NICOTIANAMINE SYNTHASE activity affects nucleolar iron accumulation and impacts rDNA silencing and RNA methylation in Arabidopsis.

In plant cells, a large pool of iron (Fe) is contained in the nucleolus, as well as in chloroplasts and mitochondria. A central determinant for intracellular distribution of Fe is nicotianamine (NA) generated by NICOTIANAMINE SYNTHASE (NAS). Here, we used Arabidopsis thaliana plants with disrupted NAS genes to study the accumulation of nucleolar iron and understand its role in nucleolar functions and more specifically in rRNA gene expression. We found that nas124 triple mutant plants, which contained lower quantities of the iron ligand NA, also contained less iron in the nucleolus. This was concurrent with the expression of normally silenced rRNA genes from nucleolar organizer regions 2 (NOR2). Notably, in nas234 triple mutant plants, which also contained lower quantities of NA, nucleolar iron and rDNA expression were not affected. In contrast, in both nas124 and nas234, specific RNA modifications were differentially regulated in a genotype dependent manner. Taken together, our results highlight the impact of specific NAS activities in RNA gene expression. We discuss the interplay between NA and nucleolar iron with rDNA functional organization and RNA methylation.

Impacts of microplastics and the associated plastisphere on physiological, biochemical, genetic expression and gut microbiota of the filter-feeder amphioxus.

Oceanic plastic pollution is of major concern to marine organisms, especially filter feeders. However, limited is known about the toxic effects of the weathered microplastics instead of the pristine ones. This study evaluates the effects of weathered polystyrene microplastic on a filter-feeder amphioxus under starvation conditions via its exposure to the microplastics previously deployed in the natural seawater allowing for the development of a mature biofilm (so-called plastisphere). The study focused on the integration of physiological, histological, biochemical, molecular, and microbiota impacts on amphioxus. Overall, specific alterations in gene expression of marker genes were observed to be associated with oxidative stresses and immune systems. Negligible impacts were observed on antioxidant biochemical activities and gut microbiota of amphioxus, while we highlighted the potential transfer of 12 bacterial taxa from the plastisphere to the amphioxus gut microbiota. Moreover, the classical perturbation of body shape detected in control animals under starvation conditions (a slim and curved body) but not for amphioxus exposed to microplastic, indicates that the microorganisms colonizing plastics could serve as a nutrient source for this filter-feeder, commitment with the elevated proportions of goblet cell-like structures after the microplastic exposure. The multidisciplinary approach developed in this study underlined the trait of microplastics that acted as vectors for transporting microorganisms from the plastisphere to amphioxus.

Features of the Opportunistic Behaviour of the Marine Bacterium Marinobacter algicola in the Microalga Ostreococcus tauri Phycosphere.

Although interactions between microalgae and bacteria are observed in both natural environment and the laboratory, the modalities of coexistence of bacteria inside microalgae phycospheres in laboratory cultures are mostly unknown. Here, we focused on well-controlled cultures of the model green picoalga Ostreococcus tauri and the most abundant member of its phycosphere, Marinobacter algicola. The prevalence of M. algicola in O. tauri cultures raises questions about how this bacterium maintains itself under laboratory conditions in the microalga culture. The results showed that M. algicola did not promote O. tauri growth in the absence of vitamin B12 while M. algicola depended on O. tauri to grow in synthetic medium, most likely to obtain organic carbon sources provided by the microalgae. M. algicola grew on a range of lipids, including triacylglycerols that are known to be produced by O. tauri in culture during abiotic stress. Genomic screening revealed the absence of genes of two particular modes of quorum-sensing in Marinobacter genomes which refutes the idea that these bacterial communication systems operate in this genus. To date, the 'opportunistic' behaviour of M. algicola in the laboratory is limited to several phytoplanktonic species including Chlorophyta such as O. tauri. This would indicate a preferential occurrence of M. algicola in association with these specific microalgae under optimum laboratory conditions.

Responses to iron oxide and zinc oxide nanoparticles in echinoderm embryos and microalgae: uptake, growth, morphology, and transcriptomic analysis.

