Nitric oxide up-regulates ferritin mRNA level in snail neurons

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

Identification and characterization of a ferritin gene involved in the immune defense response of scallop Chlamys farreri

Scallop Chlamys farreri is an important aquaculture species in northern China. However, its mass mortality caused by several pathogens can result in great economic loss and negative impacts to the sustainable development of the scallop industry. Thus, improving the overall understanding of immune response mechanisms involved in host-pathogen interactions is necessary. Ferritins are conserved molecules in organisms that are involved in diverse biological processes, such as mediating host-pathogen responses. In this study, we report a novel ferritin gene from C. farreri (denoted as CfFER). The full length of CfFER is 848 bp and contains a 5'-UTR of 113 bp, a 3'-UTR of 219 bp, and a complete open reading frame (ORF) of 516 bp. The ORF encodes a polypeptide of 171 amino acid residues with a molecular weight of approximately 19.95 kDa and an isoelectric point of 5.07. The CfFER protein exhibited typical ferritin structures, namely, a ferroxidase diiron center, a ferrihydrite nucleation center, and an iron-binding response signature. Phylogenetic analysis revealed that CfFER was closely related to other mollusk ferritin proteins. Expression of CfFER in different tissues was analyzed by quantitative real-time PCR, and results showed that CfFER was ubiquitously expressed in all examined tissues. The highest and lowest expression levels of CfFER were measured in the muscle and hemocyte, respectively. The relative mRNA expression of CfFER in response to bacterial (Vibrio anguillarum) and viral (acute viral necrobiotic virus) challenges sharply increased by ca. 5-fold about12 h post-infection (hpi) and then normalized at 48 hpi. Western blot analysis with polyclonal antibodies generated from the recombinant product of CfFER also demonstrated the presence of ferritin protein in hemocytes. These findings strongly suggest that CfFER is involved in the immune response of C. farreri and protection against pathogen challenge.

Identification and characterization of four ferritin subunits involved in immune defense of the Yesso scallop (Patinopecten yessoensis)

As a primary iron storage protein, ferritin plays a vital role in iron homeostasis and innate immunity. In this study, four ferritin subunits (PyFer1, PyFer2, PyFer3, and PyFer4) were cloned from the Yesso scallop, Patinopecten yessoensis, by rapid amplification of cDNA ends (RACE) following in silico transcriptome analysis. The full-length cDNAs of the four ferritins are 895, 920, 891, and 1400 bp in length, respectively, and each contains a putative iron response element (IRE) in its 5' UTR. Meanwhile, multiple A+U-destabilizing elements (TATT or ATTTA) are present in the 3' UTRs of PyFer2 and PyFer4. The open reading frames of the four ferritins are 522, 516, 516, and 519 bp, encoding 173, 171, 171, and 172 amino acids, respectively. These proteins have typical ferritin structures, with four long α-helices, one short α-helix and an L-loop. All of the predicted proteins possess both the ferroxidase center of mammalian H ferritins (E25, Y32, E59, E60, H63, E105, and Q139) and the iron nucleation site of mammalian L ferritins (H116, D129, and E132), and the recombinant proteins possess apparent ferroxidase activity. Quantitative real-time PCR analysis revealed that the expression of the four PyFers was significantly elevated at the D-shaped stage and was relatively high in the adult mantle and hepatopancreas. Furthermore, the four PyFers were significantly up-regulated by iron or bacterial challenge, and all four purified recombinant PyFers were able to inhibit the growth of the scallop pathogen Vibrio anguillarum. These results suggest that these PyFers are likely to play important roles in many fundamental biological processes in P. yessoensis, including immune defense, iron homeostasis, and shell development.

Identification and characterization of a Tegillarca granosa ferritin regulated by iron ion exposure and thermal stress

Ferritin, a conserved iron storage protein of most living organisms, plays a crucial role in iron metabolism. In this study, the ferritin gene from Tegillarca granosa (denoted as TgFER) was identified by expressed sequence tag (EST) and PCR approaches. The full-length cDNA of TgFER was of 895bp, consisting of a 5'-UTR of 163 bp with a putative iron regulatory element (IRE), a 3'-UTR of 213 bp, and a complete open reading frame of 519 bp encoding a polypeptide with 172 amino acid residues. The predicted molecular mass of deduced amino acid of TgFER was 20.00 kDa and the theoretical pI was 4.89. The deduced amino acid of TgFER shared high identities to ferritin from abalone, oyster, clam and human. The tissue distribution of TgFER in the tissues of mantle, foot, gill, haemocytes and hepatopancreas was examined by quantitative real-time PCR (q-PCR) and mRNA transcripts of TgFER were found to be dominately expressed in haemocytes, hepatopancreas and gill and weakly in foot and mantle. The temporal expression of TgFER in haemocytes or hepatopancreases after challenged by metals ion (FeCl₂ and FeCl₃) exposure and thermal stress were also analyzed with q-PCR. The diverse expression patterns of TgFER were detected depending upon the types of stimulators and tissues. The ployconal antibodies generated from the recombinant product of TgFER could be specifically identified not only the recombinant product, but also the native protein from haemocytes. All these results strongly suggested that TgFER was involved in the iron metabolism and thermal stress regulation in T. granosa.

