Chemical defense in ascidians of the didemnidae family

Site-directed late-stage diversification of macrocyclic nannocystins facilitating anticancer SAR and mode of action studies

Nannocystins are a family of 21-membered cyclodepsipeptides with excellent anticancer activity. However, their macrocyclic architecture poses a significant challenge to structure modification. Herein, this issue is addressed by leveraging the strategy of post-macrocyclization diversification. In particular, a novel serine-incorporating nannocystin was designed so that its appending hydroxyl group could diversify into a wide variety of side chain analogues. Such effort facilitated not only structure-activity correlation at the subdomain of interest, but also the development of a macrocyclic coumarin-labeled fluorescence probe. Uptake experiments indicated good cell permeability of the probe, and endoplasmic reticulum was identified as its subcellular localization site.

Existence in cellulose shelters: industrial and pharmaceutical leads of symbiotic actinobacteria from ascidian Phallusia nigra, Andaman Islands

The diversity of actinobacteria associated with marine ascidian Phallusia nigra from Andaman Islands was investigated. A total of 10 actinobacteria were isolated and based on the biochemical and molecular characterization, the isolates were assigned to 7 different actinobacterial genera. Eight putatively novel species belonging to genera Rhodococcus, Kineococcus, Kocuria, Janibacter, Salinispora and Arthrobacter were identified based on 16S rDNA sequence similarity with the NCBI database. The organic extracts of ten isolates displayed considerable bioactivity against test pathogens, which were Gram-positive and Gram-negative in nature. PCR-based screening for type I and type II polyketide synthases (PKS-I, PKS-II) and nonribosomal peptide synthetases (NRPS) revealed that, 10 actinobacterial isolates encoded at least one type of polyketide synthases biosynthesis gene. Majority of the isolates found to produce industrially important enzymes; amylase, protease, gelatinase, lipase, DNase, cellulase, urease, phosphatase and L-asparaginase. The present study emphasized that, ascidians are a prolific resource for novel bioactive actinobacteria with potential for novel drug discovery. This result expands the scope to functionally characterize the novel ascidian associated marine actinobacteria and their metabolites could be a source for the novel molecules of commercial interest.

Bioactive Metabolites from Marine Ascidians: Future Treatment for Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a developmental disorder that influences communication and behavior. Numerous researches propose that genes can act together with manipulations from the environment to affect development in ways that lead to ASD. The broad range of issues facing people with ASD means that there is no single proper drug and treatment for ASD. Numerous shortcomings associated with the present conventional therapeutic strategies have forced researchers to venture into alternative natural sources for effective compounds. The marine environment has emerged as an alternate search environment due to its versatile conditions where organisms employ various biodefense mechanisms for their survival. Ascidians are an excellent source for unique bioactive compounds with nutritive and therapeutic content and it still holds credit for being an underused source from marine animals. Bioactive compounds isolated from ascidians have various commendable biomedical applications due to their unique chemical structures. The present chapter will focus on the potential of bioactive compounds derived from ascidians for the treatment of the neurologic disorder-ASD.

Proceraea exoryxae sp. nov. (Annelida, Syllidae, Autolytinae), the first known polychaete miner tunneling into the tunic of an ascidian

While studying organisms living in association with the solitary tunicate Phallusia nigra (Ascidiacea, Ascidiidae) from a shallow fringing reef at Zeytouna Beach (Egyptian Red Sea), one of the collected ascidians showed peculiar perforations on its tunic. Once dissected, the perforations revealed to be the openings of a network of galleries excavated in the inner tunic (atrium) by at least six individuals of a polychaetous annelid. The worms belonged to the Autolytinae (Syllidae), a subfamily that is well known to include specialized predators and/or symbionts, mostly associated with cnidarians. The Red Sea worms are here described as Proceraea exoryxae sp. nov., which are anatomically distinguished by the combination of simple chaetae only in anterior chaetigers, and a unique trepan with 33 teeth in one outer ring where one large tooth alternates with one medium-sized tricuspid tooth, and one inner ring with small teeth located just behind the large teeth. Male and female epitokes were found together with atokous individuals within galleries. Proceraea exoryxae sp. nov. constitutes the first known miner in the Autolytinae and the second species in this taxon known to live symbiotically with ascidians. The implications of finding this specialized parasite are discussed considering that Phallusia nigra has been introduced worldwide, in tropical and sub-tropical ecosystems, where it has the potential of becoming invasive.