We investigated the toxicity of Iron oxide and Zinc oxide engineered nanoparticles (ENPs) on Paracentrotus lividus sea urchin embryos and three species of microalgae. Morphological responses, internalization, and potential impacts of Fe2O3 and ZnO ENPs on physiology and metabolism were assessed. Both types of ENPs affected P. lividus larval development, but ZnO ENPs had a much stronger effect. While growth of the alga Micromonas commoda was severely impaired by both ENPs, Ostreococcus tauri or Nannochloris sp. were unaffected. Transmission electron microscopy showed the internalization of ENPs in sea urchin embryonic cells while only nanoparticle interaction with external membranes was evidenced in microalgae, suggesting that marine organisms react in diverse ways to ENPs. Transcriptome-wide analysis in P. lividus and M. commoda showed that many different physiological pathways were affected, some of which were common to both species, giving insights about the mechanisms underpinning toxic responses.

Virus-host coexistence in phytoplankton through the genomic lens.

Virus-microbe interactions in the ocean are commonly described by "boom and bust" dynamics, whereby a numerically dominant microorganism is lysed and replaced by a virus-resistant one. Here, we isolated a microalga strain and its infective dsDNA virus whose dynamics are characterized instead by parallel growth of both the microalga and the virus. Experimental evolution of clonal lines revealed that this viral production originates from the lysis of a minority of virus-susceptible cells, which are regenerated from resistant cells. Whole-genome sequencing demonstrated that this resistant-susceptible switch involved a large deletion on one chromosome. Mathematical modeling explained how the switch maintains stable microalga-virus population dynamics consistent with their observed growth pattern. Comparative genomics confirmed an ancient origin of this "accordion" chromosome despite a lack of sequence conservation. Together, our results show how dynamic genomic rearrangements may account for a previously overlooked coexistence mechanism in microalgae-virus interactions.

Mantoniella beaufortii and Mantoniella baffinensis sp. nov. (Mamiellales, Mamiellophyceae), two new green algal species from the high arctic1.

Members of the class Mamiellophyceae comprise species that can dominate picophytoplankton diversity in polar waters. Yet, polar species are often morphologically indistinguishable from temperate species, although clearly separated by molecular features. Here we examine four Mamiellophyceae strains from the Canadian Arctic. The 18S rRNA and Internal Transcribed Spacer 2 (ITS2) gene phylogeny place these strains within the family Mamiellaceae (Mamiellales, Mamiellophyceae) in two separate clades of the genus Mantoniella. ITS2 synapomorphies support their placement as two new species, Mantoniella beaufortii and Mantoniella baffinensis. Both species have round green cells with diameter between 3 and 5 µm, one long flagellum and a short flagellum (~1 µm) and are covered by spiderweb-like scales, making both species similar to other Mantoniella species. Morphologically, M. beaufortii and M. baffinensis are most similar to the cosmopolitan M. squamata with only minor differences in scale structure distinguishing them. Screening of global marine metabarcoding data sets indicates M. beaufortii has only been recorded in seawater and sea ice samples from the Arctic, while no environmental barcode matches M. baffinensis. Like other Mamiellophyceae genera that have distinct polar and temperate species, the polar distribution of these new species suggests they are cold or ice-adapted Mantoniella species.

Developmental and comparative transcriptomic identification of iridophore contribution to white barring in clownfish.

Actinopterygian fishes harbor at least eight distinct pigment cell types, leading to a fascinating diversity of colors. Among this diversity, the cellular origin of the white color appears to be linked to several pigment cell types such as iridophores or leucophores. We used the clownfish Amphiprion ocellaris, which has a color pattern consisting of white bars over a darker body, to characterize the pigment cells that underlie the white hue. We observe by electron microscopy that cells in white bars are similar to iridophores. In addition, the transcriptomic signature of clownfish white bars exhibits similarities with that of zebrafish iridophores. We further show by pharmacological treatments that these cells are necessary for the white color. Among the top differentially expressed genes in white skin, we identified several genes (fhl2a, fhl2b, saiyan, gpnmb, and apoD1a) and show that three of them are expressed in iridophores. Finally, we show by CRISPR/Cas9 mutagenesis that these genes are critical for iridophore development in zebrafish. Our analyses provide clues to the genomic underpinning of color diversity and allow identification of new iridophore genes in fish.

CDK13, a Kinase Involved in Pre-mRNA Splicing, Is a Component of the Perinucleolar Compartment.

