Expression of galaxin and oncogene homologs in growth anomaly in the coral Montipora capitata

The Matrix Protein Cysrichin, a Galaxin-like Protein from Hyriopsis cumingii, Induces Vaterite Formation In Vitro

In this study, we cloned a novel matrix protein, cysrichin, with 16.03% homology and a similar protein structure to the coral biomineralized protein galaxin. Tissue expression analysis showed that cysrichin was mainly expressed in mantle and gill tissues. In situ hybridization indicated that cysrichin mRNA was detected in the entire epithelium region of mantle tissue. RNAi analysis and shell notching experiment confirmed that cysrichin participates in the prismatic layer and nacreous layer formation of the shell. An in vitro crystallization experiment showed that the cysrichin protein induced lotus-shaped and round-shaped crystals, which were identified as vaterite crystals. These results may provide new clues for understanding the formation of vaterite in freshwater shellfish.

Coral growth anomalies, neoplasms, and tumors in the Anthropocene

One of the most widespread coral diseases linked to anthropogenic activities and recorded on reefs worldwide is characterized by anomalous growth formations in stony corals, referred to as coral growth anomalies (GAs). The biological functions of GA tissue include limited reproduction, reduced access to resources, and weakened ability to defend against predators. Transcriptomic analyses have revealed that, in some cases, disease progression can involve host genes related to oncogenesis, suggesting that the GA tissues may be malignant neoplasms such as those developed by vertebrates. The number of studies reporting the presence of GAs in common reef-forming species highlights the urgency of a thorough understanding of the pathology and causative factors of this disease and its parallels to higher organism malignant tissue growth. Here, we review the current state of knowledge on the etiology and holobiont features of GAs in reef-building corals.

A proteomic analysis of skeletal tissue anomaly in the brain coral Platygyra carnosa

Coral skeletal growth anomaly (GA) is a common coral disease. It has been considered as a pathological condition comparable to abnormal tissue growth in mammals, but little is known about the molecular changes underlying coral GA. To investigate the molecular pathology of GA, we compared the proteome between normal and GA-affected tissues of the brain coral Platygyra carnosa using iTRAQ-labeling and LC-MS/MS, which quantified 818 proteins and identified 117 differentially expressed proteins (DEPs). GO analyses revealed DEPs that might be related to GA included "translational elongation", "proteasome core complex", "amine metabolic processes" and "lysosome". Several proteins implicated in calcification and fluorescence were differentially expressed at both protein and mRNA level. Protein-protein interaction network suggested possible involvement of TNF receptor signaling in GA. Overall, our results provided novel insights into the molecular pathology of coral GA, which will pave the way for determination of the causative agent(s) of this coral disease.

Nodular-like growth and axial thickening in gorgonians are a defensive response to endolithic cyanobacteria, involving amyloid deposition

An accurate approach to coral disease study is critical for understanding the global decline of coral populations. Such an approach should involve the proper use of medical concepts and terminology to avoid confusion and promote clarity in the coral disease literature. Inflammatory and neoplastic disorders have been frequently confused in corals. They are both reported as 'growth anomalies' because of their possible gross similarity, but in fact they are very different types of lesions and pathologic phenomena. In this work, we assessed the distribution and prevalence of growth anomalies, externally visible as nodular-like lesions, in the soft corals Eunicella cavolinii and E. singularis in 2008-2009 in 3 different areas along the Campanian coastline of Italy. Histopathology revealed them as chronic inflammatory lesions, resembling chronic inflammatory lesions of vertebrates, encapsulating an unidentified pathogen. Congo red and Masson Fontana histochemistry highlighted an amoebocyte infiltration with the presence of new apposition of melanin coupled with amyloid sheets intended as part of the defensive response, as reported in other invertebrates. A parallel molecular analysis of 16S rRNA of the lesions suggested that the causative agent is an endolithic cyanobacterium belonging to the order Nostocales. This is the first study assessing the presence of amyloid fibrils in corals.

