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Nern A, Lösche F, Takemura SY, Burnett LE, Dreher M, Gruntman E, Hoeller J, Huang GB, Januszewski M, Klapoetke NC, Koskela S, Longden KD, Lu Z, Preibisch S, Qiu W, Rogers EM, Seenivasan P, Zhao A, Bogovic J, Canino BS, Clements J, Cook M, Finley-May S, Flynn MA, Hameed I, Hayworth KJ, Hopkins GP, Hubbard PM, Katz WT, Kovalyak J, Lauchie SA, Leonard M, Lohff A, Maldonado CA, Mooney C, Okeoma N, Olbris DJ, Ordish C, Paterson T, Phillips EM, Pietzsch T, Salinas JR, Rivlin PK, Scott AL, Scuderi LA, Takemura S, Talebi I, Thomson A, Trautman ET, Umayam L, Walsh C, Walsh JJ, Shan Xu C, Yakal EA, Yang T, Zhao T, Funke J, George R, Hess HF, Jefferis GSXE, Knecht C, Korff W, Plaza SM, Romani S, Saalfeld S, Scheffer LK, Berg S, Rubin GM, Reiser MB. Connectome-driven neural inventory of a complete visual system. bioRxiv 2024:2024.04.16.589741. [PMID: 38659887 PMCID: PMC11042306 DOI: 10.1101/2024.04.16.589741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/26/2024]
Abstract
Vision provides animals with detailed information about their surroundings, conveying diverse features such as color, form, and movement across the visual scene. Computing these parallel spatial features requires a large and diverse network of neurons, such that in animals as distant as flies and humans, visual regions comprise half the brain's volume. These visual brain regions often reveal remarkable structure-function relationships, with neurons organized along spatial maps with shapes that directly relate to their roles in visual processing. To unravel the stunning diversity of a complex visual system, a careful mapping of the neural architecture matched to tools for targeted exploration of that circuitry is essential. Here, we report a new connectome of the right optic lobe from a male Drosophila central nervous system FIB-SEM volume and a comprehensive inventory of the fly's visual neurons. We developed a computational framework to quantify the anatomy of visual neurons, establishing a basis for interpreting how their shapes relate to spatial vision. By integrating this analysis with connectivity information, neurotransmitter identity, and expert curation, we classified the ~53,000 neurons into 727 types, about half of which are systematically described and named for the first time. Finally, we share an extensive collection of split-GAL4 lines matched to our neuron type catalog. Together, this comprehensive set of tools and data unlock new possibilities for systematic investigations of vision in Drosophila, a foundation for a deeper understanding of sensory processing.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | - Gregory SXE Jefferis
- MRC Laboratory of Molecular Biology, Cambridge, UK and Department of Zoology, University of Cambridge, UK
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Hao MM, Bergner AJ, Nguyen HTH, Dissanayake P, Burnett LE, Hopkins CD, Zeng K, Young HM, Stamp LA. Role of JNK, MEK and adenylyl cyclase signalling in speed and directionality of enteric neural crest-derived cells. Dev Biol 2019; 455:362-368. [PMID: 31306639 DOI: 10.1016/j.ydbio.2019.07.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2019] [Revised: 07/11/2019] [Accepted: 07/11/2019] [Indexed: 12/28/2022]
Abstract
BACKGROUND Cells derived from the neural crest colonize the developing gut and give rise to the enteric nervous system. The rate at which the ENCC population advances along the bowel will be affected by both the speed and directionality of individual ENCCs. The aim of the study was to use time-lapse imaging and pharmacological activators and inhibitors to examine the role of several intracellular signalling pathways in both the speed and the directionality of individual enteric neural crest-derived cells in intact explants of E12.5 mouse gut. Drugs that activate or inhibit intracellular components proposed to be involved in GDNF-RET and EDN3-ETB signalling in ENCCs were used. FINDINGS Pharmacological inhibition of JNK significantly reduced ENCC speed but did not affect ENCC directionality. MEK inhibition did not affect ENCC speed or directionality. Pharmacological activation of adenylyl cyclase or PKA (a downstream cAMP-dependent kinase) resulted in a significant decrease in ENCC speed and an increase in caudal directionality of ENCCs. In addition, adenylyl cyclase activation also resulted in reduced cell-cell contact between ENCCs, however this was not observed following PKA activation, suggesting that the effects of cAMP on adhesion are not mediated by PKA. CONCLUSIONS JNK is required for normal ENCC migration speed, but not directionality, while cAMP signalling appears to regulate ENCC migration speed, directionality and adhesion. Collectively, our data demonstrate that intracellular signalling pathways can differentially affect the speed and directionality of migrating ENCCs.
