Molecular profiling of sponge deflation reveals an ancient relaxant-inflammatory response

A hallmark of animals is the coordination of whole-body movement. Neurons and muscles are central to this, yet coordinated movements also exist in sponges that lack these cell types. Sponges are sessile animals with a complex canal system for filter-feeding. They undergo whole-body movements resembling "contractions" that lead to canal closure and water expulsion. Here, we combine live 3D optical coherence microscopy, pharmacology, and functional proteomics to elucidate the sequence and detail of shape changes, the tissues and molecular physiology involved, and the control of these movements. Morphometric analysis and targeted perturbation suggest that the movement is driven by the relaxation of actomyosin stress fibers in epithelial canal cells, which leads to whole-body deflation via collapse of the incurrent and expansion of the excurrent canal system. Thermal proteome profiling and quantitative phosphoproteomics confirm the control of cellular relaxation by an Akt/NO/PKG/PKA pathway. Agitation-induced deflation leads to differential phosphorylation of proteins forming epithelial cell junctions, implying their mechanosensitive role. Unexpectedly, untargeted metabolomics detect a concomitant decrease in antioxidant molecules during deflation, reflecting an increase in reactive oxygen species. Together with the secretion of proteinases, cytokines, and granulin, this indicates an inflammation-like state of the deflating sponge reminiscent of vascular endothelial cells experiencing oscillatory shear stress. These results suggest the conservation of an ancient relaxant-inflammatory response of perturbed fluid-carrying systems in animals and offer a possible mechanism for whole-body coordination through diffusible paracrine signals and mechanotransduction.

Regeneration in calcareous sponge relies on 'purse-string' mechanism and the rearrangements of actin cytoskeleton

The crucial step in any regeneration process is epithelization, i.e. the restoration of an epithelium structural and functional integrity. Epithelization requires cytoskeletal rearrangements, primarily of actin filaments and microtubules. Sponges (phylum Porifera) are early branching metazoans with pronounced regenerative abilities. Calcareous sponges have a unique step during regeneration: the formation of a temporary structure, called regenerative membrane which initially covers a wound. It forms due to the morphallactic rearrangements of exopinaco- and choanoderm epithelial-like layers. The current study quantitatively evaluates morphological changes and characterises underlying actin cytoskeleton rearrangements during regenerative membrane formation in asconoid calcareous sponge Leucosolenia variabilis through a combination of time-lapse imaging, immunocytochemistry, and confocal laser scanning microscopy. Regenerative membrane formation has non-linear stochastic dynamics with numerous fluctuations. The pinacocytes at the leading edge of regenerative membrane form a contractile actomyosin cable. Regenerative membrane formation either depends on its contraction or being coordinated through it. The cell morphology changes significantly during regenerative membrane formation. Exopinacocytes flatten, their area increases, while circularity decreases. Choanocytes transdifferentiate into endopinacocytes, losing microvillar collar and flagellum. Their area increases and circularity decreases. Subsequent redifferentiation of endopinacocytes into choanocytes is accompanied by inverse changes in cell morphology. All transformations rely on actin filament rearrangements similar to those characteristic of bilaterian animals. Altogether, we provide here a qualitative and quantitative description of cell transformations during reparative epithelial morphogenesis in a calcareous sponge.

Cell contractility in early animal evolution

Tissue deformation mediated by collective cell contractility is a signature characteristic of animals. In most animals, fast and reversible contractions of muscle cells mediate behavior, while slow and irreversible contractions of epithelial or mesenchymal cells play a key role in morphogenesis. Animal tissue contractility relies on the activity of the actin/myosin II complex (together referred to as 'actomyosin'), an ancient and versatile molecular machinery that performs a broad range of functions in development and physiology. This review synthesizes emerging insights from morphological and molecular studies into the evolutionary history of animal contractile tissue. The most ancient functions of actomyosin are cell crawling and cytokinesis, which are found in a wide variety of unicellular eukaryotes and in individual metazoan cells. Another contractile functional module, apical constriction, is universal in metazoans and shared with choanoflagellates, their closest known living relatives. The evolution of animal contractile tissue involved two key innovations: firstly, the ability to coordinate and integrate actomyosin assembly across multiple cells, notably to generate supracellular cables, which ensure tissue integrity but also allow coordinated morphogenesis and movements at the organism scale; and secondly, the evolution of dedicated contractile cell types for adult movement, belonging to two broad categories respectively defined by the expression of the fast (striated-type) and slow (smooth/non-muscle-type) myosin II paralogs. Both contractile cell types ancestrally resembled generic contractile epithelial or mesenchymal cells and might have played a versatile role in both behavior and morphogenesis. Modern animal contractile cells span a continuum between unspecialized contractile epithelia (which underlie behavior in modern placozoans), epithelia with supracellular actomyosin cables (found in modern sponges), epitheliomuscular tissues (with a concentration of actomyosin cables in basal processes, for example in sea anemones), and specialized muscle tissue that has lost most or all epithelial properties (as in ctenophores, jellyfish and bilaterians). Recent studies in a broad range of metazoans have begun to reveal the molecular basis of these transitions, powered by the elaboration of the contractile apparatus and the evolution of 'core regulatory complexes' of transcription factors specifying contractile cell identity.

Respiration kinetics and allometric scaling in the demosponge Halichondria panicea

BACKGROUND

The aquiferous system in sponges represents one of the simplest circulatory systems used by animals for the internal uptake and distribution of oxygen and metabolic substrates. Its modular organization enables sponges to metabolically scale with size differently than animals with an internal circulatory system. In this case, metabolic rate is typically limited by surface to volume constraints to maintain an efficient supply of oxygen and food. Here, we consider the linkeage between oxygen concentration, the respiration rates of sponges and sponge size.

RESULTS

We explored respiration kinetics for individuals of the demosponge Halichondria panicea with varying numbers of aquiferous modules (nmodules = 1-102). From this work we establish relationships between the sponge size, module number, maximum respiration rate (Rmax) and the half-saturation constant, Km, which is the oxygen concentration producing half of the maximum respiration rate, Rmax. We found that the nmodules in H. panicea scales consistently with sponge volume (Vsp) and that Rmax increased with sponge size with a proportionality > 1. Conversly, we found a lack of correlation between Km and sponge body size suggesting that oxygen concentration does not control the size of sponges.

CONCLUSIONS

The present study reveals that the addition of aquiferous modules (with a mean volume of 1.59 ± 0.22 mL) enables H. panicea in particular, and likely demosponges in general, to grow far beyond constraints limiting the size of their component modules and independent of ambient oxygen levels.

