Osmoregulated Chloride Currents in Hemocytes from Mytilus galloprovincialis

Short communication: ROS production and mitochondrial membrane potential in hemocytes of marine bivalves, Mytilus galloprovincialis and Magallana gigas, under hypoosmotic stress

Bivalve mollusks that inhabit low-depth coastal and estuarine areas frequently experience osmotic stress that may be also associated with alterations of antioxidant enzyme activities and markers of oxidative stress. Mitochondria are a major source of reactive oxygen species (ROS) in eucaryotic cells. Overpoduction of ROS induces oxidative stress leading to a damage of intracellular compartments and cell death. In euryhaline bivalves, information concerning cellular ROS production upon osmotic stress and changes in mitochondrial membrane potential is scarce. The present study investigates osmotic stability and hemocytes` regulatory volume decrease (RVD) of Mediterranean mussel (Mytilus galloprovincialis) and the Pacific oyster (Magallana gigas). We also studied dynamic changes in intracellular ROS levels and mitochondrial membrane potential in hemocytes undergoing the RVD response following hypoosmotic swelling. Our data revealed that osmotic stability of mussel and oyster hemocytes did not significantly differ. Loss of environmental osmolarity from 460.0 ± 2.0 mOsm l-1 to 216.0 ± 4.0 mOsm l-1 resulted in an increase of hemocyte volume by 60% of the initial cellular volume in mussels and by 28% in oysters. After rapid hypoosmotic swelling hemocytes of both species demonstrated the RVD response. At the end of 60 min exposure to hypoosmotic environment, hemocyte volume significantly decreased in both species by 10-12% compared to the maximal hemocyte volume. Hypoosmotic shock induced an increase of mitochondrial membrane potential in hemocytes of mussels and oysters. In mussels, increased mitochondrial membrane potential was accompanied with decreased ROS levels in hemocytes, whereas oyster hemocytes showed enhanced ROS production.

Effect of hypersalinic stress on hemocyte morphology and hemolymph cellular composition of the ark clam (Anadarakagoshimensis)

Bivalve mollusks as typical osmoconformers are unable to maintain a constant level of internal osmolarity in conditions of salinity stress. Adaptation to fluctuations of environmental salinity is achieved through cellular osmoregulatory responses, which are accompanied with a substantial shift in functional state of cells. In the present work we investigated the effect of hypersalinity stress on hemolymph cellular composition and morphology of the ark clam (Anadara kagoshimensis) hemocytes. Ark clams were subjected to a gradual increase of environmental salinity from 18‰ to 35‰ and 45‰ and maintained at those conditions for two days. Exposure to hypersalinity 35‰ induced changes in erythrocyte morphology and led to a decrease of their diameter. At salinity 45‰ a substantial increase of hemocyte average diameter was observed, whereas the shape of cells did not change (18‰). Hyperosmotic stress was not associated with changes in hemocyte viability as well as changes in hemolymph cellular composition. The results of the present work demonstrate high tolerance of A. kagoshimensis to short-time exposure to hypersalinic conditions.

Cellular osmoregulation of the ark clam (Anadara kagoshimensis) hemocytes to hyposmotic media

Many bivalve species are considered to be euryhaline organisms due to effective adaptation to fluctuations of environmental salinity. Cellular mechanisms responsible for tolerance to salinity changes remain unclear for bivalves despite this question being critically important for commercially cultured species frequently introduced into regions differing from natural habitat by salinity regime. In the present work laser diffraction method was used for the analysis of volume changes in hemoglobin-containing ark clam (Anadara kagoshimensis) hemocytes following hyposmotic stimulation. Hemocytes responded to hyposmotic shock (decrease of media osmolarity from 461 to 216 mОsm/L) by a rapid swelling up to 171.5 ± 15.2% of control level. At normal osmotic conditions (osmolarity 461 mOsm/L), hemocyte mean cellular volume (MCV) was 354.0 ± 24.4 fl and maximum MCV of hyposmotically swollen cells prior lysis was 555.5 ± 57.4 fl (at the osmolarity 194 mOsm/L). Ark clam hemocytes demonstrated volume recovery response following hyposmotic swelling. Regulatory volume decrease (RVD) reaction did not depend on hemoglobin confirmation status. Final MCV of swollen hemocytes at the end of experimental period of RVD in oxygenated and deoxygenated suspensions did not significantly differ.