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Affiliation(s)
- Marlene M Hao
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Annette J Bergner
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Huynh T H Nguyen
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Paige Dissanayake
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Laura E Burnett
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - C Danielle Hopkins
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Kevin Zeng
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Heather M Young
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
| | - Lincon A Stamp
- Department of Anatomy and Neuroscience, University of Melbourne, Melbourne, Victoria, Australia.
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Beattie R, Postiglione MP, Burnett LE, Laukoter S, Streicher C, Pauler FM, Xiao G, Klezovitch O, Vasioukhin V, Ghashghaei TH, Hippenmeyer S. Mosaic Analysis with Double Markers Reveals Distinct Sequential Functions of Lgl1 in Neural Stem Cells. Neuron 2017; 94:517-533.e3. [PMID: 28472654 DOI: 10.1016/j.neuron.2017.04.012] [Citation(s) in RCA: 60] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Revised: 03/02/2017] [Accepted: 04/05/2017] [Indexed: 11/17/2022]
Abstract
The concerted production of neurons and glia by neural stem cells (NSCs) is essential for neural circuit assembly. In the developing cerebral cortex, radial glia progenitors (RGPs) generate nearly all neocortical neurons and certain glia lineages. RGP proliferation behavior shows a high degree of non-stochasticity, thus a deterministic characteristic of neuron and glia production. However, the cellular and molecular mechanisms controlling RGP behavior and proliferation dynamics in neurogenesis and glia generation remain unknown. By using mosaic analysis with double markers (MADM)-based genetic paradigms enabling the sparse and global knockout with unprecedented single-cell resolution, we identified Lgl1 as a critical regulatory component. We uncover Lgl1-dependent tissue-wide community effects required for embryonic cortical neurogenesis and novel cell-autonomous Lgl1 functions controlling RGP-mediated glia genesis and postnatal NSC behavior. These results suggest that NSC-mediated neuron and glia production is tightly regulated through the concerted interplay of sequential Lgl1-dependent global and cell intrinsic mechanisms.
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Affiliation(s)
- Robert Beattie
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Maria Pia Postiglione
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Laura E Burnett
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Susanne Laukoter
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Carmen Streicher
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Florian M Pauler
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria
| | - Guanxi Xiao
- Department of Molecular Biomedical Sciences, Program in Genetics, W.M. Keck Center for Behavioral Biology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Olga Klezovitch
- Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Valeri Vasioukhin
- Division of Human Biology, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Troy H Ghashghaei
- Department of Molecular Biomedical Sciences, Program in Genetics, W.M. Keck Center for Behavioral Biology, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27607, USA
| | - Simon Hippenmeyer
- Institute of Science and Technology Austria, Am Campus 1, 3400 Klosterneuburg, Austria.
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McCann CJ, Cooper JE, Natarajan D, Jevans B, Burnett LE, Burns AJ, Thapar N. Transplantation of enteric nervous system stem cells rescues nitric oxide synthase deficient mouse colon. Nat Commun 2017; 8:15937. [PMID: 28671186 PMCID: PMC5500880 DOI: 10.1038/ncomms15937] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2016] [Accepted: 04/28/2017] [Indexed: 12/12/2022] Open
Abstract
Enteric nervous system neuropathy causes a wide range of severe gut motility disorders. Cell replacement of lost neurons using enteric neural stem cells (ENSC) is a possible therapy for these life-limiting disorders. Here we show rescue of gut motility after ENSC transplantation in a mouse model of human enteric neuropathy, the neuronal nitric oxide synthase (nNOS−/−) deficient mouse model, which displays slow transit in the colon. We further show that transplantation of ENSC into the colon rescues impaired colonic motility with formation of extensive networks of transplanted cells, including the development of nNOS+ neurons and subsequent restoration of nitrergic responses. Moreover, post-transplantation non-cell-autonomous mechanisms restore the numbers of interstitial cells of Cajal that are reduced in the nNOS−/− colon. These results provide the first direct evidence that ENSC transplantation can modulate the enteric neuromuscular syncytium to restore function, at the organ level, in a dysmotile gastrointestinal disease model. Isolated human and mouse enteric nervous system stem cells (ENSCs) are capable of integrating and promoting innervation of the mouse colon. Here the authors show that transplantation of mouse ENSCs into a mouse model of human enteric neuropathy restores colon motility.
