Calcium localization in the shell-forming tissue of the freshwater snail, Biomphalaria glabrata: a comparative study of various methods for localizing calcium

Evolution and diversity of alpha-carbonic anhydrases in the mantle of the Mediterranean mussel (Mytilus galloprovincialis)

The α-carbonic anhydrases (α-CAs) are a large and ancient group of metazoan-specific enzymes. They generate bicarbonate from metabolic carbon dioxide and through calcium carbonate crystal formation play a key role in the regulation of mineralized structures. To better understand how α-CAs contribute to shell mineralization in the marine Mediterranean mussel (Mytilus galloprovincialis) we characterized them in the mantle. Phylogenetic analysis revealed that mollusc α-CA evolution was affected by lineage and species-specific events. Ten α-CAs were found in the Mediterranean mussel mantle and the most abundant form was named, MgNACR, as it grouped with oyster nacreins (NACR). Exposure of the Mediterranean mussel to reduced water salinity (18 vs 37 ppt), caused a significant reduction (p < 0.05) in mantle esterase activity and MgNACR transcript abundance (p < 0.05). Protonograms revealed multiple proteins in the mantle with α-CA hydratase activity and mapped to a protein with a similar size to that deduced for monomeric MgNACR. Our data indicate that MgNACR is a major α-CA enzyme in mantle and that by homology with oyster nacreins likely regulates mussel shell production. We propose that species-dependent α-CA evolution may contribute to explain the diversity of bivalve shell structures and their vulnerability to environmental changes.

Changes in energetic metabolism of Biomphalaria glabrata (Mollusca, Planorbidae) in response to exogenous calcium

Abstract Calcium is considered an essential element for the metabolism of aquatic snail Biomphalaria glabrata (Say, 1818), intermediate host of Schistosoma mansoni Sambon, 1907 in Brazil, and represents a limiting factor to its distribution and adaptation to the environment. This study investigated the effect of different concentrations of exogenous CaCO3 on the energetic metabolism of B. glabrata for better understanding the physiological interference of chemical elements dissolved in the environment with the physiology of this species. Sixty-day-old snails were distributed into six groups, five exposed to different concentrations of CaCO3 (20, 40, 60, 80 and 100 mg/L) and a control group. The exposure to CaCO3 was assessed over time, with analysis of 15 snails of each group in the following intervals: 1, 14, 21 or 30 days for hemolymph extraction. Concentrations of calcium and glucose in the hemolymph were determined by commercial kits, and organic acids were extracted using an ion exchange column and analyzed by high-performance liquid chromatography. Concentration of calcium in the hemolymph showed no significant difference (p>0.05) from the control group and between the concentrations tested. Concentration of glucose decreased (p<0.05) in the treatments of exposure to 20 and 40 mg/L and increased when exposed to 80 and 100 mg/L CaCO3 compared to control and to other concentrations tested over 30 days. The organic acids pyruvate, oxaloacetate, citrate, succinate, fumarate, beta-hydroxybutyrate and lactate presented increased concentrations, while propionate and acetoacetate, decreased concentrations, when exposed to CaCO3 compared to control. Considering the influence of different periods of exposure to CaCO3, on the 14th day, there were stronger alterations in the metabolism of B. glabrata. In conclusion, exposure to CaCO3 reduced the concentration of glucose, which is metabolized into pyruvate, the final product of glycolysis, and also influenced the energetic metabolism pathways, indicating an aerobic or partially anaerobic functioning.

The Carbonic Anhydrase Domain Protein Nacrein is Expressed in the Epithelial Cells of the Mantle and Acts as a Negative Regulator in Calcification in the Mollusc Pinctada fucata

Signals and organic matrix proteins secreted from the mantle are critical for the development of shells in molluscs. Nacrein, which is composed of a carbonic anhydrase domain and a Gly-X-Asn repeat domain, is one of the organic matrix proteins that accumulates in shells. In situ hybridization revealed that nacrein was expressed in the outer epithelial cells of the mantle of the pearl oyster Pinctada fucata. The recombinant nacrein protein inhibited the precipitation of calcium carbonate from a saturated solution containing CaCl2 and NaHCO3, indicating that it can act as a negative regulator for calcification in the shells of molluscs. Because deletion of the Gly-X-Asn repeat domain of nacrein had a significant effect on the ability of nacrein to inhibit the precipitation of calcium carbonate, it is conceivable that the repeat domain has a primary role in the inhibitory function of nacrein in shell formation. Together these studies suggest that nacrein functions as a negative regulator in calcification in the extrapallial space between the shell and the mantle by inhibiting the precipitation of CaCO3.

