An acidic microenvironment produced by the V-type ATPase of Euprymna scolopes promotes specificity during Vibrio fischeri recruitment.

Animals often acquire their microbial symbionts from the environment, but the mechanisms underlying how specificity of the association is achieved are poorly understood. We demonstrate that the conserved proton pump, V-type ATPase (VHA), plays a key role in the establishment of the model light-organ symbiosis between the squid Euprymna scolopes and its bacterial partner, Vibrio fischeri. Recruitment of V.

Soluble adenylyl cyclase is an acid-base sensor in rainbow trout red blood cells that regulates intracellular pH and haemoglobin-oxygen binding.

Aim: To identify the physiological role of the acid-base sensing enzyme, soluble adenylyl cyclase (sAC), in red blood cells (RBC) of the model teleost fish, rainbow trout.

Methods: We used: (i) super-resolution microscopy to determine the subcellular location of sAC protein; (ii) live-cell imaging of RBC intracellular pH (pH) with specific sAC inhibition (KH7 or LRE1) to determine its role in cellular acid-base regulation; (iii) spectrophotometric measurements of haemoglobin-oxygen (Hb-O) binding in steady-state conditions; and (iv) during simulated arterial-venous transit, to determine the role of sAC in systemic O transport.

Results: Distinct pools of sAC protein were detected in the RBC cytoplasm, at the plasma membrane and within the nucleus.

Immunohistochemical and ultrastructural characterization of the inner ear epithelial cells of splitnose rockfish ().

The inner ear of teleost fish regulates the ionic and acid-base chemistry and secretes protein matrix into the endolymph to facilitate otolith biomineralization, which is used to maintain vestibular and auditory functions. The otolith is biomineralized in a concentric ring pattern corresponding to seasonal growth, and this calcium carbonate (CaCO) polycrystal has become a vital aging and life-history tool for fishery managers, ecologists, and conservation biologists. Moreover, biomineralization patterns are sensitive to environmental variability including climate change, thereby threatening the accuracy and relevance of otolith-reliant toolkits.

A novel perspective on the evolutionary loss of plasma-accessible carbonic anhydrase at the teleost gill.

The gills of most teleost fishes lack plasma-accessible carbonic anhydrase (paCA) that could participate in CO2 excretion. We tested the prevailing hypothesis that paCA would interfere with red blood cell (RBC) intracellular pH regulation by β-adrenergic sodium-proton exchangers (β-NHE) that protect pH-sensitive haemoglobin-oxygen (Hb-O2) binding during an acidosis. In an open system that mimics the gills, β-NHE activity increased Hb-O2 saturation during a respiratory acidosis in the presence or absence of paCA, whereas the effect was abolished by NHE inhibition.

Evolving views of ionic, osmotic and acid-base regulation in aquatic animals.

The regulation of ionic, osmotic and acid-base (IOAB) conditions in biological fluids is among the most fundamental functions in all organisms; being surrounded by water uniquely shapes the IOAB regulatory strategies of water-breathing animals. Throughout its centennial history, Journal of Experimental Biology has established itself as a premier venue for publication of comparative, environmental and evolutionary studies on IOAB regulation. This Review provides a synopsis of IOAB regulation in aquatic animals, some of the most significant research milestones in the field, and evolving views about the underlying cellular mechanisms and their evolutionary implications.

The V-type ATPase enhances photosynthesis in marine phytoplankton and further links phagocytosis to symbiogenesis.

Diatoms, dinoflagellates, and coccolithophores are dominant groups of marine eukaryotic phytoplankton that are collectively responsible for the majority of primary production in the ocean. These phytoplankton contain additional intracellular membranes around their chloroplasts, which are derived from ancestral engulfment of red microalgae by unicellular heterotrophic eukaryotes that led to secondary and tertiary endosymbiosis. However, the selectable evolutionary advantage of these membranes and the physiological significance for extant phytoplankton remain poorly understood.

Distinct genomic routes underlie transitions to specialised symbiotic lifestyles in deep-sea annelid worms.