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Affiliation(s)
- Conor J McCann
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
| | - Julie E Cooper
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
| | - Dipa Natarajan
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
| | - Benjamin Jevans
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
| | - Laura E Burnett
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
| | - Alan J Burns
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK.,Department of Clinical Genetics, Erasmus Medical Center, Rotterdam 3015 CN, The Netherlands
| | - Nikhil Thapar
- Stem Cells and Regenerative Medicine, UCL Great Ormond Street Institute of Child Health, 30 Guilford Street, London WC1N, UK
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Garcia RN, Chung KW, Key PB, Burnett LE, Coen LD, Delorenzo ME. Interactive effects of mosquito control insecticide toxicity, hypoxia, and increased carbon dioxide on larval and juvenile eastern oysters and hard clams. Arch Environ Contam Toxicol 2014; 66:450-62. [PMID: 24531857 DOI: 10.1007/s00244-014-0002-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 01/27/2014] [Indexed: 05/13/2023]
Abstract
Mosquito control insecticide use in the coastal zone coincides with the habitat and mariculture operations of commercially and ecologically important shellfish species. Few data are available regarding insecticide toxicity to shellfish early life stages, and potential interactions with abiotic stressors, such as low oxygen and increased CO2 (low pH), are less understood. Toxicity was assessed at 4 and 21 days for larval and juvenile stages of the Eastern oyster, Crassostrea virginica, and the hard clam, Mercenaria mercenaria, using two pyrethroids (resmethrin and permethrin), an organophosphate (naled), and a juvenile growth hormone mimic (methoprene). Acute toxicity (4-day LC50) values ranged from 1.59 to >10 mg/L. Overall, clams were more susceptible to mosquito control insecticides than oysters. Naled was the most toxic compound in oyster larvae, whereas resmethrin was the most toxic compound in clam larvae. Mortality for both species generally increased with chronic insecticide exposure (21-day LC50 values ranged from 0.60 to 9.49 mg/L). Insecticide exposure also caused sublethal effects, including decreased swimming activity after 4 days in larval oysters (4-day EC50 values of 0.60 to 2.33 mg/L) and decreased growth (shell area and weight) in juvenile clams and oysters after 21 days (detected at concentrations ranging from 0.625 to 10 mg/L). Hypoxia, hypercapnia, and a combination of hypoxia and hypercapnia caused mortality in larval clams and increased resmethrin toxicity. These data will benefit both shellfish mariculture operations and environmental resource agencies as they manage the use of mosquito control insecticides near coastal ecosystems.
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Affiliation(s)
- R N Garcia
- Grice Marine Laboratory, College of Charleston, Charleston, SC, 29412, USA
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Boleza KA, Burnett LE, Burnett KG. Hypercapnic hypoxia compromises bactericidal activity of fish anterior kidney cells against opportunistic environmental pathogens. Fish Shellfish Immunol 2001; 11:593-610. [PMID: 11592587 DOI: 10.1006/fsim.2001.0339] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Acute hypoxia can cause massive fish and shellfish mortality. Less clear is the role that chronic sublethal hypoxia might play in aquatic animal health. This study tested whether production of reactive oxygen species (ROS) and bactericidal activity of fish phagocytic cells are suppressed under the conditions of decreased oxygen and pH and increased carbon dioxide which occur in the blood and tissue of animals exposed to sublethal hypoxia. Anterior head kidney (AHK) cells of the mummichog, Fundulus heteroclitus, were exposed in parallel to normoxic (pO2=45 torr, pCO2=3.8 torr, pH=7.6) or hypoxic (pO2=15 torr, pCO2=8.0 torr, pH=7.0) conditions and stimulated with a yeast cell wall extract, zymosan. or live Vibrio parahaemolyticus. Hypercapnic hypoxia suppressed zymosan-stimulated ROS production by 76.0% as measured in the chemiluminescence assay and by 58.5% in the nitroblue tetrazolium (NBT) assay. The low O2, high CO2 and low pH conditions also suppressed superoxide production by 75.0 and 47.3% as measured by the NBT assay at two different challenge ratios of cells:bacteria (1:1 and 1:10, respectively). In addition to its effects on ROS production, hypercapnic hypoxia also reduced bactericidal activity by 23.6 and 72.5% at the 1:1 and 1:10 challenge ratios, respectively. Low oxygen levels alone (pO2=15 torr, pCO2=0.76 torr, pH=7.6) did not significantly compromise the killing activity of cells challenged with equal numbers of V. parahaemolyticus. At the higher 1:10 AHK:bacteria challenge ratio, low oxygen caused a small (26.3%) but significant suppression of bactericidal activity as compared to aerial conditions (pO2=155 torr, pCO2=0.76 torr, pH=7.6). This study demonstrates that while hypoxia alone has detrimental effects on immune function, suppression of phagocytic cell activity is compounded by naturally occurring conditions of hypercapnia and low pH, creating conditions that might be exploited by opportunistic pathogens. These results indicate that the adverse health effects of chronic hypercapnic hypoxia might greatly exceed the effects of low oxygen alone.