The major soluble 19.6 kDa protein of the organic shell matrix of the freshwater snail Biomphalaria glabrata is an N-glycosylated dermatopontin

The major Biomphalaria glabrata shell matrix protein of 19.6 kDa was isolated by preparative electrophoresis and sequenced. The sequence of 148 amino acids showed 32% sequence identity to mammalian dermatopontin sequences and 34-37% identity to two invertebrate dermatopontins described previously. A unique feature of the shell matrix dermatopontin was the presence of a single N-glycosylation consensus sequence, the asparagine of which was completely modified with a pentasaccharide. Sequence analysis of this short N-glycan by mass spectrometry and carbohydrate composition analysis indicated that it was the ubiquitous N-glycan core oligosaccharide with the exception that the terminal mannoses were 3-O-methylated. Dermatopontin is widespread in mammalian extracellular matrices, including the matrix of biominerals such as bone and teeth. Its occurrence in an invertebrate biomineral indicates that such phylogenetically distant biomineral-forming systems as vertebrate bone and mollusk shell share components which have undergone surprisingly few changes during a long evolution.

Seasonal- and age-dependent changes of the structure and chemical composition of the spherites in the midgut gland of the harvestmen Gyas annulatus (Opiliones)

Spherites--round laminated membrane bound structures--are located in the cytoplasm of all cell types of the midgut gland in the harvestmen Gyas annulatus. The spherites consist of an organic matrix composed of glycoproteins and proteoglycans whose sugar portion are carboxylated glycosaminoglycans. Different elements are embedded in this matrix, and their presence varies during the life cycle. All spherites in juveniles are composed of alternating concentrically arranged electron dense and electron lucent layers of organic matrix material before overwintering (December). At that time, spherites contain calcium, phosphorus and silicon. Calcium and phosphorus are located in their electron dense layers, and silicon spotwise, mainly peripheral. Material seems to be lost during overwintering of Gyas as electron lucent "empty" layers appear in spherites in March. The "lost" material could be used as energy supply and/or to provide molecules for synthesis processes during non-nourishing overwintering. Spherites do not contain calcium and phosphorus in July and October. These elements seem to have important biological relevance in the formation and hardening of the cuticle during the moultings in spring. In contrast to calcium and phosphorus, silicon is still stored in spherites in July and October but in decreasing concentration, therefore it could be involved in metabolic processes in adult Gyas. In the period from July to the end of their adult life in late autumn, an increasing number of spherites disintegrate and their remnant organic matrix material progressively aggregates with other cellular waste material in one or more huge vacuoles of glandular cells.

Calcium carbonate modifications in the mineralized shell of the freshwater snail Biomphalaria glabrata

The mineralized shell (consisting of calcium carbonate) of the tropical freshwater snail Biomphalaria glabrata was investigated with high resolution synchrotron X-ray powder diffractometry and X-ray absorption spectroscopy (EXAFS). Parts from different locations of the snail shell were taken from animals of different age grown under various keeping conditions. Additionally, eggs with ages of 60, 72, 120, and 140 hours were examined. Traces of aragonite were found as first crystalline phase in 120 h old eggs, however, Ca K-edge EXAFS indicated the presence of aragonitic structures already in the X-ray amorphous sample of 72 h age. The main component of the shell of adult animals was aragonite in all cases, but in some cases minor amounts of vaterite (below 1.5%) are formed. The content of vaterite is generally low in the oldest part of the shell (the center) and increases towards the mineralizing zone (the shell margin). In juvenile snails, almost no vaterite was detectable in any part of the shell.

Cytochemical localization of calcium in prefusion myoblasts from the chick embryo myotome

Myoblast fusion is a Ca2+-dependent process. The aim of this report was to study the localization of Ca2+ in prefusion myoblasts from the brachial somites of chick embryos (51-108 h of incubation), using the potassium pyroantimonate cytochemical method. When observed under a transmission electron microscope, electron-dense precipitates of Ca2+-antimonate were found in the basement membrane of the myotome, which separates the myotome from the adjacent mesenchyma. Within myoblasts, triads and sarcoplasmic reticulum associated with the first newly formed sarcomeres were observed, but a T-tubule network was not found. Moreover, Ca2+-antimonate precipitates were not observed in structures resembling T-tubules or sarcoplasmic reticulum. The results suggest that sarcomerogenesis and sarcoplasmic reticulum development occur simultaneously and that prefusion myoblasts have neither a T-tubule network nor Ca2+ deposits on sarcoplasmic reticulum. Small Ca2+ pools were found in the myoblast nuclei, cytoplasmic vesicles and mitochondrias. Ca2+-antimonate precipitates periodically distributed at the cell periphery, close to the cell membrane, were observed. These precipitates could represent internal Ca2+ stores located in the peripheral couplings and it is proposed that these pools of Ca2+ could be mobilized before fusion, leading to the increase in free intracellular Ca2+ that precedes myoblast fusion.