250 bp and 16,641 bp in length, respectively, and had 13 protein coding genes (PCGs), 22 transfer RNAs, 2 ribosomal RNAs and 27 non-coding (NC) regions. The largest NC region of L. scripta was 639 bp and located between ND5 and tRNAGln. The largest NC of L. caveata was 1046 bp and also located between ND5 and tRNAGln. The overall AT content of L. scripta and L. caveata was 58.95% and 58.66%, respectively, which were lower than Lamprotula leai, Lamprotula gottschei and Lamprotula tortuosa. We next compared F and M mitochondrial genomic data on freshwater mussels and established a phylogenetic tree based on amino acid sequences of 13 PCGs and COII gene. Our results showed that F- and M-type mitochondria were significantly separated into two branches, and the basic structure of phylogenetic trees were divided into four distinct groups: Unioninae, Anodontini, Gonideinae and Ambleminae. Relatives of Gonideinae and Ambleminae were more closely related than Unioninae and Anodontini, indicating significant differences in mtDNA between the two mitogenome types. Moreover, we revealed that L. scripta and L. caveata are closely relatives, suggesting that they are both subordinates of the Gonideinae subfamily. Consequently, we speculate that the formation of DUI hinders their disappearance, which provides a basis for further studies into the mechanisms and genetic diversities of DUI formation.