Identification and characterization of a clam ferritin from Sinonovacula constricta

Ferritin, a major iron storage protein of most living organisms, plays a crucial role in iron metabolism. Here we reported the isolation and characterization of a cDNA of ferritin gene from Sinonovacula constricta (denoted as ScFER). The full-length cDNA of ScFER was of 996 bp, consisting of a 5'-UTR of 120 bp, a 3'-UTR of 360 bp, and a complete open reading frame of 516 bp encoding a polypeptide with 171 amino acid residues. The predicted molecular mass of deduced amino acid of ScFER was 19.76 kDa and the theoretical pI was 5.07. Quantitative real-time PCR was employed to analyze the expression profiles of ScFER mRNA in muscle, mantle and visceral mass after iron exposure. The peak expression level of ScFER in the three tissues was 1.79-fold, 1.31-fold and 3.51-fold increases in muscle, mantle and visceral mass, respectively. The polyclonal antibodies generated from the recombinant product of ScFER could be specifically identified not only the recombinant product, but also the native protein from muscle. All these results strongly suggested that ScFER was involved in the iron metabolism regulation in S. constricta.

Two ferritin subunits from disk abalone (Haliotis discus discus): cloning, characterization and expression analysis

Ferritin plays a key role in cellular iron metabolism, which includes iron storage and detoxification. From disk abalone, Haliotis discus discus, the cDNA that encodes the two ferritin subunits abalone ferritin subunit 1 (Abf1) and abalone ferritin subunit 2 (Abf2) were cloned. The complete cDNA coding sequences for Abf1 and Abf2 contained 621 and 549 bp, encoding for 207 and 183 amino acid residues, respectively. The H. discus discus Abf2 subunit contained a highly conserved motif for the ferroxidase center, which consists of seven residues of a typical vertebrate heavy-chain ferritin with a typical stem-loop structure. Abf2 mRNA contains a 27 bp iron-responsive element (IRE) in the 5'UTR position. This IRE exhibited 96% similarity with pearl and Pacific oyster and 67% similarity with human H type IREs. However, the Abf1 subunit had neither ferroxidase center residues nor the IRE motif sequence; instead, it contained iron-binding region signature 2 (IBRS) residues. Recombinant Abf1 and Abf2 proteins were purified and the respective sizes were about 24 and 21 kDa. Abf1 and Abf2 exhibited iron-chelating activity 44.2% and 22.0%, respectively, at protein concentration of 6 microg/ml. Analysis of tissue-specific expression by RT-PCR revealed that Abf1 and Abf2 ferritin mRNAs were expressed in various abalone tissues, such as gill, mantle, gonad, foot and digestive tract in a wide distribution profile, but Abf2 expression was more prominent than Abf1.

Identification of genes involved in interactions between Biomphalaria glabrata and Schistosoma mansoni by suppression subtractive hybridization

Biomphalaria glabrata is an intermediate snail host for Schistosoma mansoni, a medically important schistosome. In order to identify transcripts involved in snail-schistosome interactions, subtractive cDNA libraries were prepared, using suppression subtractive hybridization (SSH) between a parasite-exposed schistosome-resistant and a susceptible strain of B. glabrata, and also between schistosome-exposed and unexposed snails from the resistant snail line. Separate libraries were made from both haemocytes and the haemopoietic organ. Subtraction was performed in both directions enriching for cDNAs differentially expressed between parasite-exposed resistant and susceptible samples and up or down-regulated in the resistant line after challenge. The resulting eight libraries were screened and eight genes, differentially expressed between the haemocytes of resistant and susceptible snail strains, were identified and confirmed with reverse transcriptase PCR, including two transcripts expected to be involved in the stress response mechanism for regulating the damaging oxidative burst pathways involved in cytotoxic killing of the parasite: the iron-storage and immunoregulatory molecule, ferritin, and HtrA2, a serine protease involved in the cellular stress response. Transcripts with elevated levels in the resistant strain, had the same expression patterns in the subtracted libraries and unsubtracted controls; higher levels in exposed resistant snails compared to susceptible ones and down-regulated in exposed compared with unexposed resistant snails. Differential expression of two of the transcripts with no known function from the susceptible strain, was independently confirmed in a repeat exposure experiment.