Bacterial symbioses allow annelids to colonise extreme ecological niches, such as hydrothermal vents and whale falls. Yet, the genetic principles sustaining these symbioses remain unclear. Here, we show that different genomic adaptations underpin the symbioses of phylogenetically related annelids with distinct nutritional strategies.

Effects of ocean acidification on dopamine-mediated behavioral responses of a coral reef damselfish.

We investigated whether CO-induced ocean acidification (OA) affects dopamine receptor-dependent behavior in bicolor damselfish (Stegastes partitus). Damselfish were kept in aquaria receiving flow through control (pH ~ 8.03; pCO ~ 384 μatm) or OA (pH ~ 7.

Soluble adenylyl cyclase coordinates intracellular pH homeostasis and biomineralization in calcifying cells of a marine animal.

Biomineralizing cells concentrate dissolved inorganic carbon (DIC) and remove protons from the site of mineral precipitation. However, the molecular regulatory mechanisms that orchestrate pH homeostasis and biomineralization of calcifying cells are poorly understood. Here, we report that the acid-base sensing enzyme soluble adenylyl cyclase (sAC) coordinates intracellular pH (pH) regulation in the calcifying primary mesenchyme cells (PMCs) of sea urchin larvae.

Optimizing immunostaining of archival fish samples to enhance museum collection potential.

Immunohistochemistry (IHC) is a powerful biochemical technique that uses antibodies to specifically label and visualize proteins of interests within biological samples. However, fluid-preserved specimens within natural history collection often use fixatives and protocols that induce high background signal (autofluorescence), which hampers IHC as it produces low signal-to-noise ratio. Here, we explored techniques to reduce autofluorescence using sodium borohydride (SBH), citrate buffer, and their combination on fish tissue preserved with paraformaldehyde, formaldehyde, ethanol, and glutaraldehyde.

Dining on the dead in the deep: Active NH excretion via Na /H (NH ) exchange in the highly ammonia tolerant Pacific hagfish, Eptatretus stoutii.

Aim: Pacific hagfish are exceptionally tolerant to high environmental ammonia (HEA). Here, we elucidated a cellular mechanism that enables hagfish to actively excrete ammonia against steep ammonia gradients expected to be found inside a decomposing whale carcass.

Methods: Hagfish were exposed to varying concentrations of HEA in the presence or absence of environmental Na , while plasma ammonia levels were tracked.

The silent loss of cell physiology hampers marine biosciences.

An ongoing loss of experts in marine cellular biochemistry and physiology (CBP) is stagnating the generation of knowledge upon which rapidly growing "omics" approaches rely, ultimately hampering our ability to predict organismal responses to climate change.

A Rhesus channel in the coral symbiosome membrane suggests a novel mechanism to regulate NH and CO delivery to algal symbionts.

Reef-building corals maintain an intracellular photosymbiotic association with dinoflagellate algae. As the algae are hosted inside the symbiosome, all metabolic exchanges must take place across the symbiosome membrane. Using functional studies in oocytes, immunolocalization, and confocal Airyscan microscopy, we established that Rh (ayRhp1) facilitates transmembrane NH and CO diffusion and that it is present in the symbiosome membrane.

Elucidating the acid-base mechanisms underlying otolith overgrowth in fish exposed to ocean acidification.

Over a decade ago, ocean acidification (OA) exposure was reported to induce otolith overgrowth in teleost fish. This phenomenon was subsequently confirmed in multiple species; however, the underlying physiological causes remain unknown. Here, we report that splitnose rockfish (Sebastes diploproa) exposed to ~1600 μatm pCO(pH ~7.

V-type H-ATPase in the symbiosome membrane is a conserved mechanism for host control of photosynthesis in anthozoan photosymbioses.

In reef-building corals (order Scleractinia) and giant clams (phylum Molluca), V-type H-ATPase (VHA) in host cells is part of a carbon concentrating mechanism (CCM) that regulates photosynthetic rates of their symbiotic algae. Here, we show that VHA plays a similar role in the sea anemone , a member of the order Actinaria and sister group to the Scleractinia, which in contrast to their colonial calcifying coral relatives is a solitary, soft-bodied taxa. Western blotting and immunofluorescence revealed that VHA was abundantly present in the host-derived symbiosome membrane surrounding the photosymbionts.

