Differential Gene Expression Between Polymorphic Zooids of the Marine Bryozoan Bugulina stolonifera

The genome sequence of an erect bryozoan, Bugulina stolonifera (Ryland, 1960)

We present a genome assembly from a Bugulina stolonifera colony (an erect bryozoan; Bryozoa; Gymnolaemata; Cheilostomatida; Bugulidae). The genome sequence is 235 megabases in span. Most of the assembly (99.85%) is scaffolded into 11 chromosomal pseudomolecules. The mitochondrial genome was also assembled and is 14.4 kilobases long.

Phylogenomics reveals deep relationships and diversification within phylactolaemate bryozoans

Bryozoans are mostly sessile colonial invertebrates that inhabit all kinds of aquatic ecosystems. Extant bryozoan species fall into two clades with one of them, Phylactolaemata, being the only exclusively freshwater clade. Phylogenetic relationships within the class Phylactolaemata have long been controversial owing to their limited distinguishable characteristics that reflect evolutionary relationships. Here, we present the first phylogenomic analysis of Phylactolaemata using transcriptomic data combined with dense taxon sampling of six families to better resolve the interrelationships and to estimate divergence time. Using maximum-likelihood and Bayesian inference approaches, we recovered a robust phylogeny for Phylactolaemata in which the interfamilial relationships are fully resolved. We show Stephanellidae is the sister taxon of all other phylactolaemates and confirm that Lophopodidae represents the second offshoot within the phylactolaemate tree. Plumatella fruticosa clearly falls outside Plumatellidae as previous investigations have suggested, and instead clusters with Pectinatellidae and Cristatellidae as the sister taxon of Fredericellidae. Our results demonstrate that cryptic speciation is very likely in F. sultana and in two species of Plumatella (P. repens and P. casmiana). Divergence time estimates show that Phylactolaemata appeared at the end of the Ediacaran and started to diverge in the Silurian, although confidence intervals were large for most nodes. The radiation of most extant phylactolaemate families occurred mainly in the Palaeogene and Neogene highlighting post-extinction diversification.

Small, but smart: Fine structure of an avicularium in Dendrobeania fruticosa (Bryozoa: Cheilostomata)

Bryozoans are small benthic suspension-feeding colonial animals. Among this phylum, there are representatives showing a lesser or greater degree of polymorphism, and the most common type of polymorphic zooids is the avicularium. Here we present a detailed description of the bird's-head shaped avicularium in Dendrobeania fruticosa. The body cavity of the avicularium demonstrates an acoelomate condition: along the cystid walls, there is neither the layer of extracellular matrix toward the epidermis, nor coelomic lining. However, a layer of extracellular matrix and epithelialized cells lie under the epidermis of the tentacle sheath. Probably, such construction helps the tentacle sheath to acquire some rigidity-it is the only region of the body wall without an ectocyst. We did not find typical funicular strands in the avicularium, but there is a delicate mesh composed of stellate cells with thin and long projections, which sometimes isolate the spaces filled with a heterogeneous matrix. The proximal ends of the adductors, abductors, and polypide retractors are attached to the body wall via typical epidermal tendon cells, which possess numerous bundles of tonofilaments. The distal ends of the abductors and adductors attach to the frontal membrane or upper vestibular membrane, respectively. The inner organic layer of the ectocyst in these regions forms large protrusions, from which numerous thin outgrowths branch off. We suggest them to be a functional analogue of apodemes and apodemal filaments in arthropods. "Apodemal" tendon cells have long and thin projections that line the outgrowths of the ectocyst and surround the distal ends of the muscle cells. At these sites, "apodemal" tendon cells possess numerous tonofilaments. The vestigial polypide includes the tentacle sheath, rudimentary lophophore, cerebral ganglion, and polypide retractors. The sensory part of 5HT-positive cells of the frontal membrane is dendrite-shaped and embedded in the inner organic layer of the ectocyst.

Conservative and Atypical Ferritins of Sponges

Ferritins comprise a conservative family of proteins found in all species and play an essential role in resistance to redox stress, immune response, and cell differentiation. Sponges (Porifera) are the oldest Metazoa that show unique plasticity and regenerative potential. Here, we characterize the ferritins of two cold-water sponges using proteomics, spectral microscopy, and bioinformatic analysis. The recently duplicated conservative HdF1a/b and atypical HdF2 genes were found in the Halisarca dujardini genome. Multiple related transcripts of HpF1 were identified in the Halichondria panicea transcriptome. Expression of HdF1a/b was much higher than that of HdF2 in all annual seasons and regulated differently during the sponge dissociation/reaggregation. The presence of the MRE and HRE motifs in the HdF1 and HdF2 promotor regions and the IRE motif in mRNAs of HdF1 and HpF indicates that sponge ferritins expression depends on the cellular iron and oxygen levels. The gel electrophoresis combined with specific staining and mass spectrometry confirmed the presence of ferric ions and ferritins in multi-subunit complexes. The 3D modeling predicts the iron-binding capacity of HdF1 and HpF1 at the ferroxidase center and the absence of iron-binding in atypical HdF2. Interestingly, atypical ferritins lacking iron-binding capacity were found in genomes of many invertebrate species. Their function deserves further research.