The perinucleolar compartment (PNC) is a subnuclear stucture forming predominantly in cancer cells; its prevalence positively correlates with metastatic capacity. Although several RNA-binding proteins have been characterized in PNC, the molecular function of this compartment remains unclear. Here we demonstrate that the cyclin-dependent kinase 13 (CDK13) is a newly identified constituent of PNC. CDK13 is a kinase involved in the regulation of gene expression and whose overexpression was found to alter pre-mRNA processing. In this study we show that CDK13 is enriched in PNC and co-localizes all along the cell cycle with the PNC component PTB. In contrast, neither the cyclins K and L, known to associate with CDK13, nor the potential kinase substrates accumulate in PNC. We further show that CDK13 overexpression increases PNC prevalence suggesting that CDK13 may be determinant for PNC formation. This result linked to the finding that CDK13 gene is amplified in different types of cancer indicate that this kinase can contribute to cancer development in human.

Histopathological and ultrastructural studies of a Henneguya species (Myxozoa: Myxosporea) infesting the intestine of Clarias gariepinus from Benin (West Africa).

Fish culture is the best alternative to fill the gap between natural fish catches and estimated needs of populations in animal protein consumption. In West Africa, this goal required to have suitable fishes for aquaculture which are Clariidae and Tilapia. Clarias gariepinus (Clariidae) fetches a higher price than tilapias as it can be sold alive at the market but a high infestation by Henneguya leads to decrease this commercial value. Those reasons lead us to perform studies on seasonal variations, histopathological aspects and life cycle of Henneguya sp. infecting the intestine of C. gariepinus using light and electron microscope. From November 2011 to December 2012, 339 specimens were collected from Ouémé River (Benin) and examined. An overall prevalence of 7.37 % was recorded for plasmodia of Henneguya sp. Parasite occurrence did not vary significantly between seasons (χ(2) = 12.235; df = 3; p > 0.05), nor sexes (χ(2) = 2.992; df = 7; p > 0.05) while differences were significant between classes of weight (χ(2) = 39.929; df = 5; p < 0.05). The highest prevalence was recorded in host ranging from 300 to 374 g. Histopathological analysis showed that the mass continuous development of the plasmodium produced thickening of the intestine wall and compressed neighboring tissues and destroyed villi and smooth muscle layers. The stages of the parasite development including sporogenesis, capsulogenesis, and valvogenesis were asynchronous. Investigations are still running by molecular approaches in order to identify accurately this species.

Chloroplast incorporation and long-term photosynthetic performance through the life cycle in laboratory cultures of Elysia timida (Sacoglossa, Heterobranchia).

INTRODUCTION: The Mediterranean sacoglossan Elysia timida is one of the few sea slug species with the ability to sequester chloroplasts from its food algae and to subsequently store them in a functional state in the digestive gland cells for more than a month, during which time the plastids retain high photosynthetic activity (= long-term retention). Adult E. timida have been described to feed on the unicellular alga Acetabularia acetabulum in their natural environment. The suitability of E. timida as a laboratory model culture system including its food source was studied. RESULTS: In contrast to the literature reporting that juvenile E. timida feed on Cladophora dalmatica first, and later on switch to the adult diet A. acetabulum, the juveniles in this study fed directly on A. acetabulum (young, non-calcified stalks); they did not feed on the various Cladophora spp. (collected from the sea or laboratory culture) offered. This could possibly hint to cryptic speciation with no clear morphological differences, but incipient ecological differentiation. Transmission electron microscopy of chloroplasts from A. acetabulum after initial intake by juvenile E. timida showed different states of degradation - in conglomerations or singularly - and fragments of phagosome membranes, but differed from kleptoplast images of C. dalmatica in juvenile E. timida from the literature. Based on the finding that the whole life cycle of E. timida can be completed with A. acetabulum as the sole food source, a laboratory culture system was established. An experiment with PAM-fluorometry showed that cultured E. timida are also able to store chloroplasts in long-term retention from Acetabularia peniculus, which stems from the Indo-Pacific and is not abundant in the natural environment of E. timida. Variations between three experiment groups indicated potential influences of temperature on photosynthetic capacities. CONCLUSIONS: E. timida is a viable laboratory model system to study photosynthesis in incorporated chloroplasts (kleptoplasts). Capacities of chloroplast incorporation in E. timida were investigated in a closed laboratory culture system with two different chloroplast donors and over extended time periods about threefold longer than previously reported.

A single betaproteobacterium dominates the microbial community of the crambescidine-containing sponge Crambe crambe.