Molecular profiling of sponge deflation reveals an ancient relaxant-inflammatory response

A hallmark of animals is the coordination of whole-body movement. Neurons and muscles are central to this, yet coordinated movements also exist in sponges that lack these cell types. Sponges are sessile animals with a complex canal system for filter-feeding. They undergo whole-body movements resembling "contractions" that lead to canal closure and water expulsion. Here, we combine 3D optical coherence microscopy, pharmacology, and functional proteomics to elucidate anatomy, molecular physiology, and control of these movements. We find them driven by the relaxation of actomyosin stress fibers in epithelial canal cells, which leads to whole-body deflation via collapse of the incurrent and expansion of the excurrent system, controlled by an Akt/NO/PKG/A pathway. A concomitant increase in reactive oxygen species and secretion of proteinases and cytokines indicate an inflammation-like state reminiscent of vascular endothelial cells experiencing oscillatory shear stress. This suggests an ancient relaxant-inflammatory response of perturbed fluid-carrying systems in animals.

Cross-phyla protein annotation by structural prediction and alignment

BACKGROUND

Protein annotation is a major goal in molecular biology, yet experimentally determined knowledge is typically limited to a few model organisms. In non-model species, the sequence-based prediction of gene orthology can be used to infer protein identity; however, this approach loses predictive power at longer evolutionary distances. Here we propose a workflow for protein annotation using structural similarity, exploiting the fact that similar protein structures often reflect homology and are more conserved than protein sequences.

RESULTS

We propose a workflow of openly available tools for the functional annotation of proteins via structural similarity (MorF: MorphologFinder) and use it to annotate the complete proteome of a sponge. Sponges are highly relevant for inferring the early history of animals, yet their proteomes remain sparsely annotated. MorF accurately predicts the functions of proteins with known homology in [Formula: see text] cases and annotates an additional [Formula: see text] of the proteome beyond standard sequence-based methods. We uncover new functions for sponge cell types, including extensive FGF, TGF, and Ephrin signaling in sponge epithelia, and redox metabolism and control in myopeptidocytes. Notably, we also annotate genes specific to the enigmatic sponge mesocytes, proposing they function to digest cell walls.

CONCLUSIONS

Our work demonstrates that structural similarity is a powerful approach that complements and extends sequence similarity searches to identify homologous proteins over long evolutionary distances. We anticipate this will be a powerful approach that boosts discovery in numerous -omics datasets, especially for non-model organisms.

The contraction-expansion behaviour in the demosponge Tethya wilhelma is light controlled and follows a diurnal rhythm

Sponges (phylum Porifera) are metazoans which lack muscles and nerve cells, yet perform coordinated behaviours such as whole-body contractions. Previous studies indicate diurnal variability in both the number of contractions and the expression of circadian clock genes. Here, we show that diurnal patterns are present in the contraction-expansion behaviour of the demosponge Tethya wilhelma, by using infrared videography and a simulated night/day cycle including sunrise and sunset mimics. In addition, we show that this behaviour is at least strongly influenced by ambient light intensity and therefore indicates light-sensing capabilities in this sponge species. This is supported by our finding that T. wilhelma consistently contracts at sunrise, and that this pattern disappears both when the sponge is kept in constant darkness and when it is in constant light.

Sponges sneeze mucus to shed particulate waste from their seawater inlet pores

Sponges, among the oldest extant multicellular organisms on Earth,¹ play a key role in the cycling of nutrients in many aquatic ecosystems.2, 3, 4, 5 They need to employ strategies to prevent clogging of their internal filter system by solid wastes,6, 7, 8 but self-cleaning mechanisms are largely unknown. It is commonly assumed that sponges remove solid waste with the outflowing water through distinct outflow openings (oscula).^3,9 Here, we present time-lapse video footage and analyses of sponge waste revealing a completely different mechanism of particle removal in the Caribbean tube sponge Aplysina archeri. This sponge actively moves particle-trapping mucus against the direction of its internal water flow and ejects it into the surrounding water from its seawater inlet pores (ostia) through periodic surface contractions that have been described earlier as “sneezing.”^10,11 Visually, it appears as if the sponge is continuously streaming mucus-embedded particles and sneezes to shed this particulate waste, resulting in a notable flux of detritus that is actively consumed by sponge-associated fauna. The new data are used to estimate production of detritus for this abundant sponge on Caribbean coral reefs. Last, we discuss why waste removal from the sponge inhalant pores may be a common feature among sponges and compare the process in sponges to equivalent mechanisms of mucus transport in other animals, including humans.

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The tube sponge Aplysina archeri moves mucus against its internal feeding current

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Particulate waste is trapped by the mucus and aggregates on the sponge’s surface

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Mucus and waste are sneezed into the environment or fed upon by associated fauna

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Mucus travels too slowly for known ciliary transport, suggesting a novel mechanism

MRTF specifies a muscle-like contractile module in Porifera

Muscle-based movement is a hallmark of animal biology, but the evolutionary origins of myocytes are unknown. Although believed to lack muscles, sponges (Porifera) are capable of coordinated whole-body contractions that purge debris from internal water canals. This behavior has been observed for decades, but their contractile tissues remain uncharacterized with respect to their ultrastructure, regulation, and development. We examine the sponge Ephydatia muelleri and find tissue-wide organization of a contractile module composed of actin, striated-muscle myosin II, and transgelin, and that contractions are regulated by the release of internal Ca²⁺ stores upstream of the myosin-light-chain-kinase (MLCK) pathway. The development of this contractile module appears to involve myocardin-related transcription factor (MRTF) as part of an environmentally inducible transcriptional complex that also functions in muscle development, plasticity, and regeneration. As an actin-regulated force-sensor, MRTF-activity offers a mechanism for how the contractile tissues that line water canals can dynamically remodel in response to flow and can re-form normally from stem-cells in the absence of the intrinsic spatial cues typical of animal embryogenesis. We conclude that the contractile module of sponge tissues shares elements of homology with contractile tissues in other animals, including muscles, indicating descent from a common, multifunctional tissue in the animal stem-lineage.

Myocytes are a key cell type that enable animal movement, but their evolutionary origins remain unclear. Colgren and Nichols describe molecular and functional similarities between a contractile module in tissues of a sponge and muscle tissues in other animals, indicating a common evolutionary origin.

Profiling cellular diversity in sponges informs animal cell type and nervous system evolution

[Figure: see text].

