The aim of our work was to assess whether the cellular processes in the nephrocytes of the long-lived mussel Crenomytilus grayanus tend to acclimation or destruction under trace metal contamination. ...Mussels were collected from three sites in the north-western Pacific Ocean: reference site, upwelling site, and a site highly contaminated with trace metals. Concentration, subcellular distribution of trace metals (Cd, Cu, Zn, and Pb) in the mussel kidneys, and ultrastructural alterations of the nephrocytes were studied. To assess the total load of accumulated trace metals, the total concentration coefficient (∑СС) was determined.
In the kidneys of the reference C. grayanus, trace metals were eliminated from cell metabolism mainly by lysosomal granules or residue bodies. Under high levels of contamination, the defense mechanisms of C. grayanus are practically suppressed (no metallothionein-like protein peak, decreased content of granules) by the total effect of accumulated pollutants that leads to the destruction of cellular structures. Under natural conditions (upwelling site), increased accumulation of trace metals in the mussel kidneys did not lead to an increase in the number or size of lysosomal granules. However, abnormal high Cd accumulation in the kidneys caused the synthesis of high levels of metallothionein-like proteins that sequester most of the studied trace metals. To quickly lower the metal levels in nephrocytes under these conditions, a unique long-term acclimatory response — apocrine-like secretion in nephrocytes, which provides rapid elimination of me—MTLP complexes from the cell arose. Thus, our integrated study of the subcellular distribution of trace metals and ultrastructural alterations in nephrocytes allowed us to characterize the features of the structural and functional alterations in mussel cells under the field conditions tested.
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•Different approaches were integrated for comprehensive assessment.•Marine mussels from upwelling zone and contaminated site were studied.•Under high contamination, acclimation capability of mussels was overwhelmed•The unique acclimatory mechanism was observed in the nephrocytes of mussel from upwelling zone
This work presents the AYT2 line list: a comprehensive list of 115 million 1H2
32S vibration–rotation transitions computed using an empirically adjusted potential energy surface and an ab initio ...dipole moment surface. The line list gives complete coverage up to 11 000 cm−1 (wavelengths longer than 0.91 μm) for temperatures up to 2000 K. Room temperature spectra can be simulated up to 20 000 cm−1 (0.5 μm) but the predictions at visible wavelengths are less reliable. AYT2 is made available in electronic form as supplementary data to this paper at www.exomol.com.
The ultrastructure of oogenic cells and mature oocytes has been described in a deep-sea clam,
Calyptogena pacifica
, for the first time. Specimens were collected in June 2018 from the Piip volcano in ...the Bering Sea (55.3821° N, 167.2613° E). Female germ cells developed in the branched gonadal tubules. The pattern of oogenic development is similar to that in littoral species. Although somatic accessory cells do not form any follicles around developing oocytes, these cells have a well-developed endoplasmic reticulum, which could be a source of yolk precursors and be involved in vitellogenesis. Lipid droplets appear in early oocytes, but they disappear later, suggesting that developing oocytes use these lipid droplets. At the onset of vitellogenesis, developing oocytes accumulate lipids in the ooplasm facing the gonadal tubule wall. Yolk granules, in contrast, appear at later stages of oogenesis. Mature oocytes, which are 200 µm in diameter, are filled with a significant volume of lipid droplets (occupying 24% of ooplasm) and a smaller volume of yolk granules (~ 8%). The mature oocyte’s features, i.e., the large cell size (~ 200 µm in diameter) and the high abundance of ooplasmic inclusions, are typical of species with lecithotrophic development. The large volume of lipid droplets would enhance buoyancy of the oocytes and provide embryos and larvae with nutrients during dispersal. Symbiotic bacteria were found in accessory cells, in vitellogenic oocytes, and within remnants of degenerating oocytes.
Bivalves comprise a large, highly diverse taxon of invertebrate species. Developmental studies of neurogenesis among species of Bivalvia are limited. Due to a lack of neurogenesis information, it is ...difficult to infer a ground pattern for Bivalvia. To provide more comprehensive morphogenetic data on bivalve molluscs and relationships among molluscan clades, we investigated neurogenesis in the Pacific oyster,
, from the appearance of the first sensory cells to the formation of the larval ganglionic nervous system by co-immunocytochemistry of the neuronal markers FMRFamide or 5-HT and vesicular acetylcholine transporter (VAChT).
