Like a `rolling stone': quantitative analysis of the body movement and skeletal dynamics of the sponge Tethya wilhelma

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.

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.

In situ observation of sponge trails suggests common sponge locomotion in the deep central Arctic

In 2016, the research ice-breaker Polarstern surveyed the submerged peaks of the permanently ice-covered Langseth Ridge, a tectonic feature comprising the Karasik seamount and two deeper seamount peaks, abutting the Gakkel ultra-slow spreading ridge (87°N 62°E to 85.5°N 57.4°E)¹. A towed marine camera sled and a hybrid remotely operated vehicle revealed these peaks to be covered by a dense demosponge community, at first glance reminiscent of North Atlantic Geodia grounds (sensu²). Sponges were observed on top of a thick layer of spicule mat (Figure 1 and Video S1), intermixed with underlying layers of empty siboglinid tubes and bivalve shells, a substrate covering almost the entire seafloor. We observed trails of densely interwoven spicules connected directly to the underside or lower flanks of sponge individuals (Figure 1), suggesting these trails are traces of motile sponges. This is the first time abundant sponge trails have been observed in situ and attributed to sponge mobility. Given the low primary production in this permanently ice-covered region, these trails may relate to feeding behavior and/or a strategy for dispersal of juveniles. Such trails may remain visible for long periods given the regionally low sedimentation rates.

Developmental processes in Ediacara macrofossils

The Ediacara Biota preserves the oldest fossil evidence of abundant, complex metazoans. Despite their significance, assigning individual taxa to specific phylogenetic groups has proved problematic. To better understand these forms, we identify developmentally controlled characters in representative taxa from the Ediacaran White Sea assemblage and compare them with the regulatory tools underlying similar traits in modern organisms. This analysis demonstrates that the genetic pathways for multicellularity, axial polarity, musculature, and a nervous system were likely present in some of these early animals. Equally meaningful is the absence of evidence for major differentiation of macroscopic body units, including distinct organs, localized sensory machinery or appendages. Together these traits help to better constrain the phylogenetic position of several key Ediacara taxa and inform our views of early metazoan evolution. An apparent lack of heads with concentrated sensory machinery or ventral nerve cords in such taxa supports the hypothesis that these evolved independently in disparate bilaterian clades.

Planctopirus ephydatiae, a novel Planctomycete isolated from a freshwater sponge

The microbiome of freshwater sponges is rarely studied, and not a single novel bacterial species has been isolated and subsequently characterized from a freshwater sponge to date. A previous study showed that 14.4% of the microbiome from Ephydatia fluviatilis belong to the phylum Planctomycetes. Therefore, we sampled an Ephydatia sponge from a freshwater lake and employed enrichment techniques targeting bacteria from the phylum Planctomycetes. The obtained strain spb1^T was subject to genomic and phenomic characterization and found to represent a novel planctomycetal species proposed as Planctopirus ephydatiae sp. nov. (DSM 106606 = CECT 9866). In the process of differentiating spb1^T from its next relative Planctopirus limnophila DSM 3776^T, we identified and characterized the first phage - Planctopirus phage vB_PlimS_J1 - infecting planctomycetes that was only mentioned anecdotally before. Interestingly, classical chemotaxonomic methods would have failed to distinguish Planctopirus ephydatiae strain spb1^T from Planctopirus limnophila DSM 3776^T. Our findings demonstrate and underpin the need for whole genome-based taxonomy to detect and differentiate planctomycetal species.

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.

The ctenophore lineage is older than sponges? That cannot be right! Or can it?

Recent phylogenetic analyses resulting from collection of whole genome data suggest that ctenophores, or comb jellies, are sister to all other animals. Even before publication, this result prompted discussion among researchers. Here, I counter common criticisms raised about this result and show that assumptions placing sponges as the basal-most extant animal lineage are based on limited evidence and questionable premises. For example, the idea that sponges are simple and the reported similarity of sponge choanocytes to Choanflagellata do not provide useful characters for determining the positions of sponges within the animal tree. Intertwined with discussion of basal metazoan phylogeny is consideration of the evolution of neuronal systems. Recent data show that neural systems of ctenophores are vastly different from those of other animals and use different sets of cellular and genetic mechanisms. Thus, neural systems appear to have at least two independent origins regardless of whether ctenophores or sponges are the earliest branching extant animal lineage.