A pH-powered mechanochemical engine regulates the buoyancy of Chaoborus midge larvae.

The freshwater aquatic larvae of the Chaoborus midge are the world's only truly planktonic insects, regulating their buoyancy using two pairs of internal air-filled sacs, one in the thorax and the other in the seventh abdominal segment. In 1911, August Krogh demonstrated the larvae's ability to control their buoyancy by exposing them to an increase in hydrostatic pressure. However, how these insects control the volume of their air-sacs has remained a mystery.

Rapid blood acid-base regulation by European sea bass (Dicentrarchus labrax) in response to sudden exposure to high environmental CO2.

Fish in coastal ecosystems can be exposed to acute variations in CO2 of between 0.2 and 1 kPa CO2 (2000-10,000 µatm). Coping with this environmental challenge will depend on the ability to rapidly compensate for the internal acid-base disturbance caused by sudden exposure to high environmental CO2 (blood and tissue acidosis); however, studies about the speed of acid-base regulatory responses in marine fish are scarce.

A novel K -dependent Na uptake mechanism during low pH exposure in adult zebrafish (Danio rerio): New tricks for old dogma.

Aim: To determine whether Na uptake in adult zebrafish (Danio rerio) exposed to acidic water adheres to traditional models reliant on Na /H Exchangers (NHEs), Na channels and Na /Cl Cotransporters (NCCs) or if it occurs through a novel mechanism.

Methods: Zebrafish were exposed to control (pH 8.0) or acidic (pH 4.

Adrenergically induced translocation of red blood cell β-adrenergic sodium-proton exchangers has ecological relevance for hypoxic and hypercapnic white seabass.

White seabass () increasingly experience periods of low oxygen (O; hypoxia) and high carbon dioxide (CO, hypercapnia) due to climate change and eutrophication of the coastal waters of California. Hemoglobin (Hb) is the principal O carrier in the blood and in many teleost fishes Hb-O binding is compromised at low pH; however, the red blood cells (RBC) of some species regulate intracellular pH with adrenergically stimulated sodium-proton-exchangers (β-NHEs). We hypothesized that RBC β-NHEs in white seabass are an important mechanism that can protect the blood O-carrying capacity during hypoxia and hypercapnia.

Ion-transporting capacity and aerobic respiration of larval white seabass (Atractoscion nobilis) may be resilient to ocean acidification conditions.

Ocean acidification (OA) has been proposed to increase the energetic demand for acid-base regulation at the expense of larval fish growth. Here, white seabass (Atractoscion nobilis) eggs and larvae were reared at control (542 ± 28 μatm) and elevated pCO (1831 ± 105 μatm) until five days post-fertilization (dpf). Skin ionocytes were identified by immunodetection of the Na/K-ATPase (NKA) enzyme.

Changes in gill and air-breathing organ characteristics during the transition from water- to air-breathing in juvenile Arapaima gigas.

The obligate air-breathing Amazonian fish, Arapaima gigas, hatch as water-breathing larvae but with development, they modify their swim bladder to an air-breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO.

The dose makes the poison: Non-linear behavioural response to CO-induced aquatic acidification in zebrafish (Danio rerio).

CO-induced aquatic acidification is predicted to affect fish neuronal GABA receptors leading to widespread behavioural alterations. However, the large variability in the magnitude and direction of behavioural responses suggests substantial species-specific CO threshold differences, life history and parental acclimation effects, experimental artifacts, or a combination of these factors. As an established model organism, zebrafish (Danio rerio) can be reared under stable conditions for multiple generations, which may help control for some of the variability observed in wild-caught fishes.

Molecular and biochemical characterization of the bicarbonate-sensing soluble adenylyl cyclase from a bony fish, the rainbow trout .

Soluble adenylyl cyclase (sAC) is a -stimulated enzyme that produces the ubiquitous signalling molecule cAMP, and deemed an evolutionarily conserved acid-base sensor. However, its presence is not yet confirmed in bony fishes, the most abundant and diverse of vertebrates. Here, we identified sAC genes in various cartilaginous, ray-finned and lobe-finned fish species.