Neurogenesis begins with the emergence of the apical serotonin-immunoreactive (5-HT-ir) sensory cells and paired sensory posttrochal dorsal and ventral FMRFamide-immunoreactive (FMRFamide-ir) cells at the early trochophore stage. Later, at the early veliger stage, the apical organ (AO) includes 5-HT-ir, FMRFamide-ir, and VAChT-ir cells. At the same stage, VAChT-ir cells appear in the posterior region of larvae and send axons towards the AO. Thus, FMRFamide-ir neurites and VAChT-ir processes form scaffolds for longitudinal neurite bundles develop into the paired ventral nerve cords (VNC). Later-appearing axons from the AO/CG neurons join the neurite bundles comprising the VNC. All larval ganglia appear along the VNC as paired or fused (epiathroid) clusters in late veliger and pediveliger larvae. We observed the transformation of the AO into the cerebral ganglia, which abundantly innervated the velum, and the transformation of ventral neurons into the pedal ganglia, innervating the foot, gills, and anterior adductor muscle. The visceral ganglia appear last in the pediveliger oyster and innervate the visceral mass and posterior adductor of premetamorphic larvae. In addition, a local FMRFamide-ir network was detected in the digestive system of pediveliger larvae. We identified VAChT-ir nervous elements in oyster larvae, which have not been observed previously in molluscs. Finally, we performed a morphology-based comparative analysis of neuronal structures among bivalve, conchiferan, and aculiferan species.
We described the development of the nervous system during the larval development in
. These data greatly advance the currently limited understanding of neurodevelopment in bivalves and mollusks, which has hampered the generation of a ground pattern reconstruction of the last common ancestor of Mollusca. Our morphological data support phylogenomic data indicating a closer Bivalvia-Gastropoda sister group relationship than the Bivalvia-Scaphopoda (Diasoma) group relationship.
Combination of insect pathogenic fungi and microbial metabolites is a prospective method for mosquito control. The effect of the entomopathogenic fungus Metarhizium robertsii J.F. Bischoff, S.A. ...Rehner & Humber and avermectins on the survival and physiological parameters of Aedes aegypti (Linnaeus, 1762) larvae (dopamine concentration, glutathione S-transferase (GST), nonspecific esterases (EST), acid proteases, lysozyme-like, phenoloxidase (PO) activities) was studied. It is shown that the combination of these agents leads to a synergistic effect on mosquito mortality. Colonization of Ae. aegypti larvae by hyphal bodies following water inoculation with conidia is shown for the first time. The larvae affected by fungi are characterized by a decrease in PO and dopamine levels. In the initial stages of toxicosis and/or fungal infection (12 h posttreatment), increases in the activity of insect detoxifying enzymes (GST and EST) and acid proteases are observed after monotreatments, and these increases are suppressed after combined treatment with the fungus and avermectins. Lysozyme-like activity is also most strongly suppressed under combined treatment with the fungus and avermectins in the early stages posttreatment (12 h). Forty-eight hours posttreatment, we observe increases in GST, EST, acid proteases, and lysozyme-like activities under the influence of the fungus and/or avermectins. The larvae affected by avermectins accumulate lower levels of conidia than avermectin-free larvae. On the other hand, a burst of bacterial CFUs is observed under treatment with both the fungus and avermectins. We suggest that disturbance of the responses of the immune and detoxifying systems under the combined treatment and the development of opportunistic bacteria may be among the causes of the synergistic effect.
•Spermatozoa of two basal nemerteans have been studied at the ultrastructural level.•Both species have primitive spermatozoa with ovoid head and five mitochondria.•Acrosomal complex of Sonnenemertes ...cantelli composed of multiple small vesicles.
Nemertea is a phylum of worms with a simple internal morphology; nemerteans’ spermatozoon morphology can be used for their classification and phylogenetic analyses. The aim of the present study was to describe spermatozoa of the nemerteans Hubrechtella juliae and Sonnenemertes cantelli from the basal groups of the class Pilidiophora at the ultrastructure level. Both species have primitive (‘compact-head’ sensu Stricker and Folsom, 1998) spermatozoa with ovoid head and five mitochondria in the midpiece, but differ in the structure of acrosomal complex: in Hubrechtella juliae, the single lens-shaped acrosomal vesicle contains an area of moderate electron density not enclosed by a separate membrane; in Sonnenemertes cantelli, the acrosome shows a unique morphology and contains a few electron-dense vesicles with irregular shapes and positions and one more electron-lucent elongated vesicle. Such a pattern of the acrosomal complex organization is described for Nemertea for the first time. An assumption is made that the states “two or more mitochondria” and “posterior acrosomal ring component” may be synapomorphies of Hubrechtiiformes+Heteronemertea (class Pilidiophora), whereas “the posterior margin of the acrosomes forms an acrosomal ring component” is presumably an autapomorphy of the family Lineidae s.l. The results suggest that spermatozoa provide a useful source of characters for nemertean systematics.
•Interacinar space is filled by hemocytes and muscle cells.•In males, numerous accessory cells are present in pre-spawning acini.•In females, accessory cells do not form follicle around oocytes.