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Affiliation(s)
- K A Boleza
- Department of Microbiology and Immunology, Medical University of South Carolina, Charleston 29412, USA
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Willson LL, Burnett LE. Whole animal and gill tissue oxygen uptake in the Eastern oyster, Crassostrea virginica: Effects of hypoxia, hypercapnia, air exposure, and infection with the protozoan parasite Perkinsus marinus(1). J Exp Mar Biol Ecol 2000; 246:223-240. [PMID: 10713278 DOI: 10.1016/s0022-0981(99)00183-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The Eastern oyster, Crassostrea virginica, lives in shallow coastal waters and experiences many different environmental extremes including hypoxia, hypercapnia and air exposure and many oysters are infected with the protozoan parasite Perkinsus marinus. The effects of these conditions on oyster metabolism, as measured by oxygen uptake, were investigated. Mild hypercapnia had no effect on the ability of oysters to regulate oxygen uptake in hypoxic water, as measured by the B2 coefficient of oxygen regulation. The average B2 was -0.060x10(-3) (+/-0.01x10(-3) S.E.M.; n=20; low and high CO(2) treatments combined) in oysters uninfected with P. marinus and -0.056x10(-3) (+/-0.01x10(-3) S.E.M.; n=16; low and high CO(2) treatments combined) in infected oysters. There was no significant effect of light to moderate infections of P. marinus on oxygen regulation. Nor did the presence of P. marinus have an effect on the rate of oxygen uptake of whole animals in well-aerated water. In well-aerated conditions, oxygen uptake was significantly reduced by moderate hypercapnia in oysters when data from uninfected and infected oysters were combined. Mean oxygen uptake of infected oysters under hypercapnia (pCO(2)=6-8 Torr; pH 7) was 9.10 µmol O(2) g ww(-1) h(-1) +/-0.62 S.E.M. (n=9), significantly different from oxygen uptake under normocapnia (pCO(2) </=1 Torr; pH 8.2) (10.71 µmol O(2) g ww(-1) h(-1) +/-0.62 S.E.M.; n=9). Similar to what occurred in infected whole animals, mean oxygen uptake of uninfected gill tissues under high CO(2), low pH conditions was 9.44 µmol O(2) g ww(-1) h(-1) +/-0.95 S.E.M. (n=10), significantly different from oxygen uptake under low CO(2), high pH conditions (12.30 µmol O(2) g ww(-1) h(-1) +/-0.95 S.E.M.; n=10). This result is due primarily to the low pH induced by hypercapnia rather than a CO(2)-specific effect. The presence of P. marinus had no effect on oxygen uptake in gill tissues. Intertidal oysters from South Carolina take up very little oxygen from the air when they are air exposed. Mean oxygen uptake in air at 25 degrees C (5.66x10(-4) µmol O(2) g ww(-1) h(-1)+/-2.65x10(-4) S.E.M.; n=11) is less than 0.1% of oxygen uptake in seawater, suggesting that upon air exposure, oysters close their valves and isolate themselves from air. Oxygen uptake in air is slightly elevated at 35 degrees C (9.28x10(-4) µmol O(2) g ww(-1) h(-1) +/-5.57x10(-4) S.E.M.; n=11). There was not a strong correlation between oxygen uptake and P. marinus infection intensity at either 25 or 35 degrees C.
