Characterization and expression of tyrosinase-like genes in the anemone Exaiptasia pallida as a function of health and symbiotic state

Structural and Evolutionary Relationships of Melanin Cascade Proteins in Cnidarian Innate Immunity

Melanin is an essential product that plays an important role in innate immunity in a variety of organisms across the animal kingdom. Melanin synthesis is performed by many organisms using the tyrosine metabolism pathway, a general pathway that utilizes a type-three copper oxidase protein, called PO-candidates (phenoloxidase candidates). While melanin synthesis is well-characterized in organisms like arthropods and humans, it is not as well-understood in non-model organisms such as cnidarians. With the rising anthropomorphic climate change influence on marine ecosystems, cnidarians, specifically corals, are under an increased threat of bleaching and disease. Understanding innate immune pathways, such as melanin synthesis, is vital for gaining insights into how corals may be able to fight these threats. In this study, we use comparative bioinformatic approaches to provide a comprehensive analysis of genes involved in tyrosine-mediated melanin synthesis in cnidarians. Eighteen PO-candidates representing five phyla were studied to identify their evolutionary relationship. Cnidarian species were most similar to chordates due to domain presents in the amino acid sequences. From there, functionally conserved domains in coral proteins were identified in a coral disease dataset. Five stony corals exposed to stony coral tissue loss disease were leveraged to identify 18 putative tyrosine metabolism genes, genes with functionally conserved domains to their Homo sapiens counterpart. To put this pathway in the context of coral health, putative genes were correlated to melanin concentration from tissues of stony coral species in the disease exposure dataset. In this study, tyrosinase was identified in stony corals as correlated to melanin concentrations and likely plays a key role in immunity as a resistance trait. In addition, stony coral genes were assigned to all modules within the tyrosine metabolism pathway, indicating an evolutionary conservation of this pathway across phyla. Overall, this study provides a comprehensive analysis of the genes involved in tyrosine-mediated melanin synthesis in cnidarians.

Gene network analyses of larvae under different egg-protecting behaviors provide novel insights into immune response mechanisms of Amphioctopus fangsiao

Amphioctopus fangsiao was a representative economic species in cephalopods, which was vulnerable to marine bacteria. Vibrio anguillarum was a highly infectious pathogen that have recently been found to infect A. fangsiao and inhibit its growth and development. There were significant differences in the immune response mechanisms between egg-protected and egg-unprotected larvae. To explore larval immunity under different egg-protecting behaviors, we infected A. fangsiao larvae with V. anguillarum for 24 h and analyzed the transcriptome data about egg-protected and egg-unprotected larvae infected with 0, 4, 12, and 24 h using weighted gene co-expression networks (WGCNA) and protein-protein interaction (PPI) networks. Network analyses revealed a series of immune response processes after infection, and identified six key modules and multiple immune-related hub genes. Meanwhile, we found that ZNF family, such as ZNF32, ZNF160, ZNF271, ZNF479, and ZNF493 might play significant roles in A. fangsiao immune response processes. We first creatively combined WGCNA and PPI network analysis to deeply explore the immune response mechanisms of A. fangsiao larvae with different egg-protecting behaviors. Our results provided further insights into the immunity of V. anguillarum infected invertebrates, and laid the foundation for exploring the immune differences among cephalopods with different egg protecting behaviors.

Immune properties of invertebrate phenoloxidases

Melanin production from different types of phenoloxidases (POs) confers immunity from a variety of pathogens ranging from viruses and microorganisms to parasites. The arthropod proPO expresses a variety of activities including cytokine, opsonin and microbiocidal activities independent of and even without melanin production. Proteolytic processing of proPO and its activating enzyme gives rise to several peptide fragments with a variety of separate activities in a process reminiscent of vertebrate complement system activation although proPO bears no sequence similarity to vertebrate complement factors. Pathogens influence proPO activation and thereby what types of immune effects that will be produced. An increasing number of specialised pathogens - from parasites to viruses - have been identified who can synthesise compounds specifically aimed at the proPO-system. In invertebrates outside the arthropods phylogenetically unrelated POs are participating in melanization reactions obviously aimed at intruders and/or aberrant tissues.

Differential expression of Exaiptasia pallida GIMAP genes upon induction of apoptosis and autophagy suggests a potential role in cnidarian symbiosis and disease

Coral reefs, one of the world's most productive and diverse ecosystems, are currently threatened by a variety of stressors that result in increased prevalence of both bleaching and disease. Therefore, understanding the molecular mechanisms involved in these responses is critical to mitigate future damage to the reefs. One group of genes that is potentially involved in cnidarian immunity and symbiosis is GTPases of immunity associated proteins (GIMAP). In vertebrates, this family of proteins is involved in regulating the fate of developing lymphocytes and interacts with proteins involved in apoptosis and autophagy. As apoptosis, autophagy and immunity have previously been shown to be involved in cnidarian symbiosis and disease, the goal of this research was to determine the role of cnidarian GIMAPs in these processes using the anemone Exaiptasia pallida To do so, GIMAP genes were characterized in the E. pallida genome and changes in gene expression were measured using qPCR in response to chemical induction of apoptosis, autophagy and treatment with the immune stimulant lipopolysaccharide (LPS) in both aposymbiotic and symbiotic anemones. The results revealed four GIMAP-like genes in E. pallida, referred to as Ep_GIMAPs Induction of apoptosis and autophagy resulted in a general downregulation of Ep_GIMAPs, but no significant changes were observed in response to LPS treatment. This indicates that Ep_GIMAPs may be involved in the regulation of apoptosis and autophagy, and therefore could play a role in cnidarian-dinoflagellate symbiosis. Overall, these results increase our knowledge on the function of GIMAPs in a basal metazoan.