Transcriptome analysis of mantle tissues reveals potential biomineralization-related genes in Tectus pyramis Born

The shell formation mechanism of Turbo argyrostomus based on ultrastructure and transcriptome analysis

The gold inner shell of Turbo argyrostomus is an important morphological classification characteristic in Gastropoda. However, the gene sets responsible for shell formation in gastropods remain poorly explored. In this study, we investigated the microstructure using scanning electron microscopy (SEM), hematoxylin-eosin (HE) and Alcian blue staining-periodic acid-Schiff (AB-PAS) staining. The SEM results illustrated that the T. argyrostomus shell exhibited a special "sandwich" microstructure. The results of histological observation demonstrated two major cell types: adipocytes and mucin cells. A total of 318 differentially expressed genes were identified between edge mantle and central mantle, among which whey acidic protein, N66, and nacre-like proteins, and Lam G and EGF domains may be related to shell microstructure. 22.39% - 25.20% of the mucin genes had biomineralization related domains, which supported for the relationship between mucins and shell formation. Moreover, this study revealed energy distribution differences between the edge mantle and central mantle. These results provide insights for further understanding of the biomineralization mechanism in Gastropoda.

Transcriptome analysis of the bivalve Placuna placenta mantle reveals potential biomineralization-related genes

The shells of window pane oyster Placuna placenta are very thin and exhibit excellent optical transparency and mechanical robustness. However, little is known about the biomineralization-related proteins of the shells of P. placenta. In this work, we report the comprehensive transcriptome of the mantle tissue of P. placenta for the first time. The unigenes of the mantle tissue of P. placenta were annotated by using the public databases such as nr, GO, KOG, KEGG, and Pfam. 24,343 unigenes were annotated according to Pfam database, accounting for 21.48% of the total unigenes. We find that half of the annotated unigenes of the mantle tissue of P. placenta are consistent to the annotated unigenes from pacific oyster Crassostrea gigas according to nr database. The unigene sequence analysis from the mantle tissue of P. placenta indicates that 465,392 potential single nucleotide polymorphisms (SNPs) and 62,103 potential indel markers were identified from 60,371 unigenes. 178 unigenes of the mantle tissue of P. placenta are found to be homologous to those reported proteins related to the biomineralization process of molluscan shells, while 18 of them are highly expressed unigenes in the mantle tissue. It is proposed that four unigenes with the highest expression levels in the mantle tissue are very often related to the biomineralization process, while another three unigenes are potentially related to the biomineralization process according to the Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) analysis. In summary, the transcriptome analysis of the mantle tissue of P. Placenta shows the potential biomineralization-related proteins and this work may shed light for the shell formation mechanism of bivalves.

Comparative Transcriptomic and Expression Profiles Between the Foot Muscle and Mantle Tissues in the Giant Triton Snail Charonia tritonis

The giant triton snail (Charonia tritonis), an endangered gastropod species of ecological and economic importance, is widely distributed in coral reef ecosystems of the Indo-West Pacific region and the tropical waters of the South China Sea. Limited research on molecular mechanisms can be conducted because the complete genomic information on this species is unavailable. Hence, we performed transcriptome sequencing of the C. tritonis foot muscle and mantle using the Illumina HiSeq sequencing platform. In 109,722 unigenes, we detected 7,994 (3,196 up-regulated and 4,798 down-regulated) differentially expressed genes (DEGs) from the C. tritonis foot muscle and mantle transcriptomes. These DEGs will provide valuable resources to improve the understanding of molecular mechanisms involved in biomineralization of C. tritonis. In the Gene Ontology (GO) database, DEGs were clustered into three main categories (biological processes, molecular functions, and cellular components) and were involved in 50 functional subcategories. The top 20 GO terms in the molecular function category included sulfotransferase activity, transferring sulfur-containing groups, and calcium ion binding, which are terms considered to be related to biomineralization. In KEGG classifications, transcriptomic DEGs were mainly enriched in glycosaminoglycan biosynthesis-chondroitin sulfate/dermatan sulfate, and sulfur metabolism pathway, which may be related to biomineralization. The results of qPCR showed that three of the eight genes examined were significantly up-regulated in the mantle. The phylogenetic tree of BMP1 suggested a significant divergence between homologous genes in C. tritonis. Our results improve the understanding of biomineralization in C. tritonis and provide fundamental transcriptome information to study other molecular mechanisms such as reproduction.