Crambe crambe is a marine sponge that produces high concentrations of the pharmacologically significant pentacyclic guanidine alkaloids (PGAs), Crambescines and Crambescidines. Although bio-mimetic chemical synthesis of PGAs suggests involvement of microorganisms in their biosynthesis, there are conflicting reports on whether bacteria are associated with this sponge or not. Using 16S rRNA gene pyrosequencing we show that the associated bacterial community of C. crambe is dominated by a single bacterial species affiliated to the Betaproteobacteria. Microscopy analysis of sponge tissue sections using a specific probe and in situ hybridization confirmed its dominance in the sponge mesohyl and a single microbial morphology was observed by transmission electron microscopy. If confirmed the presence of a simple bacteria community in C. crambe makes this association a very pertinent model to study sponge-bacteria interactions and should allow further research into the possible implication of bacteria in PGA biosynthesis.

Morphology, genome plasticity, and phylogeny in the genus ostreococcus reveal a cryptic species, O. mediterraneus sp. nov. (Mamiellales, Mamiellophyceae).

Coastal marine waters in many regions worldwide support abundant populations of extremely small (1-3 µm diameter) unicellular eukaryotic green algae, dominant taxa including several species in the class Mamiellophyceae. Their diminutive size conceals surprising levels of genetic diversity and defies classical species' descriptions. We present a detailed analysis within the genus Ostreococcus and show that morphological characteristics cannot be used to describe diversity within this group. Karyotypic analyses of the best-characterized species O. tauri show it to carry two chromosomes that vary in size between individual clonal lines, probably an evolutionarily ancient feature that emerged before species' divergences within the Mamiellales. By using a culturing technique specifically adapted to members of the genus Ostreococcus, we purified >30 clonal lines of a new species, Ostreococcus mediterraneus sp. nov., previously known as Ostreococcus clade D, that has been overlooked in several studies based on PCR-amplification of genetic markers from environment-extracted DNA. Phylogenetic analyses of the S-adenosylmethionine synthetase gene, and of the complete small subunit ribosomal RNA gene, including detailed comparisons of predicted ITS2 (internal transcribed spacer 2) secondary structures, clearly support that this is a separate species. In addition, karyotypic analyses reveal that the chromosomal location of its ribosomal RNA gene cluster differs from other Ostreococcus clades.

Identification and expression analysis of BMP signaling inhibitors genes of the DAN family in amphioxus.

Bone morphogenetic proteins (BMPs) are members of the Transforming Growth Factor-ß (TGF-ß) family implicated in many developmental processes in metazoans such as embryo axes specification. Their wide variety of actions is in part controlled by inhibitors that impede the interaction of BMPs with their specific receptors. Here, we focused our attention on the Differential screening-selected gene Aberrative in Neuroblastoma (DAN) family of inhibitors. Although they are well-characterized in vertebrates, few data are available for this family in other metazoan species. In order to understand the evolution of potential developmental roles of these inhibitors in chordates, we identified the members of this family in the cephalochordate amphioxus, and characterized their expression patterns during embryonic development. Our data suggest that the function of Cerberus/Dand5 subfamily genes is conserved among chordates, whereas Gremlin1/2 and NBL1 subfamily genes seem to have acquired divergent expression patterns in each chordate lineage. On the other hand, the expression of Gremlin in the amphioxus neural plate border during early neurulation strengthens the hypothesis of a conserved neural plate border gene network in chordates.

Amphioxus FGF signaling predicts the acquisition of vertebrate morphological traits.

FGF signaling is one of the few cell-cell signaling pathways conserved among all metazoans. The diversity of FGF gene content among different phyla suggests that evolution of FGF signaling may have participated in generating the current variety of animal forms. Vertebrates possess the greatest number of FGF genes, the functional evolution of which may have been implicated in the acquisition of vertebrate-specific morphological traits. In this study, we have investigated the roles of the FGF signal during embryogenesis of the cephalochordate amphioxus, the best proxy for the chordate ancestor. We first isolate the full FGF gene complement and determine the evolutionary relationships between amphioxus and vertebrate FGFs via phylogenetic and synteny conservation analysis. Using pharmacological treatments, we inhibit the FGF signaling pathway in amphioxus embryos in different time windows. Our results show that the requirement for FGF signaling during gastrulation is a conserved character among chordates, whereas this signal is not necessary for neural induction in amphioxus, in contrast to what is known in vertebrates. We also show that FGF signal, acting through the MAPK pathway, is necessary for the formation of the most anterior somites in amphioxus, whereas more posterior somite formation is not FGF-dependent. This result leads us to propose that modification of the FGF signal function in the anterior paraxial mesoderm in an amphioxus-like vertebrate ancestor might have contributed to the loss of segmentation in the preotic paraxial mesoderm of the vertebrate head.