History of perspectives on the study of coral disease in the eastern tropical Pacific

Disease in coral species is one factor associated with the current degradation process of tropical reefs. The history of research on coral pathologies dates to 1970 with the first reports of diseases in the Greater Caribbean and Indo-Pacific regions, although some anecdotal observations were made earlier. Today, there is information on the health conditions of >200 coral species in 70 countries. The special natural conditions under which reefs develop in the eastern tropical Pacific (ETP) and the predominance of a single coral genus, Pocillopora (a host highly susceptible to disease), leave them vulnerable to health impairments and the loss of viability, structure and function in the wider ecosystem. Therefore, coral reefs in the ETP are ideal systems for studies of biodiversity and survivorship. To clarify the status of knowledge on coral diseases in the ETP, we reviewed scientific studies conducted there from 1970-2018, comparing 127 publications to literature on other reef regions in the Pacific. Despite the vulnerability of reefs in the ETP, only limited information exists describing and investigating the etiology of lesions and other signs of health deterioration in corals, and there are few baseline studies of coral reefs or analyses of the spatial and temporal dynamics of disease syndromes. In general, efforts to study coral diseases in the ETP are inadequate.

Molecular pathology of skeletal growth anomalies in the brain coral Platygyra carnosa: A meta-transcriptomic analysis

Coral skeletal growth anomaly (GA) is a common coral disease. Although extensive ecological characterizations of coral GA have been performed, the molecular pathology of this disease remains largely unknown. We compared the meta-transcriptome of normal and GA-affected polyps of Platygyra carnosa using RNA-Seq. Approximately 50 million sequences were generated from four pairs of normal and GA-affected tissue samples. There were 109 differentially expressed genes (DEGs) in P. carnosa and 31 DEGs in the coral symbiont Symbiodinium sp. These differentially expressed host genes were enriched in GO terms related to osteogenesis and oncogenesis. There were several differentially expressed immune genes, indicating the presence of both bacteria and viruses in GA-affected tissues. The differentially expressed Symbiodinium genes were enriched in reproduction, nitrogen metabolism and pigment formation, indicating that GA affects the physiology of the symbiont. Our results have provided new insights into the molecular pathology of coral GA.

De novo metatranscriptome assembly and coral gene expression profile of Montipora capitata with growth anomaly

Background

Scleractinian corals are a vital component of coral reef ecosystems, and of significant cultural and economic value worldwide. As anthropogenic and natural stressors are contributing to a global decline of coral reefs, understanding coral health is critical to help preserve these ecosystems. Growth anomaly (GA) is a coral disease that has significant negative impacts on coral biology, yet our understanding of its etiology and pathology is lacking. In this study we used RNA-seq along with de novo metatranscriptome assembly and homology assignment to identify coral genes that are expressed in three distinct coral tissue types: tissue from healthy corals (“healthy”), GA lesion tissue from diseased corals (“GA-affected”) and apparently healthy tissue from diseased corals (“GA-unaffected”). We conducted pairwise comparisons of gene expression among these three tissue types to identify genes and pathways that help us to unravel the molecular pathology of this coral disease.

Results

The quality-filtered de novo-assembled metatranscriptome contained 76,063 genes, of which 13,643 were identified as putative coral genes. Overall gene expression profiles of coral genes revealed high similarity between healthy tissue samples, in contrast to high variance among diseased samples. This indicates GA has a variety of genetic effects at the colony level, including on seemingly healthy (GA-unaffected) tissue. A total of 105 unique coral genes were found differentially expressed among tissue types. Pairwise comparisons revealed the greatest number of differentially expressed genes between healthy and GA-affected tissue (93 genes), followed by healthy and GA-unaffected tissue (33 genes), and GA-affected and -unaffected tissue (7 genes). The putative function of these genes suggests GA is associated with changes in the activity of genes involved in developmental processes and activation of the immune system.

Conclusion

This is one of the first transcriptome-level studies to investigate coral GA, and the first metatranscriptome assembly for the M. capitata holobiont. The gene expression data, metatranscriptome assembly and methodology developed through this study represent a significant addition to the molecular information available to further our understanding of this coral disease.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4090-y) contains supplementary material, which is available to authorized users.