The Evolutionary Assembly of Neuronal Machinery

Neurons are highly specialized cells equipped with a sophisticated molecular machinery for the reception, integration, conduction and distribution of information. The evolutionary origin of neurons remains unsolved. How did novel and pre-existing proteins assemble into the complex machinery of the synapse and of the apparatus conducting current along the neuron? In this review, the step-wise assembly of functional modules in neuron evolution serves as a paradigm for the emergence and modification of molecular machinery in the evolution of cell types in multicellular organisms. The pre-synaptic machinery emerged through modification of calcium-regulated large vesicle release, while the postsynaptic machinery has different origins: the glutamatergic postsynapse originated through the fusion of a sensory signaling module and a module for filopodial outgrowth, while the GABAergic postsynapse incorporated an ancient actin regulatory module. The synaptic junction, in turn, is built around two adhesion modules controlled by phosphorylation, which resemble septate and adherens junctions. Finally, neuronal action potentials emerged via a series of duplications and modifications of voltage-gated ion channels. Based on these origins, key molecular innovations are identified that led to the birth of the first neuron in animal evolution.

The developmental biology of Charnia and the eumetazoan affinity of the Ediacaran rangeomorphs

Molecular timescales estimate that early animal lineages diverged tens of millions of years before their earliest unequivocal fossil evidence. The Ediacaran macrobiota (~574 to 538 million years ago) are largely eschewed from this debate, primarily due to their extreme phylogenetic uncertainty, but remain germane. We characterize the development of Charnia masoni and establish the affinity of rangeomorphs, among the oldest and most enigmatic components of the Ediacaran macrobiota. We provide the first direct evidence for the internal interconnected nature of rangeomorphs and show that Charnia was constructed of repeated branches that derived successively from pre-existing branches. We find homology and rationalize morphogenesis between disparate rangeomorph taxa, before producing a phylogenetic analysis, resolving Charnia as a stem-eumetazoan and expanding the anatomical disparity of that group to include a long-extinct bodyplan. These data bring competing records of early animal evolution into closer agreement, reformulating our understanding of the evolutionary emergence of animal bodyplans.

Glycine as a signaling molecule and chemoattractant in Trichoplax (Placozoa): insights into the early evolution of neurotransmitters

The origin and early evolution of neurotransmitter signaling in animals are unclear due to limited comparative information, primarily about prebilaterian animals. Here, we performed the comparative survey of signal molecules in placozoans - the simplest known free-living animals without canonical synapses, but with complex behaviors. First, using capillary electrophoresis with laser-induced fluorescence detection, we performed microchemical analyses of transmitter candidates in Trichoplax adhaerens - the classical reference species in comparative biology. We showed that the endogenous level of glycine (about 3 mM) was significantly higher than for other candidates such as L-glutamate, L-aspartate, or gamma-aminobutyric acid. Neither serotonin nor dopamine were detected. The absolute glycine concentrations in Trichoplax were even higher than we measured in ctenophores (Beroe) and cnidarians (Aequorea). We found that at millimolar concentrations of glycine (similar to the endogenous level), induced muscle-like contractions in free behaving animals. But after long incubation (24 h), 10 M of glycine could induce cytotoxicity and cell dissociation. In contrast, micromolar concentrations (10-10 M) increased Trichoplax ciliated locomotion, suggesting that glycine might act as an endogenous signal molecule. However, we showed than glycine (10 M) can also be a chemoattractant (a guiding factor for food sources), and therefore, act as the exogenous signal. These findings provide an evolutionary base for the origin of transmitters as a result of the interplay between exogenous and endogenous signaling systems early in animal evolution.

The Diversity of Muscles and Their Regenerative Potential across Animals

Cells with contractile functions are present in almost all metazoans, and so are the related processes of muscle homeostasis and regeneration. Regeneration itself is a complex process unevenly spread across metazoans that ranges from full-body regeneration to partial reconstruction of damaged organs or body tissues, including muscles. The cellular and molecular mechanisms involved in regenerative processes can be homologous, co-opted, and/or evolved independently. By comparing the mechanisms of muscle homeostasis and regeneration throughout the diversity of animal body-plans and life cycles, it is possible to identify conserved and divergent cellular and molecular mechanisms underlying muscle plasticity. In this review we aim at providing an overview of muscle regeneration studies in metazoans, highlighting the major regenerative strategies and molecular pathways involved. By gathering these findings, we wish to advocate a comparative and evolutionary approach to prompt a wider use of “non-canonical” animal models for molecular and even pharmacological studies in the field of muscle regeneration.

Light-regulated collective contractility in a multicellular choanoflagellate

Collective cell contractions that generate global tissue deformations are a signature feature of animal movement and morphogenesis. However, the origin of collective contractility in animals remains unclear. While surveying the Caribbean island of Curaçao for choanoflagellates, the closest living relatives of animals, we isolated a previously undescribed species (here named Choanoeca flexa sp. nov.) that forms multicellular cup-shaped colonies. The colonies rapidly invert their curvature in response to changing light levels, which they detect through a rhodopsin-cyclic guanosine monophosphate pathway. Inversion requires actomyosin-mediated apical contractility and allows alternation between feeding and swimming behavior. C. flexa thus rapidly converts sensory inputs directly into multicellular contractions. These findings may inform reconstructions of hypothesized animal ancestors that existed before the evolution of specialized sensory and contractile cells.

Evolution of glial wrapping: A new hypothesis

Animals are able to move and react in numerous ways to external stimuli. Thus, environmental stimuli need to be detected, information must be processed and finally an output decision must be transmitted to the musculature to get the animal moving. All these processes depend on the nervous system which comprises an intricate neuronal network and many glial cells. In the last decades, a neurono-centric view on nervous system function channeled most of the scientific interest toward the analysis of neurons and neuronal functions. Neurons appeared early in animal evolution and the main principles of neuronal function from synaptic transmission to propagation of action potentials are conserved during evolution. In contrast, not much is known on the evolution of glial cells that were initially considered merely as static support cells. Although it is now accepted that glial cells have an equally important contribution as their neuronal counterpart to nervous system function, their evolutionary origin is unknown. Did glial cells appear several times during evolution? What were the first roles glial cells had to fulfil in the nervous system? What triggered the formation of the amazing diversity of glial morphologies and functions? Is there a possible mechanism that might explain the appearance of complex structures such as myelin in vertebrates? Here, we postulate a common evolutionary origin of glia and depict a number of selective forces that might have paved the way from a simple supporting cell to a wrapping and myelin forming glial cell.