Distinct community dynamics at two artificial habitats in a recreational marina

Man-made facilities along coastlines modify water circulation and sedimentation dynamics which can affect the structure of marine benthic and pelagic communities. To test how environmental heterogeneity associated with a recreational marina affects the structure of the fouling community and the benthic-pelagic link, we conducted an experiment in which predation effects on recruitment and community structure were assessed in two artificial habitats: inside the marina, an area of calm waters and often disturbed by boating activity, and the breakwater, a more hydrodynamic area. Using visual censuses and video footages we also described the predation pressure and the identity of predators on the two areas. Inside the marina, the recruitment of ascidians and serpulids, but not of bryozoans, was restricted in some occasions, possibly due to reduced water circulation. Predation, mainly by the silver porgy fish Diplodus argenteus, reduced the survivor of didemnid ascidians on both areas, but predation intensity was 40 times higher in the breakwater than inside the marina. While the two artificial habitats did not necessarily support distinct communities, low recruitment coupled to weak predation inside the marina, a less dynamic environment, likely imply lower resilience and more susceptibility to disturbance.

The secret to a successful relationship: lasting chemistry between ascidians and their symbiotic bacteria

Bioactive secondary metabolites are common components of marine animals. In many cases, symbiotic bacteria, and not the animals themselves, synthesize the compounds. Among marine animals, ascidians are good models for understanding these symbioses. Ascidians often contain potently bioactive secondary metabolites as their major extractable components. Strong evidence shows that ~8% of the known secondary metabolites from ascidians are made by symbiotic bacteria, and indirect evidence implicates bacteria in the synthesis of many more. Far from being "secondary" to the animals, secondary metabolites are essential components of the interaction between host animals and their symbiotic bacteria. These interactions have complex underlying biology, but the chemistry is clearly ascidian-species specific. The chemical interactions are ancient in at least some cases, and they are widespread among ascidians. Ascidians maintain secondary metabolic symbioses with bacteria that are phylogenetically diverse, indicating a convergent solution to obtaining secondary metabolites and reinforcing the importance of secondary metabolism in animal survival.

Species specificity of symbiosis and secondary metabolism in ascidians

Ascidians contain abundant, diverse secondary metabolites, which are thought to serve a defensive role and which have been applied to drug discovery. It is known that bacteria in symbiosis with ascidians produce several of these metabolites, but very little is known about factors governing these 'chemical symbioses'. To examine this phenomenon across a wide geographical and species scale, we performed bacterial and chemical analyses of 32 different ascidians, mostly from the didemnid family from Florida, Southern California and a broad expanse of the tropical Pacific Ocean. Bacterial diversity analysis showed that ascidian microbiomes are highly diverse, and this diversity does not correlate with geographical location or latitude. Within a subset of species, ascidian microbiomes are also stable over time (R=-0.037, P-value=0.499). Ascidian microbiomes and metabolomes contain species-specific and location-specific components. Location-specific bacteria are found in low abundance in the ascidians and mostly represent strains that are widespread. Location-specific metabolites consist largely of lipids, which may reflect differences in water temperature. By contrast, species-specific bacteria are mostly abundant sequenced components of the microbiomes and include secondary metabolite producers as major components. Species-specific chemicals are dominated by secondary metabolites. Together with previous analyses that focused on single ascidian species or symbiont type, these results reveal fundamental properties of secondary metabolic symbiosis. Different ascidian species have established associations with many different bacterial symbionts, including those known to produce toxic chemicals. This implies a strong selection for this property and the independent origin of secondary metabolite-based associations in different ascidian species. The analysis here streamlines the connection of secondary metabolite to producing bacterium, enabling further biological and biotechnological studies.