PfSMAD1/5 Can Interact with PfSMAD4 to Inhibit PfMSX to Regulate Shell Biomineralization in Pinctada fucata martensii

The BMP2 signal transduced by SMAD1/5 plays an important role in osteoblast differentiation and bone formation. Shell formation of Pinctada fucata martensii is a typical biomineralization process that is similar to that of teeth/bone formation. However, whether the Pinctada fucata BMP2 (PfBMP2) signal transduced by PfSMAD1/5 occurs in P. f. martensii, how the PfBMP2 signal is transduced by PfSMAD1/5, and how PfSMAD1/5 regulates the biomineralization process in this species and other shellfish are poorly understood. Therefore, injection experiments of recombinant PfBMP2 and inhibitor dorsomorphin revealed that PfSMAD1/5 can transduce PfBMP2 signals. Subcellular localization and bimolecular fluorescence complementation assays indicated that PfSMAD1/5 phosphorylated by PfBMPR1b interacts with PfSMAD4 in the cytoplasm to form a complex, which translocates to the nucleus to transduce PfBMP2 signals. Co-immunoprecipitation and luciferase assays revealed that PfSMAD1/5 may interact with PfMSX to dislodge it from its binding element, resulting in initiation of mantle gene transcription. The in vivo functional assay showed that knockdown of PfMSAD1/5 decreased expression of shell matrix genes and disordered the nacreous layer, and the correlation assay of shell regeneration showed the concomitant expression pattern of PfSMAD1/5 and shell matrix genes. Together, these data showed that PfSMAD1/5 can transduce PfBMP2 signals to regulate shell biomineralization in P. f. martensii, which illustrated conservation of the BMP2-SMAD signal pathway among invertebrates. Particularly, the results suggest that there is only one PfMSX gene, which functions like the Hox gene in vertebrates, that interacts with PfSMAD1/5 in a protein-protein action form and plays the role of transcription repressor.

Microstructure and in-depth proteomic analysis of Perna viridis shell

For understanding the structural characteristics and the proteome of Perna shell, the microstructure, polymorph, and protein composition of the adult Perna viridis shell were investigated. The P. viridis shell have two distinct mineral layers, myostracum and nacre, with the same calcium carbonate polymorph of aragonite, determined by scanning electron microscope, Fourier transform infrared spectroscopy, and x-ray crystalline diffraction. Using Illumina sequencing, the mantle transcriptome of P. viridis was investigated and a total of 69,859 unigenes was generated. Using a combined proteomic/transcriptomic approach, a total of 378 shell proteins from P. viridis shell were identified, in which, 132 shell proteins identified with more than two matched unique peptides. Of the 132 shell proteins, 69 are exclusive to the nacre, 12 to the myostracum, and 51 are shared by both. The Myosin-tail domain containing proteins, Filament-like proteins, and Chitin-binding domain containing proteins represent the most abundant molecules. In addition, the shell matrix proteins (SMPs) containing biomineralization-related domains, such as Kunitz, A2M, WAP, EF-hand, PDZ, VWA, Collagen domain, and low complexity regions with abundant certain amino acids, were also identified from P. viridis shell. Collagenase and chitinase degradation can significantly change the morphology of the shell, indicating the important roles of collagen and chitin in the shell formation and the muscle-shell attachment. Our results present for the first time the proteome of P. viridis shell and increase the knowledge of SMPs in this genus.