Sponge Behavior and the Chemical Basis of Responses: A Post-Genomic View

Sponges perceive and respond to a range of stimuli. How they do this is still difficult to pin down despite now having transcriptomes and genomes of an array of species. Here we evaluate the current understanding of sponge behavior and present new observations on sponge activity in situ. We also explore biosynthesis pathways available to sponges from data in genomes/transcriptomes of sponges and other non-bilaterians with a focus on exploring the role of chemical signaling pathways mediating sponge behavior and how such chemical signal pathways may have evolved. Sponge larvae respond to light but opsins are not used, nor is there a common photoreceptor molecule or mechanism used across sponge groups. Other cues are gravity and chemicals. In situ recordings of behavior show that both shallow and deep-water sponges move a lot over minutes and hours, and correlation of behavior with temperature, pressure, oxygen, and water movement suggests that at least one sponge responds to changes in atmospheric pressure. The sensors for these cues as far as we know are individual cells and, except in the case of electrical signaling in Hexactinellida, these most likely act as independent effectors, generating a whole-body reaction by the global reach of the stimulus to all parts of the animal. We found no evidence for use of conventional neurotransmitters such as serotonin and dopamine. Intriguingly, some chemicals synthesized by symbiont microbes could mean other more complex signaling occurs, but how that interplay might happen is not understood. Our review suggests chemical signaling pathways found in sponges do not reflect loss of a more complex set.

Bodily Complexity: Integrated Multicellular Organizations for Contraction-Based Motility

Compared to other forms of multicellularity, the animal case is unique. Animals-barring some exceptions-consist of collections of cells that are connected and integrated to such an extent that these collectives act as unitary, large free-moving entities capable of sensing macroscopic properties and events. This animal configuration is so well-known that it is often taken as a natural one that 'must' have evolved, given environmental conditions that make large free-moving units 'obviously' adaptive. Here we question the seemingly evolutionary inevitableness of animals and introduce a thesis of bodily complexity: The multicellular organization characteristic for typical animals requires the integration of a multitude of intrinsic bodily features between its sensorimotor, physiological, and developmental aspects, and the related contraction-based tissue- and cellular-level events and processes. The evolutionary road toward this bodily complexity involves, we argue, various intermediate organizational steps that accompany and support the wider transition from cilia-based to contraction/muscle-based motility, and which remain insufficiently acknowledged. Here, we stress the crucial and specific role played by muscle-based and myoepithelial tissue contraction-acting as a physical platform for organizing both the multicellular transmission of mechanical forces and multicellular signaling-as key foundation of animal motility, sensing and maintenance, and development. We illustrate and discuss these bodily features in the context of the four basal animal phyla-Porifera, Ctenophores, Placozoans, and Cnidarians-that split off before the bilaterians, a supergroup that incorporates all complex animals.

The significance of sponges for comparative studies of developmental evolution

Sponges, ctenophores, placozoans, and cnidarians have key evolutionary significance in that they bracket the time interval during which organized animal tissues were first assembled, fundamental cell types originated (e.g., neurons and myocytes), and developmental patterning mechanisms evolved. Sponges in particular have often been viewed as living surrogates for early animal ancestors, largely due to similarities between their feeding cells (choanocytes) with choanoflagellates, the unicellular/colony-forming sister group to animals. Here, we evaluate these claims and highlight aspects of sponge biology with comparative value for understanding developmental evolution, irrespective of the purported antiquity of their body plan. Specifically, we argue that sponges strike a different balance between patterning and plasticity than other animals, and that environmental inputs may have prominence over genetically regulated developmental mechanisms. We then present a case study to illustrate how contractile epithelia in sponges can help unravel the complex ancestry of an ancient animal cell type, myocytes, which sponges lack. Sponges represent hundreds of millions of years of largely unexamined evolutionary experimentation within animals. Their phylogenetic placement lends them key significance for learning about the past, and their divergent biology challenges current views about the scope of animal cell and developmental biology. This article is characterized under: Comparative Development and Evolution > Evolutionary Novelties Comparative Development and Evolution > Body Plan Evolution.

Early animal evolution: a morphologist's view

Two hypotheses for the early radiation of the metazoans are vividly discussed in recent phylogenomic studies, the 'Porifera-first' hypothesis, which places the poriferans as the sister group of all other metazoans, and the 'Ctenophora-first' hypothesis, which places the ctenophores as the sister group to all other metazoans. It has been suggested that an analysis of morphological characters (including specific molecules) could throw additional light on the controversy, and this is the aim of this paper. Both hypotheses imply independent evolution of nervous systems in Planulozoa and Ctenophora. The Porifera-first hypothesis implies no homoplasies or losses of major characters. The Ctenophora-first hypothesis shows no important synapomorphies of Porifera, Planulozoa and Placozoa. It implies either independent evolution, in Planulozoa and Ctenophora, of a new digestive system with a gut with extracellular digestion, which enables feeding on larger organisms, or the subsequent loss of this new gut in the Poriferans (and the re-evolution of the collar complex). The major losses implied in the Ctenophora-first theory show absolutely no adaptational advantages. Thus, morphology gives very strong support for the Porifera-first hypothesis.

Evidence of Signaling and Adhesion Roles for β-Catenin in the Sponge Ephydatia muelleri

β-Catenin acts as a transcriptional coactivator in the Wnt/β-catenin signaling pathway and a cytoplasmic effector in cadherin-based cell adhesion. These functions are ancient within animals, but the earliest steps in β-catenin evolution remain unresolved due to limited data from key lineages-sponges, ctenophores, and placozoans. Previous studies in sponges have characterized β-catenin expression dynamics and used GSK3B antagonists to ectopically activate the Wnt/β-catenin pathway; both approaches rely upon untested assumptions about the conservation of β-catenin function and regulation in sponges. Here, we test these assumptions using an antibody raised against β-catenin from the sponge Ephydatia muelleri. We find that cadherin-complex genes coprecipitate with endogenous Em β-catenin from cell lysates, but that Wnt pathway components do not. However, through immunostaining we detect both cell boundary and nuclear populations, and we find evidence that Em β-catenin is a conserved substrate of GSK3B. Collectively, these data support conserved roles for Em β-catenin in both cell adhesion and Wnt signaling. Additionally, we find evidence for an Em β-catenin population associated with the distal ends of F-actin stress fibers in apparent cell-substrate adhesion structures that resemble focal adhesions. This finding suggests a fundamental difference in the adhesion properties of sponge tissues relative to other animals, in which the adhesion functions of β-catenin are typically restricted to cell-cell adhesions.

