The effect of exuviae ingestion on lysosomal calcium accumulation and the presence of exosomes in the hepatopancreas of Porcellio scaber

The epidermis cells of mandible teeth in the terrestrial isopod Porcellio scaber: Differentiations for mineralisation with calcium phosphate and carbonate

Generally, the mineralisation of the crustacean cuticle occurs when the cuticle has expanded after moulting. However, in the partes incisivae of Porcellio scaber, cuticle mineralisation with calcium phosphate already occurs before the moult. We investigated the ultrastructure and distribution of organelles within the epidermis cells and searched for calcium-containing organelles using EDX and EFTEM analysis. We found two different cell types. Calcium carbonate-secreting C-cells, which resemble the epithelial cells of the general integument, and the P-cells, which, as an unusual feature, have cell extensions up to 400 μm long. During secretion of the partes incisivae, these extensions end at the unmineralised tip and the phosphate-containing middle region. Their cell bodies contain most of the mitochondria located in basal folds and a high amount of endoplasmic reticulum. The cell extensions contain many microtubules, endoplasmic reticulum, large and small vesicles and densely stained rod-shaped cisternae. The rod-shaped cisternae and the endoplasmic reticulum contain calcium. During cuticle mineralisation, vesicles, which probably belong to the endo-lysosomal system, contain calcium and phosphorus. They occur at some distance and close to the cuticle. The mineral in these vesicles has a similar composition to that within the cuticle, suggesting that they play a role in cuticle mineralisation.

Zika virus replication in glioblastoma cells: electron microscopic tomography shows 3D arrangement of endoplasmic reticulum, replication organelles, and viral ribonucleoproteins

Structural changes of two patient-derived glioblastoma cell lines after Zika virus infection were investigated using scanning transmission electron tomography on high-pressure-frozen, freeze-substituted samples. In Zika-virus-infected cells, Golgi structures were barely visible under an electron microscope, and viral factories appeared. The cytosol outside of the viral factories resembled the cytosol of uninfected cells. The viral factories contained largely deranged endoplasmic reticulum (ER), filled with many so-called replication organelles consisting of a luminal vesicle surrounded by the ER membrane. Viral capsids were observed in the vicinity of the replication organelles (cell line #12537 GB) or in ER cisternae at large distance from the replication organelles (cell line #15747 GB). Near the replication organelles, we observed many about 100-nm-long filaments that may represent viral ribonucleoprotein complexes (RNPs), which consist of the RNA genome and N protein oligomers. In addition, we compared Zika-virus-infected cells with cells infected with a phlebovirus (sandfly fever Turkey virus). Zika virions are formed in the ER, whereas phlebovirus virions are assembled in the Golgi apparatus. Our findings will help to understand the replication cycle in the virus factories and the building of the replication organelles in glioblastoma cells.

Extracellular vesicles and post-translational protein deimination signatures in haemolymph of the American lobster (Homarus americanus)

The American lobster (Homarus americanus) is a commercially important crustacean with an unusual long life span up to 100 years and a comparative animal model of longevity. Therefore, research into its immune system and physiology is of considerable importance both for industry and comparative immunology studies. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family that catalyses post-translational protein deimination via the conversion of arginine to citrulline. This can lead to structural and functional protein changes, sometimes contributing to protein moonlighting, in health and disease. PADs also regulate the cellular release of extracellular vesicles (EVs), which is an important part of cellular communication, both in normal physiology and in immune responses. Hitherto, studies on EVs in Crustacea are limited and neither PADs nor associated protein deimination have been studied in a Crustacean species. The current study assessed EV and deimination signatures in haemolymph of the American lobster. Lobster EVs were found to be a poly-dispersed population in the 10-500 nm size range, with the majority of smaller EVs, which fell within 22-115 nm. In lobster haemolymph, 9 key immune and metabolic proteins were identified to be post-translationally deiminated, while further 41 deiminated protein hits were identified when searching against a Crustacean database. KEGG (Kyoto encyclopedia of genes and genomes) and GO (gene ontology) enrichment analysis of these deiminated proteins revealed KEGG and GO pathways relating to a number of immune, including anti-pathogenic (viral, bacterial, fungal) and host-pathogen interactions, as well as metabolic pathways, regulation of vesicle and exosome release, mitochondrial function, ATP generation, gene regulation, telomerase homeostasis and developmental processes. The characterisation of EVs, and post-translational deimination signatures, reported in lobster in the current study, and the first time in Crustacea, provides insights into protein moonlighting functions of both species-specific and phylogenetically conserved proteins and EV-mediated communication in this long-lived crustacean. The current study furthermore lays foundation for novel biomarker discovery for lobster aquaculture.

Intracellular calcium phosphate deposits contribute to transcellular calcium transport within the hepatopancreas of Porcellio scaber

Like in most Crustacea, the cuticle of terrestrial isopods is hardened by a calcareous mineral phase. This rigid cuticle is frequently shed during a process called moulting. To reduce calcium loss, Porcellio scaber eats the shed cuticle, the exuviae, and absorb the calcium from it through large tubular diverticula of the intestine, called the mid gut glands or hepatopancreas. After moulting the absorbed calcium should be transported immediately into the hemolymph from which it is used to rapidly mineralize the new cuticle. This suggests that the hepatopancreas epithelium transports calcium from the lumen to the hemolymph. We used TEM, energy-filtered TEM and electron-probe X-ray microanalysis to analyse the distribution of elevated calcium within the hepatopancreas cells of P. scaber. We used animals in the postmoult stage that have eaten their exuviae and, as a control, those that have not ingested the exuviae. To minimize calcium loss within the samples, we used high pressure frozen and freeze substituted samples and propane-1-3-diol as floatation medium for thin-sectioning. The results reveal intracellular dense deposits containing calcium, phosphorus and oxygen at the apical microvillus membrane, within the cytoplasm, attached to vesicles and to the basolateral membrane, as well as extracellular between cells and the basal lamina. Control animals were devoid of these deposits. The results indicate that calcium from the exuviae is absorbed and transported across the epithelium into the hemolymph. We propose that during transport, intracellular calcium is bound to phosphate avoiding toxic effects of high concentrations of ionized calcium.