Acquisition and maintenance of resistance to viruses in eukaryotic phytoplankton populations.

Viruses are known to play a key role in the regulation of eukaryotic phytoplankton population densities; however, little is known about the mechanisms of how they interact with their hosts and how phytoplankton populations mediate their regulations. Viruses are obligate parasites that depend on host cell machinery for their dissemination in the environment (most of the time through host cell lysis that liberates many new particles). But viruses also depend on a reliable host population to carry on their replication before losing their viability. How do hosts cells survive when they coexist with their viruses? We show that clonal lines of three picoeukaryotic green algae (i.e. Bathycoccus sp., Micromonas sp., Ostreococcus tauri) reproducibly acquire resistance to their specific viruses following a round of infection. Our observations show that two mechanisms of resistance may operate in O. tauri. In the first resistant type, viruses can attach to their host cells but no new particles develop. In the second one, O. tauri acquires tolerance to its virus and releases these viruses consistently. These lines maintained their resistance over a 3-year period, irrespective of whether or not they were re-challenged with new viral inoculations. Co-culturing resistant and susceptible lines revealed resistance to be associated with reduced host fitness in terms of growth rate.

Amphioxus Tbx6/16 and Tbx20 embryonic expression patterns reveal ancestral functions in chordates.

T-box transcription factors are found in all metazoans and play diverse roles during embryogenesis. In the cephalochordate amphioxus, nine T-box genes were previously identified. In this work we undertook the analysis of the embryonic expression pattern of Tbx6/16 and Tbx20, the last two T-box genes for which no such data are available. We found that Tbx6/16 is expressed in the unsegmented paraxial mesoderm, in a subpopulation of neurons, and in the tail epidermis. Comparison with the expression patterns of the different vertebrate orthologues indicates a conserved role of those genes in posterior mesoderm formation in chordates. Tbx20 expression is detected in the ventral mesoderm of amphioxus embryos, in cells that are proposed to be precursors of the amphioxus myocardium, in some neurons of the neural tube, and in the pre-oral pit which is thought to be the homologue of the vertebrate adenohypophysis. In vertebrates, Tbx20 is also one of the first genes expressed in the embryonic heart field, suggesting that the function of this gene in heart development has been conserved during chordate evolution.

Integration of light signals by the retinoblastoma pathway in the control of S phase entry in the picophytoplanktonic cell Ostreococcus.

Although the decision to proceed through cell division depends largely on the metabolic status or the size of the cell, the timing of cell division is often set by internal clocks such as the circadian clock. Light is a major cue for circadian clock entrainment, and for photosynthetic organisms it is also the main source of energy supporting cell growth prior to cell division. Little is known about how light signals are integrated in the control of S phase entry. Here, we present an integrated study of light-dependent regulation of cell division in the marine green alga Ostreococcus. During early G1, the main genes of cell division were transcribed independently of the amount of light, and the timing of S phase did not occur prior to 6 hours after dawn. In contrast S phase commitment and the translation of a G1 A-type cyclin were dependent on the amount of light in a cAMP-dependent manner. CyclinA was shown to interact with the Retinoblastoma (Rb) protein during S phase. Down-regulating Rb bypassed the requirement for CyclinA and cAMP without altering the timing of S phase. Overexpression of CyclinA overrode the cAMP-dependent control of S phase entry and led to early cell division. Therefore, the Rb pathway appears to integrate light signals in the control of S phase entry in Ostreococcus, though differential transcriptional and posttranscriptional regulations of a G1 A-type cyclin. Furthermore, commitment to S phase depends on a cAMP pathway, which regulates the synthesis of CyclinA. We discuss the relative involvements of the metabolic and time/clock signals in the photoperiodic control of cell division.

Gallaecimonas pentaromativorans gen. nov., sp. nov., a bacterium carrying 16S rRNA gene heterogeneity and able to degrade high-molecular-mass polycyclic aromatic hydrocarbons.