...Somatic cells in the gonadal area of male and female deep-sea clams, Calyptogena pacifica, were examined using light and transmission electron microscopy. Acini both at the pre-spawning stage and at the stage of active spermatogenesis were observed to be simultaneously present in sections through a male gonad. Oocytes of various degrees of maturity were simultaneously present in female acini. No storage tissue and cells similar to adipogranular cells or vesicular connective tissue of other mollusks were found in the gonadal area of C. pacifica. Instead, in both males and females, numerous hemocytes surround the acini. Among hemocytes, two types of granulocytes and erythrocytes were identified. Bundles of muscle cells were also found in the interacinar space. Male intraacinar accessory cells were rather large, glycogen-rich, with lipid inclusions, and phagosomes contained spermatogenic cells. Female accessory cells had well-developed endoplasmic reticulum, but they did not form any follicles around oocytes, being in their basal part, closer to basal lamina. Such a specific pattern of gonad organization can presumably be explained by both symbiosis with sulfide-oxidizing bacteria and phylogenetic aspects that should be further studied. Some evidence for continuous gametogenesis are discussed.
The process of spermatogenesis and spermatozoon morphology was characterized from a deep‐sea bivalve, Calyptogena pacifica (Vesicomyidae, Pliocardiinae), a member of the superfamily Glossoidea, using ...light and electron microscopy. Spermatogenesis in C. pacifica is generally similar to that in shallow‐water bivalves but, the development of spermatogenic cells in this species has also some distinguishing features. First proacrosomal vesicles are observed in early spermatocytes I. Although, early appearance of proacrosomal vesicles is well known for bivalves, in C. pacifica, these vesicles are associated with electron‐dense material, which is located outside the limiting membrane of the proacrosomal vesicles and disappears in late spermatids. Another feature of spermatogenesis in C. pacifica is the localization of the axoneme and flagellum development. Early spermatogenic cells lack typical flagellum, while in spermatogonia, spermatocytes, and early spermatids, the axoneme is observed in the cytoplasm. In late spermatids, the axoneme is located along the nucleus, and the flagellum is oriented anteriorly. During sperm maturation, the bent flagellum is transformed into the typical posteriorly oriented tail. Spermatozoa of C. pacifica are of ect‐aqua sperm type with a bullet‐like head of about 5.8 μm in length and 1.8 μm in width, consisting of a well‐developed dome‐shaped acrosomal complex, an elongated barrel‐shaped nucleus filled with granular chromatin, and a midpiece with mainly four rounded mitochondria. A comparative analysis has shown a number of common traits in C. pacifica and Neotrapezium sublaevigatum.
The spermatogenesis in Calyptogena pacifica is similar to that in shallow‐water bivalves. Proacrosomal vesicles are associated with outer electron‐dense material. The axoneme is located near the nucleus until late spermatid stage.
Recent findings regarding early lophotrochozoan development have altered the conventional model of neurogenesis and revealed that peripheral sensory elements play a key role in the initial ...organization of the larval nervous system. Here, we describe the main neurogenetic events in bivalve mollusks in comparison with other Lophotrochozoa, emphasizing a novel role for early neurons in establishing larval nervous systems and speculating about the morphogenetic function of the apical organ. We demonstrate that during bivalve development, peripheral sensory neurons utilizing various transmitters differentiate before the apical organ emerges. The first neurons and their neurites serve as a scaffold for the development of the nervous system. During veliger stage, cerebral, pleural, and visceral ganglia form along the lateral (visceral) nerve cords in anterior-to-posterior axis. The pedal ganglia and corresponding ventral (pedal) nerve cords develop much later, after larval settlement and metamorphosis. Pharmacological abolishment of the serotonin gradient within the larval body disrupts the navigation of "pioneer" axons resulting in malformation of the whole nervous system architecture. Comparative morphological data on neurogenetic events in bivalve mollusks shed new light on the origin of the nervous system, mechanisms of early axon navigation, and sequence of the tetraneurous nervous system formation. Furthermore, this information improves our understanding of the basic nervous system architecture in larval Bivalvia and Mollusca.
•Number of autophagosomes in nutrient storage cells increases during gametogenesis.•Number of autophagosomes in nutrient storage cells in females is higher than in males.•No destruction of nutrient ...storage cells was observed during gametogenesis.
In oysters, nutrients are stored in a special type of cells referred to as vesicular-connective tissue cells (VCT-cells). These cells accumulate and provide nutrient to satisfy various needs of the organism, including gametogenesis. During the annual reproductive cycle, VCT-cells pass through a series of changes in their morphology associated with nutrients mobilization for developing germ cells. The results presented here show an approximately 33–35% increase in the number of autophagic vesicles in cytoplasm of VCT-cells in the gonadal area of C. gigas during the stage of active gametogenesis as compared to the resting stage of reproductive cycle. No destruction of VCT-cells due to autophagy or any other factors was observed, both in males and females. Our results indicate that autophagy does increase in VCT-cells of C. gigas and plays a certain role in nutrient mobilization from these cells.
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