Three in one: evolution of viviparity, coenocytic placenta and polyembryony in cyclostome bryozoans

Background Placentation has evolved multiple times among both chordates and invertebrates. Although they are structurally less complex, invertebrate placentae are much more diverse in their origin, development and position. Aquatic colonial suspension-feeders from the phylum Bryozoa acquired placental analogues multiple times, representing an outstanding example of their structural diversity and evolution. Among them, the clade Cyclostomata is the only one in which placentation is associated with viviparity and polyembryony—a unique combination not present in any other invertebrate group. Results The histological and ultrastructural study of the sexual polymorphic zooids (gonozooids) in two cyclostome species, Crisia eburnea and Crisiella producta, revealed embryos embedded in a placental analogue (nutritive tissue) with a unique structure—comprising coenocytes and solitary cells—previously unknown in animals. Coenocytes originate via nuclear multiplication and cytoplasmic growth among the cells surrounding the early embryo. This process also affects cells of the membranous sac, which initially serves as a hydrostatic system but later becomes main part of the placenta. The nutritive tissue is both highly dynamic, permanently rearranging its structure, and highly integrated with its coenocytic ‘elements’ being interconnected via cytoplasmic bridges and various cell contacts. This tissue shows evidence of both nutrient synthesis and transport (bidirectional transcytosis), supporting the enclosed multiple progeny. Growing primary embryo produces secondary embryos (via fission) that develop into larvae; both the secondary embyos and larvae show signs of endocytosis. Interzooidal communication pores are occupied by 1‒2 specialized pore-cells probably involved in the transport of nutrients between zooids. Conclusions Cyclostome nutritive tissue is currently the only known example of a coenocytic placental analogue, although syncytial ‘elements’ could potentially be formed in them too. Structurally and functionally (but not developmentally) the nutritive tissue can be compared with the syncytial placental analogues of certain invertebrates and chordates. Evolution of the cyclostome placenta, involving transformation of the hydrostatic apparatus (membranous sac) and change of its function to embryonic nourishment, is an example of exaptation that is rather widespread among matrotrophic bryozoans. We speculate that the acquisition of a highly advanced placenta providing massive nourishment might support the evolution of polyembryony in cyclostomes. In turn, massive and continuous embryonic production led to the evolution of enlarged incubating polymorphic gonozooids hosting multiple progeny.

Properties Anisotropy of Additive Manufactured High-Porous Titanium Alloy with Non-Equiaxial Cellular Structure

Numeric simulation of compression test was carried out for a high-porous structure of a titanium alloy produced by additive manufacturing method with non-equiaxial performance of pore cells. The stress-strain state of a cellular titanium alloy with diamond-shaped unit cells was determined by the finite element method (FEM) in ABAQUS software for the plane formulation of the problem. The distribution of stresses, as well as the modulus of elasticity of the cellular material, was proved to depend on the loading direction.

Copper in Helix pomatia (Gastropoda) is regulated by one single cell type: differently responsive metal pools in rhogocytes

Like all other animal species, terrestrial pulmonate snails require Cu as an essential trace element. On the other hand, elevated amounts of Cu can exert toxic effects on snails. The homeostatic regulation of Cu must therefore be a pivotal goal of terrestrial pulmonates to survive. Upon administration of Cu, snails accumulate the metal nearly equally in most of their organs. Quantitative studies in connection with HPLC and electrospray ionization mass spectrometry reveal that a certain fraction of Cu in snails is bound to a Cu-metallothionein (Cu-MT) isoform that occurs in most organs at constant concentrations, irrespective of whether the animals had been exposed to physiological or elevated amounts of Cu. In situ hybridization demonstrates that at the cellular level, the Cu-binding MT isoform is exclusively expressed in the so-called pore cells (or rhogocytes), which can be found in all major snail organs. The number of pore cells with Cu-MT mRNA reaction products remains unaffected by Cu exposure. Rhogocytes also are major storage sites of Cu in a granular form, the metal quickly entering the snail tissues upon elevated exposure. The number of rhogocytes with granular Cu precipitations strongly increases upon Cu administration via food. Thus, whereas Cu-MT in the rhogocytes represents a stable pool of Cu that apparently serves physiological tasks, the granular Cu precipitations form a second, quickly inducible, and more easily available pool of the metal that serves Cu regulation by responding to superphysiological metal exposure.