Anatomy and ultrastructure of the tropical sponge Cladocroce caelum (Haplosclerida, Demospongiae)

The main characteristic of sponges (Porifera) is the presence of the aquiferous system-a system formed by canals and choanocyte chambers, in which the sponges carry out most of their physiological functions. Despite of the importance for the biology of the group, the knowledge about this structure is still incipient, even when morphological investigations are taken in account. Here, we investigated the anatomy and ultrastructure of the tropical demosponge Cladocroce caelum (Haplosclerida, Demospongiae) using light and electron microscopy. In the studied region, specimens of this species were repent or repent-branched, possessing one to several oscula. A uniform and reduced atrium was found just below each osculum. There was a thin ectosome and the choanosome presented meager mesohyl, but a high number of choanocyte chambers. The choanocyte chambers were rounded, and, as in other haplosclerids, they are found separated from the mesohyl by endopinacocytes, "hanging" in the inhalant canals. Even though the utility of the general organization of the aquiferous system has been advocated as a possible tool to understand the phylogeny of the group, we found that these characters might not be as useful as expected. The size of the particles ingested by the sponge and the amount of bacteria to sustain their bodies are discussed. In addition, we found that the density of choanocyte chambers was reduced when the specimens were carrying out the spermatogenesis, indicating that the reproduction may impair the filtering activity of the sponge. Our findings consist in a first step to better comprehend the physiology, development, and adaptation to the environmental conditions where the species is found.

Ultrafast epithelial contractions provide insights into contraction speed limits and tissue integrity

By definition of multicellularity, all animals need to keep their cells attached and intact, despite internal and external forces. Cohesion between epithelial cells provides this key feature. To better understand fundamental limits of this cohesion, we study the epithelium mechanics of an ultrathin (∼25 μm) primitive marine animal Trichoplax adhaerens, composed essentially of two flat epithelial layers. With no known extracellular matrix and no nerves or muscles, T. adhaerens has been claimed to be the "simplest known living animal," yet is still capable of coordinated locomotion and behavior. Here we report the discovery of the fastest epithelial cellular contractions known in any metazoan, to be found in T. adhaerens dorsal epithelium (50% shrinkage of apical cell area within one second, at least an order of magnitude faster than other known examples). Live imaging reveals emergent contractile patterns that are mostly sporadic single-cell events, but also include propagating contraction waves across the tissue. We show that cell contraction speed can be explained by current models of nonmuscle actin-myosin bundles without load, while the tissue architecture and unique mechanical properties are softening the tissue, minimizing the load on a contracting cell. We propose a hypothesis, in which the physiological role of the contraction dynamics is to resist external stresses while avoiding tissue rupture ("active cohesion"), a concept that can be further applied to engineering of active materials.

Analysis of a vinculin homolog in a sponge (phylum Porifera) reveals that vertebrate-like cell adhesions emerged early in animal evolution

The evolution of cell-adhesion mechanisms in animals facilitated the assembly of organized multicellular tissues. Studies in traditional animal models have revealed two predominant adhesion structures, the adherens junction (AJ) and focal adhesions (FAs), which are involved in the attachment of neighboring cells to each other and to the secreted extracellular matrix (ECM), respectively. The AJ (containing cadherins and catenins) and FAs (comprising integrins, talin, and paxillin) differ in protein composition, but both junctions contain the actin-binding protein vinculin. The near ubiquity of these structures in animals suggests that AJ and FAs evolved early, possibly coincident with multicellularity. However, a challenge to this perspective is that previous studies of sponges-a divergent animal lineage-indicate that their tissues are organized primarily by an alternative, sponge-specific cell-adhesion mechanism called "aggregation factor." In this study, we examined the structure, biochemical properties, and tissue localization of a vinculin ortholog in the sponge Oscarella pearsei (Op). Our results indicate that Op vinculin localizes to both cell-cell and cell-ECM contacts and has biochemical and structural properties similar to those of vertebrate vinculin. We propose that Op vinculin played a role in cell adhesion and tissue organization in the last common ancestor of sponges and other animals. These findings provide compelling evidence that sponge tissues are indeed organized like epithelia in other animals and support the notion that AJ- and FA-like structures extend to the earliest periods of animal evolution.

Early metazoan cell type diversity and the evolution of multicellular gene regulation

A hallmark of metazoan evolution is the emergence of genomic mechanisms that implement cell type-specific functions. However, the evolution of metazoan cell types and their underlying gene regulatory programs remain largely uncharacterized. Here, we use whole-organism single-cell RNA-seq to map cell type-specific transcription in Porifera (sponges), Ctenophora (comb jellies) and Placozoa species. We describe the repertoires of cell types in these non-bilaterian animals, uncovering diverse instances of previously unknown molecular signatures, such as multiple types of peptidergic cells in Placozoa. Analysis of the regulatory programs of these cell types reveal variable levels of complexity. In placozoans and poriferans, sequence motifs in the promoters are predictive of cell type-specific programs. In contrast, the generation of a higher diversity of cell types in ctenophores is associated to lower specificity of promoter sequences and to the existence of distal regulatory elements. Our findings demonstrate that metazoan cell types can be defined by networks of TFs and proximal promoters, and indicate that further genome regulatory complexity may be required for more diverse cell type repertoires.

Stolonial Movement: A New Type of Whole-Organism Behavior in Porifera

Sponges (phylum Porifera) traditionally are represented as inactive, sessile filter-feeding animals devoid of any behavior except filtering activity. However, different time-lapse techniques demonstrate that sponges are able to show a wide range of coordinated but slow whole-organism behavior. The present study concerns a peculiar type of such behavior in the psychrophilic demosponge Amphilectus lobatus: stolonial movement. During stolonial movement, sponges produce outgrowths (stolons) that crawl along a substrate with a speed of 4.4 ± 2.2 μm min^-1 and branch, thus forming a complex net covering a considerable area of a substrate. This net is used by sponges to search for new points with appropriate environmental conditions for individual relocation. After such points are found, all cells of the parental sponge migrate through stolons, leaving a naked parental skeleton, forming one or several filial sponges in the new location. Thus, stolonial movement combines traits of crawling along the substrate and asexual reproduction. This behavior relies on massive cell dedifferentiation followed by coordinated cell migration to the point of new sponge body formation and their subsequent differentiation into specialized cell types.