Visualization of plant cell wall lignification using fluorescence-tagged monolignols

Lignin is an abundant phenylpropanoid polymer produced by the oxidative polymerization of p-hydroxycinnamyl alcohols (monolignols). Lignification, i.e., deposition of lignin, is a defining feature of secondary cell wall formation in vascular plants, and provides an important mechanism for their disease resistance; however, many aspects of the cell wall lignification process remain unclear partly because of a lack of suitable imaging methods to monitor the process in vivo. In this study, a set of monolignol analogs γ-linked to fluorogenic aminocoumarin and nitrobenzofuran dyes were synthesized and tested as imaging probes to visualize the cell wall lignification process in Arabidopsis thaliana and Pinus radiata under various feeding regimens. In particular, we demonstrate that the fluorescence-tagged monolignol analogs can penetrate into live plant tissues and cells, and appear to be metabolically incorporated into lignifying cell walls in a highly specific manner. The localization of the fluorogenic lignins synthesized during the feeding period can be readily visualized by fluorescence microscopy and is distinguishable from the other wall components such as polysaccharides as well as the pre-existing lignin that was deposited earlier in development.

Didemnins, tamandarins and related natural products

Since the discovery and isolation of the didemnin family of marine depsipeptides in 1981, the synthesis and biological activity of its congeners have been of great interest to the scientific community. The didemnins have demonstrated antitumor, antiviral, and immunosuppressive activity at low nano- and femtomolar levels. Of the congeners, didemnin B was the first marine natural product to reach phase II clinical trials in the United States, stimulating many analogue syntheses to date. About two decades later, tamandarins A and B were isolated, and were found to possess very similar structure and biological activity to that of the didemnin B. These compounds have shown impressive biological activity and some progress has been made in establishing structure-activity relationships. However, their molecular mechanism of action still remains unclear. This review highlights the long-standing study of didemnins and its critical application towards the understanding of the molecular mechanism of action of tamandarins and their potential use as therapeutic agents.

Synthetic studies of tamandarin B side chain analogues

The syntheses of three tamandarin B analogues are described. The goal of these studies was to prepare material to determine their relative therapeutic index and to gain an oversight as to their potential for clinical applications.

Total Synthesis and Biological Evaluation of Tamandarin B Analogues

Tamandarins A and B are a class of marine natural cyclodepsipeptides with structures and biological activities closely related to those of the didemnins. The easier synthetic access to tamandarins accelerates the preparation of new macrocyclic derivatives of this family of antitumor, antiviral, and immunosuppressive compounds. The optimization of the previously reported synthetic route to tamandarins by changing the macrolactamization site from Nst1 and Thr6 to Pro4 and N,O-Me2Tyr5 residues led to a significant improvement in the reaction yield. Using this new synthetic approach, four new macrocyclic analogues of tamandarin B were prepared and evaluated for anticancer activity. These results provide further insight into the structure-activity relationship of the tamandarins and didemnins.

Synthesis and biological evaluation of tamandarin B analogues

[structure: see text]. The synthesis of two tamandarin B analogues in which the N,O-Me2Tyr5 unit was replaced by N-Me-phenylalanine (N-MePhe5) and (S)-2-(methylamino)-3-(naphthalen-2-yl)propanoic acid (N-MeNaphth5) is described. The choice of the macrocyclization site was crucial to achieve satisfactory macrolactamization. Coupling between norstatine (Nst1) and threonine (Thr6) afforded only a 15% yield, while lactamization between proline (Pro4) and the aromatic moiety could be achieved in 65% yield.

Serotonin--a link between disgust and immunity?

