The complexity of porphyrin-like pigments in a marine annelid sheds new light on haem metabolism in aquatic invertebrates

Secretory Cells in Halla parthenopeia (Oenonidae): Potential Implications for the Feeding and Defence Strategies of a Carnivorous Burrowing Polychaete

Carnivorous polychaetes are known to bear diversified and often unique anatomical and behavioural adaptations for predation and defence. Halla parthenopeia, a species known to be a specialized predator of clams, thrives in the soft bottoms of the Mediterranean Sea, holding potential for polyculture and biotechnology due to the secretion of bioactive compounds. Our objective was to provide a comprehensive description of H. parthenopeia's anatomy and microanatomy, shedding light on the relation between morphology and habitat, chemical defences, and feeding behaviour. The pharynx, housing maxillae and mandibles connected to an extensive mucus gland, occupies a considerable portion of the worm's length, reaching beyond the oesophagus. This unique gland is responsible for secreting the feeding mucus, which immobilizes and aids in the digestion of clams probably acting as a vehicle of bioactive compounds synthesized by specialized serous cells in the mouth. Moreover, H. parthenopeia combines behavioural tactics, such as burrowing, and anatomical defences to evade predators. Examination of its epidermis revealed a thick cuticle layer and abundant mucocytes secreting locomotion mucus, both of which save the worm from mechanical harm during movement. When it is preyed upon, the worm can release a substantial amount of Hallachrome, a toxic anthraquinone produced by specific cells in its distal region. This pigment, with its known antimicrobial properties, likely acts as a chemical shield in case of injury. The results suggest that the ability of H. parthenopeia to prey on bivalves and to provide mechanical protection plus defence against pathogens rely on its ability to secrete distinct types of mucus. The interplay between highly specialized microanatomical features and complex behaviours underscores its adaptation as a predator in marine benthic environments.

Protoporphyrin IX metabolism mediated via translocator protein (CgTspO) involved in orange shell coloration of pacific oyster (Crassostrea gigas)

Mollusc shell color polymorphism is influenced by various factors. Pigments secreted in vivo by animals play a critical role in shell coloration. Among the different shell-color hues, orange pigmentation has been partially attributed to porphyrins. However, the detailed causal relationship between porphyrins and orange-shell phenotype in molluscs remains largely unexplored. The various strains of Pacific oyster (Crassostrea gigas) with different shell color provide useful models to study the molecular regulation of mollusc coloration. Accordingly, oysters with orange and gold-shells, exhibiting distinct porphyrin distributions, were selected for analysis of total metabolites and gene expression profile through mantle metabolomic and transcriptomic studies. Translocator protein (TspO) and protoporphyrin IX (PPIX) were identified as potential factors influencing oyster shell-color. The concentration of PPIX was measured using HPLC, while expression profiling of CgTspO was analyzed by qPCR, in situ hybridization, Western blotting, and immunofluorescence techniques. Moreover, the roles of CgTspO in regulating PPIX metabolism and affecting the orange-shell-coloration were investigated in vitro and in vivo. These studies indicate that PPIX and its associated metabolic protein, CgTspO may serve as new regulators of orange-shell-coloration in C. gigas. Data of this study offer new insights into oyster shell coloration and enhancing understandings of mollusc shell color polymorphism.

Endogenous Fluorescent Proteins in the Mucus of an Intertidal Polychaeta: Clues for Biotechnology

The vast ocean holds many unexplored organisms with unique adaptive features that enable them to thrive in their environment. The secretion of fluorescent proteins is one of them, with reports on the presence of such compounds in marine annelids being scarce. The intertidal Eulalia sp. is an example. The worm secretes copious amounts of mucus, that when purified and concentrated extracts, yield strong fluorescence under UV light. Emission has two main maxima, at 400 nm and at 500 nm, with the latter responsible for the blue–greenish fluorescence. Combining proteomics and transcriptomics techniques, we identified ubiquitin, peroxiredoxin, and 14-3-3 protein as key elements in the mucus. Fluorescence was found to be mainly modulated by redox status and pH, being consistently upheld in extracts prepared in Tris-HCl buffer with reducing agent at pH 7 and excited at 330 nm. One of the proteins associated with the fluorescent signal was localized in secretory cells in the pharynx. The results indicate that the secretion of fluorescent proteinaceous complexes can be an important defense against UV for this dweller. Additionally, the internalization of fluorescent complexes by ovarian cancer cells and modulation of fluorescence of redox status bears important considerations for biotechnological application of mucus components as markers.