A cGMP-dependent cascade enhances an L-type-like Ca2+ current in identified snail neurons

We studied the impact of an NO-cGMP dependent signalling pathway on the high-voltage-activated (HVA) Ca(2+) current in identified neurons of the pulmonate snail, Helix pomatia, using Ba(2+) as charge carrier. The 3',5'-cyclic guanosine monophosphate (cGMP) analogues, dibutyryl-cGMP and 8-bromo-cGMP, consistently induced a biphasic response, consisting of an increase superseded by a decline of the Ba(2+) current. The NO donor, sodium nitroprusside (SNP), modulated only in a minority of neurons the Ba(2+) current. Blockade of protein kinase activity with 1-[5-isoquinolinesulfonyl]-2 methyl piperazine (H 7), a nonselective protein kinase inhibitor, or Rp-8-pCPT-cGMP, a selective protein kinase G (PKG) inhibitor, decreased, whereas Rp-cAMP, a selective protein kinase A (PKA) inhibitor, increased the Ba(2+) current upon application of cGMP analogues or SNP. Okadaic acid or calyculin, inhibitors of protein phosphatase 1 (PP1) and protein phosphatase 2A (PP2A), augmented the Ba(2+) current. Under these conditions, cGMP analogues or SNP had an additive-enhancing effect on the Ba(2+) current. When neurons were exposed to the nonselective phosphodiesterase (PDE) inhibitor 3-isobutyl-1-methylxanthine (IBMX), cGMP analogues induced a persistent increase of the Ba(2+) current, whereas SNP induced a biphasic response. These data suggest coexistence of cGMP-PKG and cGMP-PDE pathways as well as crosstalk between cGMP and 3',5'-cyclic adenosine monophosphate (cAMP) pathways, which converge on HVA Ca channels in Helix neurons. In this model, augmentation of the Ba(2+) current through HVA Ca channels is accomplished by PKA and PKG, whereas attenuation is mediated by PDEs, which prevent activation of protein kinases via hydrolysis of cyclic nucleotides.

Nitric Oxide Signaling in Plants

Plants have four nitric oxide synthase (NOS) enzymes. NOS1 appears mitochondrial, and inducible nitric oxide synthase (iNOS) chloroplastic. Distinct peroxisomal and apoplastic NOS enzymes are predicted. Nitrite-dependent NO synthesis is catalyzed by cytoplasmic nitrate reductase or a root plasma membrane enzyme, or occurs nonenzymatically. Nitric oxide undergoes both catalyzed and uncatalyzed oxidation. However, there is no evidence of reaction with superoxide, and S-nitrosylation reactions are unlikely except during hypoxia. The only proven direct targets of NO in plants are metalloenzymes and one metal complex. Nitric oxide inhibits apoplastic catalases/ascorbate peroxidases in some species but may stimulate these enzymes in others. Plants also have the NO response pathway involving cGMP, cADPR, and release of calcium from internal stores. Other known targets include chloroplast and mitochondrial electron transport. Nitric oxide suppresses Fenton chemistry by interacting with ferryl ion, preventing generation of hydroxyl radicals. Functions of NO in plant development, response to biotic and abiotic stressors, iron homeostasis, and regulation of respiration and photosynthesis may all be ascribed to interaction with one of these targets. Nitric oxide function in drought/abscisic acid (ABA)-induction of stomatal closure requires nitrate reductase and NOS1. Nitric oxide synthasel likely functions to produce sufficient NO to inhibit photosynthetic electron transport, allowing nitrite accumulation. Nitric oxide is produced during the hypersensitive response outside cells undergoing programmed cell death immediately prior to loss of plasma membrane integrity. A plasma membrane lipid-derived signal likely activates apoplastic NOS. Nitric oxide diffuses within the apoplast and signals neighboring cells via hydrogen peroxide (H2O2)-dependent induction of salicylic acid biosynthesis. Response to wounding appears to involve the same NOS and direct targets.