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Affiliation(s)
- LL Willson
- Grice Marine Laboratory, University of Charleston, South Carolina, 205 Fort Johnson, Charleston, SC, USA
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Abstract
Oysters are frequently exposed to severely hypoxic conditions, especially during summer months. During the summer, there are also large numbers of disease-related oyster mortalities. This research was conducted to determine whether exposure to environmental hypoxia reduces the ability of oyster hemocytes to produce reactive oxygen intermediates (ROIs), an important part of their defense system. Oysters of the species Crassostrea virginica were held in normoxic (P(O)(2)=20.0-20.7 kPa, pH 7.8-8.0) and hypoxic conditions (P(O)(2)=4.0-6.7 kPa, pH 7.1-7.4). In vivo hemolymph variables (P(O)(2), P(CO)(2) and pH) were measured after both 1 hour and 2 days in each treatment to determine the appropriate environment for subsequent hemocyte experiments. Production of reactive oxygen intermediates by hemocytes was measured using luminol-enhanced chemiluminescence (CL). During CL tests, hemocytes were held under the following conditions: air (P(O)(2)=20.7, P(CO)(2)<0.07, pH 7.6), in vivo hemolymph conditions of normoxic oysters (P(O)(2)=5.2, P(CO)(2)=0.27, pH 7.6), and in vivo hemolymph conditions of hypoxic oysters (P(O)(2)=1.47, P(CO)(2)=0.53, pH 7.1). Production of ROIs under hypoxic conditions was 33 % of that under normoxia. This decrease was the result of specific and independent effects of lower oxygen levels and decreased pH. It was not due to any direct effect of CO(2).
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Affiliation(s)
- JN Boyd
- Grice Marine Laboratory, University of Charleston, Charleston, South Carolina 29412, USA.
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Dwyer Iii JJ, Burnett LE. Acid-Base Status of the Oyster Crassostrea virginica in Response to Air Exposure and to Infections by Perkinsus marinus. Biol Bull 1996; 190:139-147. [PMID: 29244552 DOI: 10.2307/1542682] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Hemolymph acid-base variables were investigated in the Eastern oyster, Crassostrea virginica, to determine its responses to air exposure and to infections by the parasite Perkinsus marinus. Infected and uninfected oysters were subjected to two treatments of temperature (21° and 30°C) and air exposure (5 and 24 h). Upon exposure to air, oysters underwent a respiratory acidosis that remained uncompensated in uninfected oysters but was partially compensated in highly infected oysters at both 21° and 30°C. The acidosis was significantly greater in oysters with high infections. Hemolymph in uninfected oysters had a greater buffering capacity (-6.80 +/- 0.76 SEM slykes) than hemolymph in highly infected oysters (-3.30 +/- 0.50 SEM slykes). Calcium ion concentrations in hemolymph increase when the hemolymph becomes acidic, suggesting that shell decalcification plays a role in buffering the acid. During air exposure, although oysters do not visibly gape, they access air and are apparently not completely anaerobic.
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Burnett LE, McMahon BR. Facilitation of CO2 excretion by carbonic anhydrase located on the surface of the basal membrane of crab gill epithelium. Respir Physiol 1985; 62:341-8. [PMID: 2418476 DOI: 10.1016/0034-5687(85)90089-1] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
An isolated perfused crab gill preparation was used to test the hypotheses that crab gill carbonic anhydrase (CA) catalyzes the efflux of CO2 from the hemolymph, which lacks the enzyme, to the ambient medium and that the CA is localized on the luminal surface of the basal membrane. It was found that the efflux of CO2 from the internal perfusate was sensitive to the flow rate of the internal perfusate through the gill (and thus the residence time within the gill). The sensitivity of the CO2 efflux to residence time was nearly abolished upon treatment of the gill with an impermeable dextran-bound CA inhibitor. It is concluded that CA present on the luminal surface of the gill epithelium facilitates CO2 excretion by catalyzing the dehydration of the large hemolymph bicarbonate pool to the more diffusible molecular CO. The action of the enzyme is important in maintaining a CO2 gradient between hemolymph and water in a situation where hemolymph PCO2 is normally low, water PCO2 is variable, and the gills themselves are a source of metabolic CO2.
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