A proteomic approach reveals biomineralization and immune response for mantle to pearl sac in the freshwater pearl mussel (Hyriopsis cumingii)

The molecular response of Mytilus coruscus mantle to shell damage under acute acidified sea water revealed by iTRAQ based quantitative proteomic analysis

Mytilus coruscus is an economically important marine bivalve that lives in estuarine sea areas with seasonal coastal acidification and frequently suffers shell injury in the natural environment. However, the molecular responses and biochemical properties of Mytilus under these conditions are not fully understood. In the present study, we employed tandem mass spectrometry combined with isobaric tagging to identify differentially expressed proteins in the mantle tissue of M. coruscus under different short-term treatments, including shell-complete mussels raised in normal seawater (pH 8.1), shell-damaged mussels raised in normal seawater (pH 8.1), and acidified seawater (pH 7.4). A total of 2694 proteins were identified in the mantle, and analysis of their relative abundance from the three different treatments revealed alterations in the proteins involved in immune regulation, oxidation-reduction processes, protein folding and processing, energy provision, and cytoskeleton. The results obtained by quantitative proteomic analysis of the mantle allowed us to delineate the molecular strategies adopted by M. coruscus in the shell repair process in acidified environments, including an increase in proteins involved in oxidation-reduction processes, protein processing, and cell growth at the expense of proteins involved in immune capacity and energy metabolism. SIGNIFICANCE: The impact of global ocean acidification on calcifying organisms has become a major ecological and environmental problem in the world. Mytilus coruscus is an economically important marine bivalve living in estuary sea area with seasonal coastal acidification, and frequently suffering shell injury in natural environment. Molecular responses of M coruscus under the shell damage and acute acidification is still largely unknown. For this reason, iTRAQ based quantitative proteomic and histological analysis of the mantle from M. coruscus under shell damage and acute acidification were performed, for revealing the proteomic response and possible adaptation mechanism of Mytilus under combined shell damage and acidified sea water, and understanding how the mussel mantle implement a shell-repair process under acidified sea water. Our study provides important data for understanding the shell repair process and proteomic response of Mytilus under ocean acidification, and providing insights into potential adaptation of mussels to future global change.

Transcriptomic and proteomic strategies to reveal the mechanism of Gymnocypris przewalskii scale development

BACKGROUND

Fish scales are typical products of biomineralization and play an important role in the adaptation of fish to their environment. The Gymnocypris przewalskii scales are highly specialized, with scales embedded in only specific parts of the dermis, such as the areas around the anal fin and branchiostegite, making G. przewalskii an ideal material for biomineralization research. In this study, we aimed to unveil genes and pathways controlling scale formation through an integrated analysis of both transcriptome and proteome, of which G. przewalskii tissues of the dorsal skin (no scales) and the rump side skin (with scales) were sequenced. The sequencing results were further combined with cellular experiments to clarify the relationship between genes and signaling pathways.

RESULTS

The results indicated the following: (1) a total of 4,904 differentially expressed genes were screened out, including 3,294 upregulated genes and 1,610 downregulated genes (with a filtering threshold of |log2Fold-Change|> 1 and p-adjust < 0.05). The identified differentially expressed genes contained family members such as FGF, EDAR, Wnt10, and bmp. (2) A total of 535 differentially expressed proteins (DEPs) were filtered out from the proteome, with 204 DEPs downregulated and 331 DEPs upregulated (with a filtering threshold of |Fold-Change|> 1.5 and p < 0.05). (3) Integrated analyses of transcriptome and proteome revealed that emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were important genes contributing to scale development and that PI3K-AKT was the most important signaling pathway involved. (4) With the use of the constructed G. przewalskii fibroblast cell line, emefp1, col1a1, col6a2, col16a1, krt8, and krt18 were confirmed to be positively regulated by the PI3K-AKT signaling pathway.

CONCLUSION

This study provides experimental evidence for PI3K-AKT controlled scale development in G. przewalskii and would benefit further study on stress adaptation, scale biomineralization, and the development of skin appendages.