Origin of animal multicellularity: precursors, causes, consequences-the choanoflagellate/sponge transition, neurogenesis and the Cambrian explosion

Evolving multicellularity is easy, especially in phototrophs and osmotrophs whose multicells feed like unicells. Evolving animals was much harder and unique; probably only one pathway via benthic ‘zoophytes’ with pelagic ciliated larvae allowed trophic continuity from phagocytic protozoa to gut-endowed animals. Choanoflagellate protozoa produced sponges. Converting sponge flask cells mediating larval settling to synaptically controlled nematocysts arguably made Cnidaria. I replace Haeckel's gastraea theory by a sponge/coelenterate/bilaterian pathway: Placozoa, hydrozoan diploblasty and ctenophores were secondary; stem anthozoan developmental mutations arguably independently generated coelomate bilateria and ctenophores. I emphasize animal origin's conceptual aspects (selective, developmental) related to feeding modes, cell structure, phylogeny of related protozoa, sequence evidence, ecology and palaeontology. Epithelia and connective tissue could evolve only by compensating for dramatically lower feeding efficiency that differentiation into non-choanocytes entails. Consequentially, larger bodies enabled filtering more water for bacterial food and harbouring photosynthetic bacteria, together adding more food than cell differentiation sacrificed. A hypothetical presponge of sessile triploblastic sheets (connective tissue sandwiched between two choanocyte epithelia) evolved oogamy through selection for larger dispersive ciliated larvae to accelerate benthic trophic competence and overgrowing protozoan competitors. Extinct Vendozoa might be elaborations of this organismal grade with choanocyte-bearing epithelia, before poriferan water channels and cnidarian gut/nematocysts/synapses evolved.

This article is part of the themed issue ‘Evo-devo in the genomics era, and the origins of morphological diversity’.

Think like a sponge: The genetic signal of sensory cells in sponges

A complex genetic repertoire underlies the apparently simple body plan of sponges. Among the genes present in poriferans are those fundamental to the sensory and nervous systems of other animals. Sponges are dynamic and sensitive animals and it is intuitive to link these genes to behaviour. The proposal that ctenophores are the earliest diverging metazoan has led to the question of whether sponges possess a 'pre-nervous' system or have undergone nervous system loss. Both lines of thought generally assume that the last common ancestor of sponges and eumetazoans possessed the genetic modules that underlie sensory abilities. By corollary extant sponges may possess a sensory cell homologous to one present in the last common ancestor, a hypothesis that has been studied by gene expression. We have performed a meta-analysis of all gene expression studies published to date to explore whether gene expression is indicative of a feature's sensory function. In sponges we find that eumetazoan sensory-neural markers are not particularly expressed in structures with known sensory functions. Instead it is common for these genes to be expressed in cells with no known or uncharacterized sensory function. Indeed, many sensory-neural markers so far studied are expressed during development, perhaps because many are transcription factors. This suggests that the genetic signal of a sponge sensory cell is dissimilar enough to be unrecognizable when compared to a bilaterian sensory or neural cell. It is possible that sensory-neural markers have as yet unknown functions in sponge cells, such as assembling an immunological synapse in the larval globular cell. Furthermore, the expression of sensory-neural markers in non-sensory cells, such as adult and larval epithelial cells, suggest that these cells may have uncharacterized sensory functions. While this does not rule out the co-option of ancestral sensory modules in later evolving groups, a distinct genetic foundation may underlie the sponge sensory system.

The animal sensorimotor organization: a challenge for the environmental complexity thesis

Godfrey-Smith's environmental complexity thesis (ECT) is most often applied to multicellular animals and the complexity of their macroscopic environments to explain how cognition evolved. We think that the ECT may be less suited to explain the origins of the animal bodily organization, including this organization's potentiality for dealing with complex macroscopic environments. We argue that acquiring the fundamental sensorimotor features of the animal body may be better explained as a consequence of dealing with internal bodily-rather than environmental complexity. To press and elucidate this option, we develop the notion of an animal sensorimotor organization (ASMO) that derives from an internal coordination account for the evolution of early nervous systems. The ASMO notion is a reply to the question how a collection of single cells can become integrated such that the resulting multicellular organization becomes sensitive to and can manipulate macroscopic features of both the animal body and its environment. In this account, epithelial contractile tissues play the central role in the organization behind complex animal bodies. In this paper, we relate the ASMO concept to recent work on epithelia, which provides empirical evidence that supports central assumptions behind the ASMO notion. Second, we discuss to what extent the notion applies to basic animal architectures, exemplified by sponges and jellyfish. We conclude that the features exhibited by the ASMO are plausibly explained by internal constraints acting on and within this multicellular organization, providing a challenge for the role the ECT plays in this context.

Using a thermistor flowmeter with attached video camera for monitoring sponge excurrent speed and oscular behaviour

A digital, four-channel thermistor flowmeter integrated with time-lapse cameras was developed as an experimental tool for measuring pumping rates in marine sponges, particularly those with small excurrent openings (oscula). Combining flowmeters with time-lapse imagery yielded valuable insights into the contractile behaviour of oscula in Cliona orientalis. Osculum cross-sectional area (OSA) was positively correlated to measured excurrent speeds (ES), indicating that sponge pumping and osculum contraction are coordinated behaviours. Both OSA and ES were positively correlated to pumping rate (Q). Diel trends in pumping activity and osculum contraction were also observed, with sponges increasing their pumping activity to peak at midday and decreasing pumping and contracting oscula at night. Short-term elevation of the suspended sediment concentration (SSC) within the seawater initially decreased pumping rates by up to 90%, ultimately resulting in closure of the oscula and cessation of pumping.

Physiology and Evolution of Voltage-Gated Calcium Channels in Early Diverging Animal Phyla: Cnidaria, Placozoa, Porifera and Ctenophora

Voltage-gated calcium (Ca_v) channels serve dual roles in the cell, where they can both depolarize the membrane potential for electrical excitability, and activate transient cytoplasmic Ca²⁺ signals. In animals, Ca_v channels play crucial roles including driving muscle contraction (excitation-contraction coupling), gene expression (excitation-transcription coupling), pre-synaptic and neuroendocrine exocytosis (excitation-secretion coupling), regulation of flagellar/ciliary beating, and regulation of cellular excitability, either directly or through modulation of other Ca²⁺-sensitive ion channels. In recent years, genome sequencing has provided significant insights into the molecular evolution of Ca_v channels. Furthermore, expanded gene datasets have permitted improved inference of the species phylogeny at the base of Metazoa, providing clearer insights into the evolution of complex animal traits which involve Ca_v channels, including the nervous system. For the various types of metazoan Ca_v channels, key properties that determine their cellular contribution include: Ion selectivity, pore gating, and, importantly, cytoplasmic protein-protein interactions that direct sub-cellular localization and functional complexing. It is unclear when these defining features, many of which are essential for nervous system function, evolved. In this review, we highlight some experimental observations that implicate Ca_v channels in the physiology and behavior of the most early-diverging animals from the phyla Cnidaria, Placozoa, Porifera, and Ctenophora. Given our limited understanding of the molecular biology of Ca_v channels in these basal animal lineages, we infer insights from better-studied vertebrate and invertebrate animals. We also highlight some apparently conserved cellular functions of Ca_v channels, which might have emerged very early on during metazoan evolution, or perhaps predated it.

