Combined effects of nano-TiO2 and hexavalent chromium towards marine crustacean Artemia salina

There has been a significant increased concern of the impact of the toxicity of multiple contaminants in the marine environment. Thus, this study was aimed at determining whether the interaction between nano-TiO₂ and Cr(VI) would modulate their toxic effects with the marine crustacean, Artemia salina. Nano-TiO₂ agglomerated in artificial sea water (ASW) and readily formed micron-sized particles that settled down in the medium. The addition of Cr(VI) to nano-TiO₂ aggravated their agglomeration through sorption of Cr(VI) onto nano-TiO₂. This was reflected by a decrease in the residual concentration of Cr in the suspension. Acute toxicity tests performed using pristine nano-TiO₂ (0.25, 0.5, 1, 2, and 4 mg/L) and Cr(VI) (0.125, 0.25, 0.5, and 1 mg/L) displayed a concentration dependent rise in the mortality of Artemia salina. To examine the effects of mixtures of nano-TiO₂ and Cr(VI) on Artemia salina, two groups of experiments were designed. The former group studied the toxic effect of nano-TiO₂ (0.5, 1, 2, and 4 mg/L) with a fixed concentration (0.125 mg/L) of Cr(VI). While the latter group studied the toxicity of Cr(VI) (0.25, 0.5, and 1 mg/L) with a fixed concentration (0.25 mg/L) of nano-TiO₂. The toxic effects of nano-TiO₂ was not significantly reduced at a fixed concentration of Cr(VI) but in contrast, a significant reduction in the Cr(VI) toxicity by fixed concentration of nano-TiO₂ was observed. Toxicity data was well supported by an independent action model that proved the mode of action between nano-TiO₂ and Cr(VI) to be antagonistic. Furthermore, ROS generation and measurement of antioxidant enzyme activities were also in line with toxicity results. From this study, the modification of Cr(VI) toxicity at fixed concentration of nano-TiO₂ could have a huge impact on the reduction in Cr(VI) toxicity across trophic levels.

Comparative analysis of two brine shrimps revealed differential expression pattern and functional characterization of CK2α under bacterial stimulation from different geographical distribution

Understanding how the brine shrimp responds to different geographical populations can provide novel insights on response to bacterial stimulation. In the paper, Artemia sinica from lower altitudes and Artemia parthenogenetica from higher altitudes of the Tibetan Plateau, were used to illustrate different defense against bacteria mechanisms that these organisms used to adapt to different geographical environments. Protein kinase CK2 is a serine/threonine kinase with a multitude of protein substrates. It is a ubiquitous enzyme essential for the viability of eukaryotic cells, where its functions in a variety of cellular processes, including cell cycle progression, apoptosis, transcription, and viral infection. The gene encodes the same mRNA sequence in A. sinica and A. parthenogenetica, named AsCK2α and ApCK2α, respectively. The open reading frame was obtained, a 1047-bp sequence encoding a predicted protein of 349 amino acids. To systematically analyze the expression of AsCK2α and ApCK2α during embryonic development and bacterial challenge, real-time PCR, Western blotting and immunohistochemistry were performed. The results showed that AsCK2α was higher than ApCK2α at different developmental stages. Under bacterial challenge, the expression of ApCK2α was significantly higher than AsCK2α. Protein localization analysis showed that AsCK2α and ApCK2α were mainly distributed in the head and chest. Our research revealed that CK2α plays a vital role in the growth, development and bacterial stimulation of the brine shrimp.

On the structural possibility of pore-forming mitochondrial FoF1 ATP synthase

The mitochondrial permeability transition is an inner mitochondrial membrane event involving the opening of the permeability transition pore concomitant with a sudden efflux of matrix solutes and breakdown of membrane potential. The mitochondrial F(o)F(1) ATP synthase has been proposed as the molecular identity of the permeability transition pore. The likeliness of potential pore-forming sites in the mitochondrial F(o)F(1) ATP synthase is discussed and a new model, the death finger model, is described. In this model, movement of a p-side density that connects the lipid-plug of the c-ring with the distal membrane bending Fo domain allows reversible opening of the c-ring and structural cross-talk with OSCP and the catalytic (αβ)(3) hexamer. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

A test for adequate wastewater treatment based on glutathione S transferase isoenzyme profile

Discharge to the environment of treated or non-treated municipal wastewater imposes several threats to coastal and estuarine ecosystems which are difficult to assess. In our study we evaluate the use of the isoenzyme profile of glutathione S transferase (GST) in combination with the kinetic characteristics of the whole enzyme and of heme peroxidase, as a test of adequate treatment of municipal wastewater. For this reason, Artemia nauplii were incubated in artificial seawater prepared by wastewater samples, such as secondary municipal effluents produced by a conventional activated sludge unit and advanced treated effluents produced by the employment of coagulation, activated carbon adsorption and chlorination as single processes or as combined ones. Characteristic changes of the isoenzyme pattern and the enzymes' kinetic properties were caused by chlorinated secondary municipal effluent or by secondary non-chlorinated effluent. Advanced treatment by combination of coagulation and/or carbon adsorption resulted to less prominent changes, suggesting more adequate treatment. Our results suggest that GST isoenzyme profile in combination with the kinetic properties of the total enzyme family is a sensitive test for the evaluation of the adequateness of the treatment of reclaimed wastewater and the reduction of potentially harmful compounds. Potentially, it may offer a 'fingerprint' characteristic of a particular effluent and probably of the treatment level it has been subjected.