A Gram-negative, rod-shaped, halotolerant bacterium, designated strain CEE_131(T), which degraded high-molecular-mass polycyclic aromatic hydrocarbons of four and five rings, was isolated from intertidal sediment of Corcubion Ria in Cee, A Coruña, Spain. Direct sequencing showed ambiguities and suggested heterogeneity. Cloned 16S rRNA gene sequence PCR products yielded five different sequences varying at five positions. Strain CEE_131(T) showed rather distant relationships to its phylogenetically closest neighbours, including the genera Rheinheimera and Serratia , exhibiting 91 % sequence similarity with Rheinheimera perlucida BA131(T) and Serratia proteamaculans subsp. quinovora DSM 4597(T). The major fatty acids were C(16 : 1 )omega7c, C(16 : 0) and C(18 : 1)omega7c. The DNA G+C content was 41.7 mol%. On the basis of these distinct phenotypic and genotypic characteristics, strain CEE_131(T) is considered to represent a novel species in a new genus in the class Gammaproteobacteria, for which the name Gallaecimonas pentaromativorans gen. nov., sp. nov. is proposed. The type strain is CEE_131(T) (=DSM 21945(T)=CECT 7479(T)).

Ultraviolet radiation induces structural and chromatin damage in Mediterranean sea-urchin spermatozoa.

There is growing concern about the effects of enhanced levels of solar ultraviolet radiation on the living components of the biosphere (i.e. cancer, loss of biodiversity and productivity, etc.). In shallow coastal environments, many benthic species release their gametes directly in the water column where fertilisation occurs and the planktonic larvae remain for several weeks. Any effects on these early life stages could significantly impair reproductive input or alter the fitness of the community. The purpose of this paper is to provide new insights into the mechanisms of UV toxicity on sea-urchin spermatozoa in a cytological context, and to address the question of the potential ecological consequences of the damage. The Mediterranean sea-urchin Sphaerechinus granularis (Lamarck) was chosen as a model to study the effects of ecologically relevant doses of UV-R on the spermatozoa of marine invertebrates. Structural damage was visualised by use of transmission electron microscopy and the single-cell gel electrophoresis (Comet) assay was used to assess chromatin integrity in spermatozoa. The present results provide experimental evidence that irradiation with UV induces structural and chromatin damage in sea-urchin sperm. Almost 90% of spermatozoa exhibited morphological alterations and DNA strand breakage increased 2-fold. The observed alterations of the acrosome, plasma membrane and mitochondria can explain the concomitant impairment of fertilisation (23% decrease of fertilisation rate), which in turn may affect reproductive success. On the other hand, how DNA damage and fertilisation rate correlate remains unclear; however, when not repaired genetic lesions can lead to abnormal development and/or the transmission of heritable damage. The 3-fold decrease of the frequency of 2-celled embryos indicates a delay or inhibition of the first cell division, which may be ascribed to impairment of nuclear chromatin and/or other cellular targets.

Urochordate histoincompatible interactions activate vertebrate-like coagulation system components.

The colonial ascidian Botryllus schlosseri expresses a unique allorecognition system. When two histoincompatible Botryllus colonies come into direct contact, they develop an inflammatory-like rejection response. A surprising high number of vertebrates' coagulation genes and coagulation-related domains were disclosed in a cDNA library of differentially expressed sequence tags (ESTs), prepared for this allorejection process. Serine proteases, especially from the trypsin family, were highly represented among Botryllus library ortholgues and its "molecular function" gene ontology analysis. These, together with the built-up clot-like lesions in the interaction area, led us to further test whether a vertebrate-like clotting system participates in Botryllus innate immunity. Three morphologically distinct clot types (points of rejection; POR) were followed. We demonstrated the specific expression of nine coagulation orthologue transcripts in Botryllus rejection processes and effects of the anti-coagulant heparin on POR formation and heartbeats. In situ hybridization of fibrinogen and von Willebrand factor orthologues elucidated enhanced expression patterns specific to histoincompatible reactions as well as common expressions not augmented by innate immunity. Immunohistochemistry for fibrinogen revealed, in naïve and immune challenged colonies alike, specific antibody binding to a small population of Botryllus compartment cells. Altogether, molecular, physiological and morphological outcomes suggest the involvement of vertebrates-like coagulation elements in urochordate immunity, not assigned with vasculature injury.