Elements of a 'nervous system' in sponges

Genomic and transcriptomic analyses show that sponges possess a large repertoire of genes associated with neuronal processes in other animals, but what is the evidence these are used in a coordination or sensory context in sponges? The very different phylogenetic hypotheses under discussion today suggest very different scenarios for the evolution of tissues and coordination systems in early animals. The sponge genomic 'toolkit' either reflects a simple, pre-neural system used to protect the sponge filter or represents the remnants of a more complex signalling system and sponges have lost cell types, tissues and regionalization to suit their current suspension-feeding habit. Comparative transcriptome data can be informative but need to be assessed in the context of knowledge of sponge tissue structure and physiology. Here, I examine the elements of the sponge neural toolkit including sensory cells, conduction pathways, signalling molecules and the ionic basis of signalling. The elements described do not fit the scheme of a loss of sophistication, but seem rather to reflect an early specialization for suspension feeding, which fits with the presumed ecological framework in which the first animals evolved.

Predation and the origin of neurones

The core design of spiking neurones is remarkably similar throughout the animal kingdom. Their basic function as fast-signalling thresholding cells might have been established very early in their evolutionary history. Identifying the selection pressures that drove animals to evolve spiking neurones could help us interpret their design and function today. We review fossil, ecological and molecular evidence to investigate when and why animals evolved spiking neurones. Fossils suggest that animals evolved nervous systems soon after the advent of animal-on-animal predation, 550 million years ago (MYa). Between 550 and 525 MYa, we see the first fossil appearances of many animal innovations, including eyes. Animal behavioural complexity increased during this period as well, as evidenced by their traces, suggesting that nervous systems were an innovation of that time. Fossils further suggest that, before 550 MYa, animals were either filter feeders or microbial mat grazers. Extant sponges and Trichoplax perform these tasks using energetically cheaper alternatives than spiking neurones. Genetic evidence testifies that nervous systems evolved before the protostome-deuterostome split. It is less clear whether nervous systems evolved before the cnidarian-bilaterian split, so cnidarians and bilaterians might have evolved their nervous systems independently. The fossil record indicates that the advent of predation could fit into the window of time between those two splits, though molecular clock studies dispute this claim. Collectively, these lines of evidence indicate that animals evolved spiking neurones soon after they started eating each other. The first sensory neurones could have been threshold detectors that spiked in response to other animals in their proximity, alerting them to perform precisely timed actions, such as striking or fleeing.

A new flow-regulating cell type in the Demosponge Tethya wilhelma - functional cellular anatomy of a leuconoid canal system

Demosponges possess a leucon-type canal system which is characterized by a highly complex network of canal segments and choanocyte chambers. As sponges are sessile filter feeders, their aquiferous system plays an essential role in various fundamental physiological processes. Due to the morphological and architectural complexity of the canal system and the strong interdependence between flow conditions and anatomy, our understanding of fluid dynamics throughout leuconoid systems is patchy. This paper provides comprehensive morphometric data on the general architecture of the canal system, flow measurements and detailed cellular anatomical information to help fill in the gaps. We focus on the functional cellular anatomy of the aquiferous system and discuss all relevant cell types in the context of hydrodynamic and evolutionary constraints. Our analysis is based on the canal system of the tropical demosponge Tethya wilhelma, which we studied using scanning electron microscopy. We found a hitherto undescribed cell type, the reticuloapopylocyte, which is involved in flow regulation in the choanocyte chambers. It has a highly fenestrated, grid-like morphology and covers the apopylar opening. The minute opening of the reticuloapopylocyte occurs in an opened, intermediate and closed state. These states permit a gradual regulation of the total apopylar opening area. In this paper the three states are included in a theoretical study into flow conditions which aims to draw a link between functional cellular anatomy, the hydrodynamic situation and the regular body contractions seen in T. wilhelma. This provides a basis for new hypotheses regarding the function of bypass elements and the role of hydrostatic pressure in body contractions. Our study provides insights into the local and global flow conditions in the sponge canal system and thus enhances current understanding of related physiological processes.

The evolution and function of the Pax/Six regulatory network in sponges

Examining the origins of highly conserved gene regulatory networks (GRNs) will inform our understanding of the evolution of animal body plans. Sponges are believed to be the most ancient extant metazoan lineage, and as such, hold clues about the evolution of genetic programs deployed in animal development. We used the emerging freshwater sponge model, Ephydatia muelleri, to study the evolutionary origins of the Pax/Six/Eya/Dac (PSED) GRN. Orthologs to Pax and Six family members are present in E. muelleri and are expressed in endothelial cells lining the canal system as well as cells in the choanoderm. Knockdown of EmPaxB and EmSix1/2 by RNAi resulted in defects to the canal systems. We further show that PaxB may be in a regulatory relationship with Six1/2 in E. muelleri, thus demonstrating that a component of the PSED network was present early in metazoan evolution.

Ultrastructure of the ciliated cells of the free-swimming larva, and sessile stages, of the marine sponge Haliclona indistincta (Demospongiae: Haplosclerida)

We provide a detailed, comparative study of the ciliated cells of the marine haplosclerid sponge Haliclona indistincta, in order to make data available for future phylogenetic comparisons at the ultrastructural level. Our study focuses on the description and analysis of the larval epithelial cells, and choanocytes of the metamorphosed juvenile sponge. The ultrastructure of the two cell types is sufficiently different to prevent our ability to conclusively determine the origin of the choanocytes from the larval ciliated cells. However, ciliated, epithelial cells were observed in a migratory position within the inner cell mass of the larval stages. Some cilia were observed within the cell's cytoplasm, which is indicative of the ciliated epithelial cell undergoing transdifferentiation into a choanocyte; while traces of other ciliated epithelial cells were contained within phagosomes, suggesting they are phagocytosed. We compared our data with other species described in the literature. However, any phylogenetic inference must wait until further detailed comparisons can be made with species whose phylogenetic position has been determined by other means, such as phylogenomics, in order to more closely link genomic, and morphological information.