Immune systems maintain the integrity of organisms by recognising and attacking foreign substances and/or pathogens. However, immune defences can only take place following direct contact with threats. Disgust can prevent infection before contact with potential pathogens: we propose that disgust is an evolved nervous response to a signal reliably co-occurring with infectious environmental disease threats, which motivates behaviour leading to the avoidance of infection. We hypothesize that disgust and immunity form a defensive continuum with overlaps: disgust acts prior to contact with the infectious agent and prevents it from getting into the body; emesis (vomiting) gets it out once inside the gastrointestinal tract, before penetration of the body boundaries; and immunity expels or kills infectious threats following penetration of the body proper. We further propose that serotonin (5-hydroxytryptamine, 5-HT) might be the link between disgust and immunity. 5-HT plays a central role in the induction of the emetic reflex and is possibly involved in the development of learned aversion; it is also a signal used by immune cells and modulates both innate and acquired immunity. We therefore propose 5-HT might mediate the interaction between these two defensive mechanisms.

In vivo reporter labeling of proteins via metabolic delivery of coenzyme A analogues

We demonstrate site-specific reporter labeling of proteins within live cells. By accessing the coenzyme A (CoA) metabolic pathway with a cell-permeable pantetheine analogue, we deliver CoA-bound reporter molecules for post-translational protein modification in vivo. These methods may be applied to natural product pathway manipulation as well as applications in conventional molecular and cellular biology.

Fluorescent Profiling of Natural Product Producers

The identification of natural product producer organisms remains a problem for both isolation and natural product classification. A concise screen is developed through fluorescent modification of a set of natural products that offer a common activity. Through real-time multicolor microscopy, the processing, storage, and effects of a natural product are rapidly screened at the level of the strain and individual organism.

Marine natural products

This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country or origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any first total syntheses of a marine natural product.

Ecology and natural history of the protochordates

The last comprehensive reviews of ecology and natural history of ascidians were included in the excellent 1971 publication by Millar on the biology of ascidians and the 1991 treatise on New Caledonia ascidians by Monniot, Monniot, and Laboute. Several hundred papers have been published since that time, greatly expanding our knowledge of environmental tolerances and responses to increasing levels of anthropogenically derived toxins in marine waters, energetics and feeding strategies, predator–prey relationships, competition both intra- and inter-specific that include many studies of self–nonself recognition in colonial species, modes and environmental regulation of reproduction and development, symbionts, natural-product chemistry as antifouling and antipredator defenses, and dispersal mechanisms. The relatively new field of molecular genetics is revealing the presence of cryptic species and is helping to determine the origin of anthropogenically transported individuals, an important and growing problem that affects natural ecological relationships in marine communities worldwide. We are learning more about the difficult-to-study abyssal and Antarctic species. There have been great advances in our understanding of the importance in open-ocean food webs of the planktonic Appendicularia and Thaliacea. Also included in this review is a brief discussion of recent work on the Cephalochordata and Hemichordata.

Establishment and characterisation of a human carcinoma cell line with acquired resistance to Aplidin

Aplidin (APL) is a new antitumoral drug from marine origin currently in phase II clinical trials against a wide multiplicity of cancers. As resistance may be, as with other drugs, an important obstacle to the APL therapeutic efficacy, we have established an acquired resistance cellular model by continuous exposure of HeLa cells to the drug. The stably resistant subline generated (HeLa-APL), possessing more than 1000-fold relative resistance to APL than parental cells, did not show crossresistance to a subset of clinically relevant antitumoral agents. In addition, resistance was not related to overexpression of P-glycoprotein or differences in overall drug accumulation. Comparing to parental cells, HeLa-APL cells did not present either significant differences in the growth rate or apparent alterations in the cell cycle distribution. Aplidin induced rapid and persistent phosphorylation of both JNK and p38 MAPKs, resulting in activation of the mitochondrial apoptotic pathway in parental cells, but, notably, in HeLa-APL-resistant cells MAPKs activation only occurred in a slight and transiently manner, failing to activate the above-mentioned apoptotic machinery. These results suggest that sustained activation of JNK and p38 is essential for triggering the apoptotic programme induced by APL and that HeLa-APL cells bypass this apoptotic response by preventing the specific mechanisms that prime and sustain the long-term activation of these signalling cascades. Although far from human tumour physiology in vivo, HeLa-APL cells represent a potentially useful tool in gaining insights into the mode of action of APL, in selecting non-crossresistant APL structural analogues, as well as in investigating and developing methods to prevent resistance to this drug.