Origin of the neuro-sensory system: new and expected insights from sponges

The capacity of all cells to respond to stimuli implies the conduction of information at least over short distances. In multicellular organisms, more complex systems of integration and coordination of activities are necessary. In most animals, the processing of information is performed by a nervous system. Among the most basal taxa, sponges are nerveless so that it is traditionally assumed that the integrated neuro-sensory system originated only once in Eumetazoa, a hypothesis not in agreement with some recent phylogenomic studies. The aim of this review is to show that recent data on sponges might provide clues for understanding the origin of this complex system. First, sponges are able to react to external stimuli, and some of them display spontaneous movement activities. These coordinated behaviors involve nervous system-like mechanisms, such as action potentials and/or neurotransmitters. Second, genomic analyses show that sponges possess genes orthologous to those involved in the patterning or functioning of the neuro-sensory system in Eumetazoa. Finally, some of these genes are expressed in specific cells (flask cells, choanocytes). Together with ultrastructural data, this gives rise to challenging hypotheses concerning cell types that might play neuro-sensory-like roles in sponges.

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.

The GABAergic-like system in the marine demosponge Chondrilla nucula

Gamma-amino butyric acid (GABA) is believed to be the principal inhibitory neurotransmitter in the mammalian central nervous system, a function that has been extended to a number of invertebrate systems. The presence of GABA in the marine demosponge Chondrilla nucula was verified using immunofluorescence detection and high-pressure liquid chromatography. A strong GABA-like immunoreactivity (IR) was found associated with choanocytes, exopinacocytes, endopinacocytes lining inhalant, and exhalant canals, as well as in archaeocytes scattered in the mesohyl. The capacity to synthesize GABA from glutamate and to transport it into the vesicles was confirmed by the presence in C. nucula of glutamate decarboxylase (GAD) and vesicular GABA transporters (vGATs), respectively. GAD-like and vGAT-like IR show the same distribution as GABA-like IR. Supporting the similarity between sponge and mammalian proteins, bands with an apparent molecular weight of about 65-67 kDa and 57 kDa were detected using antibodies raised against mammalian GAD and vGAT, respectively. A functional metabotropic GABA(B)-like receptor is also present in C. nucula. Indeed, both GABA(B) R1 and R2 isoforms were detected by immunoblot and immunofluorescence. Also in this case, IR was found in choanocytes, exopinacocytes, and endopinacocytes. The content of GABA in C. nucula amounts to 1225.75 +/- 79 pmol/mg proteins and GABA is released into the medium when sponge cells are depolarized. In conclusion, this study is the first indication of the existence of the GABA biosynthetic enzyme GAD and of the GABA transporter vGAT in sponges, as well as the first demonstration that the neurotransmitter GABA is released extracellularly.

GABA and glutamate specifically induce contractions in the sponge Tethya wilhelma

Sponges (Porifera) are nerve- and muscleless. Nevertheless, they react to external stimuli in a coordinated way, by body contraction, oscule closure or stopping pumping activity. The underlying mechanisms are still unknown, but evidence has been found for chemical messenger-based systems. We used the sponge Tethya wilhelma to test the effect of gamma-aminobutyric acid (GABA) and glutamate (L: -Glu) on its contraction behaviour. Minimal activating concentrations were found to be 0.5 microM (GABA) and 50 microM (L: -Glu), respectively. Taking maximum relative contraction speed and minimal relative projected body area as a measure of the sponge's response, a comparison of the dose-response curves indicated a higher sensitivity of the contractile tissue for GABA than for L: -Glu. The concentrations eliciting the same contractile response differ by about 100-fold more than the entire concentration range tested. In addition, desensitising effects and spasm-like reactions were observed. Presumably, a GABA/L: -Glu metabotropic receptor-based system is involved in the regulation of contraction in T. wilhelma. We discuss a coordination system for sponges based on hypothetical chemical messenger pathways.