Phylogeny drives large scale patterns in Australian marine bioactivity and provides a new chemical ecology rationale for future biodiscovery

Twenty-five years of Australian marine bioresources collecting and research by the Australian Institute of Marine Science (AIMS) has explored the breadth of latitudinally and longitudinally diverse marine habitats that comprise Australia's ocean territory. The resulting AIMS Bioresources Library and associated relational database integrate biodiversity with bioactivity data, and these resources were mined to retrospectively assess biogeographic, taxonomic and phylogenetic patterns in cytotoxic, antimicrobial, and central nervous system (CNS)-protective bioactivity. While the bioassays used were originally chosen to be indicative of pharmaceutically relevant bioactivity, the results have qualified ecological relevance regarding secondary metabolism. In general, metazoan phyla along the deuterostome phylogenetic pathway (eg to Chordata) and their ancestors (eg Porifera and Cnidaria) had higher percentages of bioactive samples in the assays examined. While taxonomy at the phylum level and higher-order phylogeny groupings helped account for observed trends, taxonomy to genus did not resolve the trends any further. In addition, the results did not identify any biogeographic bioactivity hotspots that correlated with biodiversity hotspots. We conclude with a hypothesis that high-level phylogeny, and therefore the metabolic machinery available to an organism, is a major determinant of bioactivity, while habitat diversity and ecological circumstance are possible drivers in the activation of this machinery and bioactive secondary metabolism. This study supports the strategy of targeting phyla from the deuterostome lineage (including ancestral phyla) from biodiverse marine habitats and ecological niches, in future biodiscovery, at least that which is focused on vertebrate (including human) health.

The need for data standards in zoomorphology

eScience is a new approach to research that focuses on data mining and exploration rather than data generation or simulation. This new approach is arguably a driving force for scientific progress and requires data to be openly available, easily accessible via the Internet, and compatible with each other. eScience relies on modern standards for the reporting and documentation of data and metadata. Here, we suggest necessary components (i.e., content, concept, nomenclature, format) of such standards in the context of zoomorphology. We document the need for using data repositories to prevent data loss and how publication practice is currently changing, with the emergence of dynamic publications and the publication of digital datasets. Subsequently, we demonstrate that in zoomorphology the scientific record is still limited to published literature and that zoomorphological data are usually not accessible through data repositories. The underlying problem is that zoomorphology lacks the standards for data and metadata. As a consequence, zoomorphology cannot participate in eScience. We argue that the standardization of morphological data requires i) a standardized framework for terminologies for anatomy and ii) a formalized method of description that allows computer-parsable morphological data to be communicable, compatible, and comparable. The role of controlled vocabularies (e.g., ontologies) for developing respective terminologies and methods of description is discussed, especially in the context of data annotation and semantic enhancement of publications. Finally, we introduce the International Consortium for Zoomorphology Standards, a working group that is open to everyone and whose aim is to stimulate and synthesize dialog about standards. It is the Consortium's ultimate goal to assist the zoomorphology community in developing modern data and metadata standards, including anatomy ontologies, thereby facilitating the participation of zoomorphology in eScience.

Independent evolution of striated muscles in cnidarians and bilaterians

Striated muscles are present in bilaterian animals (for example, vertebrates, insects and annelids) and some non-bilaterian eumetazoans (that is, cnidarians and ctenophores). The considerable ultrastructural similarity of striated muscles between these animal groups is thought to reflect a common evolutionary origin. Here we show that a muscle protein core set, including a type II myosin heavy chain (MyHC) motor protein characteristic of striated muscles in vertebrates, was already present in unicellular organisms before the origin of multicellular animals. Furthermore, 'striated muscle' and 'non-muscle' myhc orthologues are expressed differentially in two sponges, compatible with a functional diversification before the origin of true muscles and the subsequent use of striated muscle MyHC in fast-contracting smooth and striated muscle. Cnidarians and ctenophores possess striated muscle myhc orthologues but lack crucial components of bilaterian striated muscles, such as genes that code for titin and the troponin complex, suggesting the convergent evolution of striated muscles. Consistently, jellyfish orthologues of a shared set of bilaterian Z-disc proteins are not associated with striated muscles, but are instead expressed elsewhere or ubiquitously. The independent evolution of eumetazoan striated muscles through the addition of new proteins to a pre-existing, ancestral contractile apparatus may serve as a model for the evolution of complex animal cell types.

The physiology and molecular biology of sponge tissues

Sponges have become the focus of studies on molecular evolution and the evolution of animal body plans due to their ancient branching point in the metazoan lineage. Whereas our former understanding of sponge function was largely based on a morphological perspective, the recent availability of the first full genome of a sponge (Amphimedon queenslandica), and of the transcriptomes of other sponges, provides a new way of understanding sponges by their molecular components. This wealth of genetic information not only confirms some long-held ideas about sponge form and function but also poses new puzzles. For example, the Amphimedon sponge genome tells us that sponges possess a repertoire of genes involved in control of cell proliferation and in regulation of development. In vitro expression studies with genes involved in stem cell maintenance confirm that archaeocytes are the main stem cell population and are able to differentiate into many cell types in the sponge including pinacocytes and choanocytes. Therefore, the diverse roles of archaeocytes imply differential gene expression within a single cell ontogenetically, and gene expression is likely also different in different species; but what triggers cells to enter one pathway and not another and how each archaeocyte cell type can be identified based on this gene knowledge are new challenges. Whereas molecular data provide a powerful new tool for interpreting sponge form and function, because sponges are suspension feeders, their body plan and physiology are very much dependent on their physical environment, and in particular on flow. Therefore, in order to integrate new knowledge of molecular data into a better understanding the sponge body plan, it is important to use an organismal approach. In this chapter, we give an account of sponge body organization as it relates to the physiology of the sponge in light of new molecular data. We focus, in particular, on the structure of sponge tissues and review descriptive as well as experimental work on choanocyte morphology and function. Special attention is given to pinacocyte epithelia, cell junctions, and the molecules present in sponge epithelia. Studies describing the role of the pinacoderm in sensing, coordination, and secretion are reviewed. A wealth of recent work describes gene presence and expression patterns in sponge tissues during development, and we review this in the context of the previous descriptions of sponge morphology and physiology. A final section addresses recent findings of genes involved in the immune response. This review is far from exhaustive but intends rather to revisit for non-specialists key aspects of sponge morphology and physiology in light of new molecular data as a means to better understand and interpret sponge form and function today.

RNA interference in marine and freshwater sponges: actin knockdown in Tethya wilhelma and Ephydatia muelleri by ingested dsRNA expressing bacteria

Background

The marine sponge Tethya wilhelma and the freshwater sponge Ephydatia muelleri are emerging model organisms to study evolution, gene regulation, development, and physiology in non-bilaterian animal systems. Thus far, functional methods (i.e., loss or gain of function) for these organisms have not been available.

Results

We show that soaking developing freshwater sponges in double-stranded RNA and/or feeding marine and freshwater sponges bacteria expressing double-stranded RNA can lead to RNA interference and reduction of targeted transcript levels. These methods, first utilized in C. elegans, have been adapted for the development and feeding style of easily cultured marine and freshwater poriferans. We demonstrate phenotypic changes result from 'knocking down' expression of the actin gene.

Conclusion

This technique provides an easy, efficient loss-of-function manipulation for developmental and gene regulatory studies in these important non-bilaterian animals.