Transcriptional identification of genes light-interacting in the extraretinal photoreceptors of the crayfish Procambarusclarkii

Crayfish serve as a model for studying the effect of environmental lighting on locomotor activity and neuroendocrine functions. The effects of light on this organism are mediated differentially by retinal and extraretinal photoreceptors located in the cerebroid ganglion and the pleonal nerve cord. However, some molecular aspects of the phototransduction cascade in the pleonal extraretinal photoreceptors remain unknown. In this study, transcriptome data from the pleonal nerve cord of the crayfish Procambarusclarkii (Girard,1852) were analyzed to identify transcripts that potentially interact with phototransduction process. The Illumina MiSeq System and the pipeline Phylogenetically Informed Annotation (PIA) were employed, which places uncharacterized genes into pre-calculated phylogenies of gene families. Here, for the first time 62 transcripts identified from the pleonal nerve cord that are related to light-interacting pathways are reported; they can be classified into the following 11 sets: 1) retinoid pathway in vertebrates and invertebrates, 2) photoreceptor specification, 3) rhabdomeric phototransduction, 4) opsins 5) ciliary phototransduction, 6) melanin synthesis, 7) pterin synthesis, 8) ommochrome synthesis, 9) heme synthesis, 10) diurnal clock, and 11) crystallins. Moreover, this analysis comparing the sequences located on the pleonal nerve cord to eyestalk sequences reported in other studies reveals 94-100% similarity between the 55 common proteins identified. These results show that both retinal and pleonal non-visual photoreceptors in the crayfish equally expressed the transcripts involved in light detection. Moreover, they suggest that the genes related to ocular and extraocular light perception in the crayfish P.clarkii use biosynthesis pathways and phototransduction cascades commons.

Abyssal Benthic Rover, an autonomous vehicle for long-term monitoring of deep-ocean processes

[Figure: see text].

A Transcriptomic Approach to the Metabolism of Tetrapyrrolic Photosensitizers in a Marine Annelid

The past decade has seen growing interest in marine natural pigments for biotechnological applications. One of the most abundant classes of biological pigments is the tetrapyrroles, which are prized targets due their photodynamic properties; porphyrins are the best known examples of this group. Many animal porphyrinoids and other tetrapyrroles are produced through heme metabolic pathways, the best known of which are the bile pigments biliverdin and bilirubin. Eulalia is a marine Polychaeta characterized by its bright green coloration resulting from a remarkably wide range of greenish and yellowish tetrapyrroles, some of which have promising photodynamic properties. The present study combined metabolomics based on HPLC-DAD with RNA-seq transcriptomics to investigate the molecular pathways of porphyrinoid metabolism by comparing the worm’s proboscis and epidermis, which display distinct pigmentation patterns. The results showed that pigments are endogenous and seemingly heme-derived. The worm possesses homologs in both organs for genes encoding enzymes involved in heme metabolism such as ALAD, FECH, UROS, and PPOX. However, the findings also indicate that variants of the canonical enzymes of the heme biosynthesis pathway can be species- and organ-specific. These differences between molecular networks contribute to explain not only the differential pigmentation patterns between organs, but also the worm’s variety of novel endogenous tetrapyrrolic compounds.

Chemical evidence of rare porphyrins in purple shells of Crassostrea gigas oyster

The colour of oyster shells is a very diverse characteristic morphotype, forming intriguing vivid patterns both on the inside and outside of the shell. In the present study, we have identified for the first time, the presence of several porphyrins as constituents of the shell pigmentation of the Crassostrea gigas oyster consumed worldwide. The precise molecular structures of halochromic, fluorescent and acid-soluble porphyrins, such as uroporphyrin and turacin, are unambiguously determined by reverse phase liquid chromatography combined with high resolution mass spectrometry. Their presence account for the purple colouration of shells but also for the dark colouration of adductor muscle scars. We have also defined the endogenous origin of these porphyrins, specifically secreted or accumulated by the shell forming tissue. These findings are pioneering analytical proofs of the existence of the haem pathway in the edible oyster Crassostrea gigas, evidenced by the chemical identification of haem side-products and supported by the recent publication of the corresponding oyster genome.

Light-Mediated Toxicity of Porphyrin-Like Pigments from a Marine Polychaeta

Porphyrins and derivatives form one of the most abundant classes of biochromes. They result from the breakdown of heme and have crucial physiological functions. Bilins are well-known representatives of this group that, besides significant antioxidant and anti-mutagenic properties, are also photosensitizers for photodynamic therapies. Recently, we demonstrated that the Polychaeta Eulalia viridis, common in the Portuguese rocky intertidal, holds a high variety of novel greenish and yellowish porphyrinoid pigments, stored as granules in the chromocytes of several organs. On the follow-up of this study, we chemically characterized pigment extracts from the worm’s skin and proboscis using HPLC and evaluated their light and dark toxicity in vivo and ex vivo using Daphnia and mussel gill tissue as models, respectively. The findings showed that the skin and proboscis have distinct patterns of hydrophilic or even amphiphilic porphyrinoids, with some substances in common. The combination of the two bioassays demonstrated that the extracts from the skin exert higher dark toxicity, whereas those from the proboscis rapidly exert light toxicity, then becoming exhausted. One particular yellow pigment that is highly abundant in the proboscis shows highly promising properties as a natural photosensitizer, revealing that porphyrinoids from marine invertebrates are important sources of these high-prized bioproducts.