Predominant role of the chorda tympani nerve in the maintenance of the taste pores: the influence of gustatory denervation in ear surgery

The effect on the taste pores of denervation of the chorda tympani nerve in the middle-ear cavity was studied comparing confocal laser microscopy with lingual nerve resection. Taste pore cells were stained for actin with rhodamine-phalloidin and positive fluorescence was observed as a ring shape at the transverse cross sections. Within three days after chorda tympani nerve resection the ring reaction disappeared, although the pore morphology remained intact as seen by scanning electron microscopy. On the other hand, lingual nerve resection did not induce such rapid disappearance of the ring reaction. These results suggest that the chorda tympani nerve plays a predominant role in the maintenance of actin filaments in taste pore cells.

The cytology of heavy metal accumulations in the digestive glands of three marine gastropods

In the digestive glands of gastropod molluscs, metals are metabolized in the sense that they are subject to inorganic biochemical processes within the epithelial cells and lumen of the digestive tubules and the pore cells in the intervening connective tissue. These systems have been examined in the tower shell Cerithium vulgatum Bruguieres, a sediment feeder, the top shell Monodonta articulata Lam., a grazing herbivore, and in the whelk Murex trunculus L., a carnivore whose prey includes Cerithium . These animals were taken from a Mediterranean environment polluted by heavy metals. In all three species the metals are compartmentalized within mineralized granules as phosphates and within lysosomal residual bodies in association with sulphur. However, the extent to which a particular metal is accumulated and the relative proportions that are bound within the different compartments are factors that are primarily determined by the species and not the concentration available in the environment. Thus Cerithium accumulates high concentrations of a wide range of metals from the ingested sediment and these are rendered insoluble and non-toxic in the digestive gland. This unavailability is transferred to Murex when it eats Cerithium because Murex does not accumulate the full range of metals from its prey. Indeed, for some metals there appears to be bioreduction rather than bioamplification. The grazing herbivore Monodonta articulata accumulates a third distinct spectrum of metals. The accumulations in each species do not reflect the levels of all the metals in the environment. The presence of metals in the digestive glands is associated with the removal of magnesium from the phosphate granules but also with an increase in the concentration of magnesium in the tissue. It is proposed that metals induce the formation of magnesium phosphate as a source of metal-binding phosphate ions.

Rôle des cellules S de l'épithélium caecal des Crustacés Isopodes dans la capture et la dégradation de protéines hémolymphatiques, et dans le stockage de catabolites (acide urique, sulfure de cuivre, phosphates)

The S cells within the tubules of the hepatopancreas in the terrestrial isopod Oniscus asellus show numerous infoldings of the plasma membrane, which are involved in the uptake of hemolymph proteins, and a lysosomal apparatus that ensures the breakdown of the ingested material. The catabolic process leads to an accumulation of wastes in the form of spherocrystals. The most important components of the spherocrystals are uric acid, copper sulfide, which we consider to originate in the breakdown of hemocyanin monomers, alkaline-earth phosphates, which could be produced by enzymatic activities, and zinc. Moreover, in the marine species Ligia oceanica a silver salt (sulfide?) is stored in the spherocrystals. The S cells function as a storage type of excretory system. Their role is similar to urate cells in arthropods, nephrocytes in insects, and pore cells in molluscs. In the latter, the storage of silver is important in marine environments only.

Ferritin as an exogenously derived yolk protein in Helisoma duryi (Mollusca: Pulmonata)

The iron storage protein ferritin is identified as a yolk component in Helisoma duryi by histochemistry, electron microscopy, energy dispersive analytical x-ray analysis, and radioimmunoassay. It was found to accumulate in the yolk granules of maturing oocytes when they attained a diameter of 50 μm. Extraction of the protein and its estimation by radioimmunoassay in tissues from reproducing and reproductively inactive (virgin) snails suggest that ferritin is synthesized extragonadally and transported in the blood to maturing oocytes in the ovotestis. Ferritin was also found in the digestive gland and in the mantle, which contains pore cells. Mantle ferritin levels fluctuated with reproductive activity. The possibility that pore cells play a role in regulating vitellogenic ferritin is discussed.