Effects of Exposure to Trade Antifouling Paints and Biocides on Larval Settlement and Metamorphosis of the Compound Ascidian Botryllus schlosseri

To evaluate the effects of antifouling paints and biocides on larval settlement and metamorphosis, newly hatched swimming larvae of the compound ascidian Botryllus schlosseri, a dominant species of soft-fouling in coastal communities, were exposed to (i) substrata coated with seven antifouling paints on the market containing different biocidal mixtures and types of matrices and (ii) sea water containing various concentrations of eight biocidal constituents. All antifouling paints showed high performance, causing 100% mortality and metamorphic inhibition, with ≥75% not-settled dead larvae. All antifouling biocides prevented the settlement of larvae. The most severe larval malformations, i.e., (i) the formation of a bubble encasing the cephalenteron and (ii) the inhibition of tail resorption, were observed after exposure to metal and organometal compounds, including tributyltin (TBT) at 1 μM (325.5 µg L−1), zinc pyrithione (ZnP) at 1 μM (317.7 µg L−1), and CuCl at 0.1 μM (98.99 µg L−1), and to antimicrobials and fungicides, including Sea-Nine 211 at 1 μM (282.2 µg L−1) and Chlorothalonil at 1 μM (265.9 µg L−1). The herbicides seemed to be less active. Irgarol 1051 was not lethal at any of the concentrations tested. Diuron at 250 μM (58.2 mg L−1) and 2,3,5,6-tetrachloro-4-(methylsulphonyl)pyridine (TCMS pyridine) at 50 μM (14.8 mg L−1) completely inhibited larval metamorphosis. These results may have important implications for the practical use of different antifouling components, highlighting the importance of their testing for negative impacts on native benthic species.

Chromosome-level genome and population genomic analysis provide insights into the evolution and environmental adaptation of Jinjiang oyster Crassostrea ariakensis

The Jinjiang oyster Crassostrea ariakensis, naturally distributing in estuarine regions with low salinity, is an important economic and ecological species in China. However, studies on its genomics and population genetics remain lacking. Here, we assembled the chromosome-level genome of a female C. ariakensis and re-sequenced 261 individuals from five locations in China representing three typical habitats. The C. ariakensis genome was 662.9 Mb with contig N50 length of 5.9 Mb using PacBio HiFi-CCS long reads, and 99.83% sequences were anchored onto 10 pseudochromosomes using Hi-C data. A total of 26,354 protein-coding genes were predicted. We identified three significantly expanded gene families which are closely associated with osmotic pressure regulation, including CDO, SLC13 and SDR. Population structure analysis revealed that the C. ariakensis from five locations were clustered into three typical groups (northern, southern and Shanghai) (K = 3) and their phylogenetic relationship was consistently correlated to their geographical distribution. Furtherly, the differentiation between northern and southern groups was clearly demonstrated by estimated population differentiation coefficient (F_ST  = 0.1154), and the PSMC distribution showed the two groups of effective population size separated at 0.1 Ma. Meanwhile gene flow from southern to Shanghai was detected. Selective sweep analysis between northern and southern group detected genes associated with heat response and salinity adaptation. This study could provide valuable genomic resources and information for further research on the molecular evolution, genetic breeding, biological function and evolutionary adaptation of C. ariakensis.

IMPACT OF LOW SALINITY ON HEMOCYTES MORPHOLOGY AND FUNCTIONAL ASPECTS IN INVASIVE CLAM ANADARA KAGOSHIMENSIS (TOKUNAGA, 1906)

Impact of low salinity on morphology and function of hemocytes in ark clam species Anadara kagoshimensis was investigated using light microscopy and flow cytometry. In control group the water salinity was adjusted to 19.6‰, and experimental group was maintained at 14.8‰ and 8.8‰. Two cell types, amebocytes and erythrocytes, were identified in control group of ark clams. Erythrocytes constituted the main type of the cells, and amounted to 92.3±3.9 %. Hyposalinity changed that proportion: the number of amebocytes decreased 2.7 times and number of erythrocytes increased 7.6 times. Morphometric characteristics of hemocytes didn’t show statistically significant changes. As far as salinity decreased, the number of erythrocyte shades in hemolymph increased (3.5 times at salinity 8.8‰) and, in hemocytes, the reactive oxygen species (ROS) production grew (3.5. times at salinity 8.8‰).

A perspective on the modulation of plant and animal two pore channels (TPCs) by the flavonoid naringenin

The inhibitory effect of the flavonoid naringenin on plant and human Two-Pore Channels (TPCs) was assessed by means of electrophysiological measurements. By acting on human TPC2, naringenin, was able to dampen intracellular calcium responses to VEGF in cultured human endothelial cells and to impair angiogenic activity in VEGF-containing matrigel plugs implanted in mice. Molecular docking predicts selective binding sites for naringenin in the TPC structure, thus suggesting a specific interaction between the flavonoid and the channel.