Nitric oxide inhibition decreases bleomycin-detectable iron in spleen, bone marrow cells and heart but not in liver in exercise rats

The possible role of nitric oxide on the exercise-induced changes in bleomycin-detectable iron (BDI) in the liver, spleen, bone marrow cells and heart was investigated. Female Sprague-Dawley rats were randomly assigned to four groups: S1 (Sedentary), S2 (Sedentary + L-NAME [N-nitro-L-arginine methyl ester]), E1 (Exercise) and E2 (Exercise + L-NAME). Animals in the E1 and E2 swam for 2 h/day for 3 months. L-NAME in the drinking water (1 mg/ml) was administrated to rats in the S2 and E2 groups for the same period. At the end of the 3rd month, nitrite and nitrate (NOx), BDI and non-heme iron (NHI) contents in the liver, spleen, bone marrow cells and heart were measured. The ratio of BDI/NHI was calculated. The exercise induced a significant increase in NOx and BDI contents and/or BDI/NHI ratio in the spleen, bone morrow cells and heart. Treatment with L-NAME, an inhibitor of NOS, led to a significant decrease in NOx and an increase in BDI levels and BDI/NHI ratios in these tissues. The correlative analysis showed that there is significantly positive correlation between NOx levels and BDI contents and/or BDI/NHI ratios in the spleen, bone marrow cells and heart. These results suggest that the increased nitric oxide might be one of the reasons leading to the increased BDI levels in these tissues in the exercised rats. In contrast to the above tissues, in the liver, exercise led to a significant decrease rather than increase in BDI levels and BDI/NHI ratios with a significant increase in NOx contents. Treatment with L-NAME led to a significant increase in BDI levels and BDI/NHI ratios and a decrease in NOx contents in the tissue. These findings plus the results reported by others imply that nitric oxide might have an inhibitory effect on BDI in the liver.

Crassostrea gigas ferritin: cDNA sequence analysis for two heavy chain type subunits and protein purification

Ferritin has been shown as being the principal iron storage in the majority of living organisms. In marine species, ferritin is also involved in high-level accumulation of (210)Po. As part of our work on the investigation of these radionuclides' concentration in natural environment, ferritin was searched at the gene and protein level. Ferritin was purified from the visceral mass of the oyster Crassostrea gigas by ion-exchange chromatography and HPLC. SDS-PAGE revealed one band of 20 kDa. An Expressed Sequence Tag (EST) library was screened and led to the identification of two complementary DNA (cDNA) involved in ferritin subunit expression. The complete coding sequences and the untranslated regions (UTRs) of the two genes were obtained and a 5' Rapid Amplification of cDNA Ends (RACE) was used to obtain the two iron-responsive elements (IREs) with the predicted stem-loop structures usually present in the 5'-UTR of ferritin mRNA. Sequence alignment in amino acid of the two new cDNA showed an identity with Pinctada fucata (85.4-88.3%), Lymnaea stagnalis (79.3-82.2%) and Helix pomatia (79.1-79.1%). The residues responsible for the ferroxidase center, conserved in all vertebrate H-ferritins, are present in the two oyster ferritin subunits. Oyster ferritins do not present the special characteristics of other invertebrate ferritins like insect ferritins but have some functional similarities with the vertebrate H chains ferritin.

Accumulation and translation of ferritin heavy chain transcripts following anoxia exposure in a marine invertebrate

Differential screening of a Littorina littorea (the common periwinkle) cDNA library identified ferritin heavy chain as an anoxia-induced gene in hepatopancreas. Northern blots showed that ferritin heavy chain transcript levels were elevated twofold during anoxia exposure, although nuclear run-off assays demonstrated that ferritin heavy chain mRNAs were not transcriptionally upregulated during anoxia. Polysome analysis indicated that existing ferritin transcripts were actively translated during the anoxic period. This result was confirmed via western blotting, which demonstrated a twofold increase in ferritin heavy chain protein levels during anoxia, with a subsequent decrease to control levels during normoxic recovery. Organ culture experiments using hepatopancreas slices demonstrated a >50% increase in ferritin heavy chain transcript levels in vitro under conditions of anoxia and freezing, as well as after incubation with the second messenger cGMP. Taken together, these results suggest that ferritin heavy chain is actively regulated during anoxia exposure in the marine snail, L. littorea.

Nitric oxide synthase and soluble guanylyl cyclase underlying the modulation of electrical oscillations in a central olfactory organ

We have isolated and characterized the cDNAs for nitric oxide synthase (NOS) and soluble guanylyl cyclase (sGC) from the terrestrial slug Limax marginatus, and examined the presence and distribution of their mRNAs in the central nervous system using histological techniques and a reverse transcription-polymerase chain reaction method. Our results showed that both bursting and nonbursting neurons in the procerebral lobes contain the mRNAs for both NOS and sGC. We further found that the oscillation frequency of electrical activity in the procerebral lobes increases with increasing intracellular concentrations of cyclic GMP (cGMP). Taken together with previous data on the NO-induced cGMP-like immunoreactivity and on the anatomical distribution of neurites and the localization of synapses of bursting and nonbursting neurons, our present results suggest that NO-induced changes in cGMP concentration modulate the oscillation frequency in the procerebral lobes by acting on the olfactory input pathways, but possibly not on the output pathways, in slugs. .