Transcriptomic response of Mytilus coruscus mantle to acute sea water acidification and shell damage

Mytilus coruscus is an economically important marine calcifier living in the Yangtze River estuary sea area, where seasonal fluctuations in natural pH occur owing to freshwater input, resulting in a rapid reduction in seawater pH. In addition, Mytilus constantly suffers from shell fracture or injury in the natural environment, and the shell repair mechanisms in mussels have evolved to counteract shell injury. Therefore, we utilized shell-complete and shell-damaged Mytilus coruscus in this study and performed transcriptomic analysis of the mantle to investigate whether the expression of mantle-specific genes can be induced by acute seawater acidification and how the mantle responds to acute acidification during the shell repair process. We found that acute acidification induced more differentially expressed genes than shell damage in the mantle, and the biomineralization-related Gene Ontology terms and KEGG pathways were significantly enriched by these DEGs. Most DEGs were upregulated in enriched pathways, indicating the activation of biomineralization-related processes in the mussel mantle under acute acidification. The expression levels of some shell matrix proteins and antimicrobial peptides increased under acute acidification and/or shell damage, suggesting the molecular modulation of the mantle for the preparation and activation of the shell repairing and anti-infection under adverse environmental conditions. In addition, morphological and microstructural analyses were performed for the mantle edge and shell cross-section, and changes in the mantle secretory capacity and shell inner film system induced by the two stressors were observed. Our findings highlight the adaptation of M. coruscus in estuarine areas with dramatic fluctuations in pH and may prove instrumental in its ability to survive ocean acidification.

CgWnt-1 regulates haemocyte proliferation during immune response of oyster Crassostrea gigas

Recent findings regarding the immunomodulatory role of Wnt signaling suggest that it is significant in regulating the differentiation and proliferation of immune cells. In the present study, a Wnt-1 homolog (designated as CgWnt-1) with a conserved WNT1 domain was identified from oyster Crassostrea gigas. The transcripts of CgWnt-1 were barely expressed in egg to gastrula stage during early embryogenesis, and up-regulated significantly in the trochophore to juvenile stage. The mRNA transcripts of CgWnt-1 were detected in different tissues of adult oyster, with an extremely high expression level in the mantle, which was 77.38-fold (p < 0.05) of that in labial palp. After Vibrio splendidus stimulation, the mRNA expression levels of CgWnt-1 and Cgβ-catenin in haemocytes up-regulated significantly at 3, 12, 24, and 48 h (p < 0.05). After injection of recombinant protein (rCgWnt-1) into oyster in vivo, the expressions of Cgβ-catenin, cell proliferation related genes CgRunx-1 and CgCDK-2 in haemocytes significantly up-regulated, which were 4.86-fold (p < 0.05), 9.33-fold (p < 0.05), 6.09-fold (p < 0.05) of those in rTrx group, respectively. The percentage of EDU⁺ cells in haemocytes also significantly increased (2.88-fold of that in control group, p < 0.05) at 12 h after rCgWnt-1 treatment. When the Wnt signal inhibitor C59 was injected simultaneously with rCgWnt-1, the expressions of Cgβ-catenin, CgRunx-1, and CgCDK-2 were significantly reduced, which were 0.32-fold (p < 0.05), 0.16-fold (p < 0.05), and 0.25-fold (p < 0.05) of that in rCgWnt-1 group, respectively, and the percentage of EDU⁺ cells in haemocytes was also significantly inhibited (0.15-fold compared with that in rCgWnt-1 group, p < 0.05). These results suggested that the conserved CgWnt-1 could modulate haemocytes proliferation via regulating cell cycle related genes and involved in the immune response of oysters.

Presence of immune factors in freshwater mussel (Hyriopsis cumingii) entails autologous serum an essential component in the culture of mantle cells

Mussel cell culture is a challenging problem and serum serves a crucial biological role in cell culture as an autologous supply and an immunizing agent. In this study, the biology (calcium ions, total protein, pH, and osmotic pressure) of fetal bovine serum (FBS) and Hyriopsis cumingii serum (HCS) was investigated, and the development of Hyriopsis cumingii (H. cumingii) mantle cells in HCS and FBS systems was examined. The results showed that total protein, calcium ions, and osmotic pressure varied significantly (p<0.05). The activity of mantle cells was superior in the HCS culture system to that in the FBS culture system. The label-free technique was used to distinguish the two serum proteins to investigate the supportive effect of autologous serum on cell culture. These were examined for 109 unique proteins and 35 particular HCS proteins. Most differentially expressed proteins (DEPs) were involved in immune response, cell differentiation, and calcium ion binding. Furthermore, immune factors such as HSP, CALR, APOB, C3 were identified with significant differences. HSP was significantly more present in HCS than in FBS as an endogenous protective protein that regulates immune system function, cell differentiation, transport, and activity regulation. Parallel reaction monitoring (PRM) analysis was carried out to validate the expression levels of 19 DEPs, indicating high reliability of the proteomic results. This study reveals the important role of immune factors in mussel cell culture, providing a theoretical basis for explaining the applicability of autologous serum in cell culture. It is also helpful in improving the cell culture conditions of mussels.