Deubiquitinating enzyme BAP1 is involved in the formation and maintenance of the diapause embryos of Artemia

The modification of proteins by ubiquitination and deubiquitination plays an important role in various cellular processes. BRCA1-associated protein-1 (BAP1) is a deubiquitinating enzyme whose function in the control of the cell cycle requires both its deubiquitinating activity and nuclear localization. In the present study, a ubiquitin carboxyl-terminal hydrolase belonging to the BAP1 family was identified and characterized from Artemia parthenogenetica, a member of a family of brine shrimp that, under certain conditions, produce and release diapause embryos in which cell division and turnover of macromolecules are arrested. Western blot analysis and in vitro enzyme activity assay revealed ArBAP1 to be a cytoplasmic protein with typical ubiquitin hydrolase activity. Northern blot analysis revealed that ArBAP1 was abundant in the abdomen of Artemia producing diapause-destined embryos. Furthermore, by in situ hybridization, ArBAP1 was located exclusively in the embryos. In vivo knockdown of ArBAP1 by RNA interference resulted in the formation of embryos with split shells and abortive nauplii. The present findings suggest that ArBAP1, the first reported cytoplasmic BAP1, participates in the formation of diapause embryos and plays an important role in the control of cell cycle arrest in these encysted embryos.

Involvement of polo-like kinase 1 (Plk1) in mitotic arrest by inhibition of mitogen-activated protein kinase-extracellular signal-regulated kinase-ribosomal S6 kinase 1 (MEK-ERK-RSK1) cascade

Cell division is controlled through cooperation of different kinases. Of these, polo-like kinase 1 (Plk1) and p90 ribosomal S6 kinase 1 (RSK1) play key roles. Plk1 acts as a G(2)/M trigger, and RSK1 promotes G(1) progression. Although previous reports show that Plk1 is suppressed by RSK1 during meiosis in Xenopus oocytes, it is still not clear whether this is the case during mitosis or whether Plk1 counteracts the effects of RSK1. Few animal models are available for the study of controlled and transient cell cycle arrest. Here we show that encysted embryos (cysts) of the primitive crustacean Artemia are ideal for such research because they undergo complete cell cycle arrest when they enter diapause (a state of obligate dormancy). We found that Plk1 suppressed the activity of RSK1 during embryonic mitosis and that Plk1 was inhibited during embryonic diapause and mitotic arrest. In addition, studies on HeLa cells using Plk1 siRNA interference and overexpression showed that phosphorylation of RSK1 increased upon interference and decreased after overexpression, suggesting that Plk1 inhibits RSK1. Taken together, these findings provide insights into the regulation of Plk1 during cell division and Artemia diapause cyst formation and the correlation between the activity of Plk1 and RSK1.

Involvement of cyclin K posttranscriptional regulation in the formation of Artemia diapause cysts

Background

Artemia eggs tend to develop ovoviviparously to yield nauplius larvae in good rearing conditions; while under adverse situations, they tend to develop oviparously and encysted diapause embryos are formed instead. However, the intrinsic mechanisms regulating this process are not well understood.

Principal Finding

This study has characterized the function of cyclin K, a regulatory subunit of the positive transcription elongation factor b (P-TEFb) in the two different developmental pathways of Artemia. In the diapause-destined embryo, Western blots showed that the cyclin K protein was down-regulated as the embryo entered dormancy and reverted to relatively high levels of expression once development resumed, consistent with the fluctuations in phosphorylation of position 2 serines (Ser2) in the C-terminal domain (CTD) of the largest subunit (Rpb1) of RNA polymerase II (RNAP II). Interestingly, the cyclin K transcript levels remained constant during this process. In vitro translation data indicated that the template activity of cyclin K mRNA stored in the postdiapause cyst was repressed. In addition, in vivo knockdown of cyclin K in developing embryos by RNA interference eliminated phosphorylation of the CTD Ser2 of RNAP II and induced apoptosis by inhibiting the extracellular signal-regulated kinase (ERK) survival signaling pathway.

Conclusions/Significance

Taken together, these findings reveal a role for cyclin K in regulating RNAP II activity during diapause embryo development, which involves the post-transcriptional regulation of cyclin K. In addition, a further role was identified for cyclin K in regulating the control of cell survival during embryogenesis through ERK signaling pathways.

A prophenoloxidase from Artemia sinica: cDNA cloning, expression and activity analysis during early development

To understand the defense mechanisms of Crustacean animals, brine shrimp Artemia sinica prophenoloxidase (AsproPO) cDNA was cloned and its expression at early developmental stages was examined by reverse-transcription PCR (RT-PCR) and semi-quantitative RT-PCR, and activity of phenoloxidase (PO) at different developmental stages was further detected by using l-3,4-dihydroxyphenylalanine (l-DOPA) as a specific substrate in this study. It was found that the full-length of AsproPO cDNA is 2125 bp and it contains an open reading frame of 2100 bp encoding a protein of 699 amino acids. The deduced amino acid sequence of AsproPO has two putative copper binding sites highly conserved in Arthropods. Semi-quantitative RT-PCR analyses showed that the gene of AsproPO expressed at Emergence, Instar I and Instar II stages but did not at 0 h and 6 h stages. Activity measurement showed that PO activity could only be detected at Instar II stage but the other measured stages. All these implied that Artemia proPO immune system was complexly modulated during early development.

Purification and characterization of phenoloxidase from brine shrimp Artemia sinica

Phenoloxidase from Artemia sinica (AsPO) was purified by Superdex 200 gel-filtration and Q Sepharose fast flow ion-exchange chromatography, and its properties were characterized biochemically and enzymatically by using L-dihydroxyphenylalanine (L-DOPA) as the specific substrate. Results showed that AsPO was isolated as a monomeric protein of 125.5 kDa in molecular mass. The optimal pH value and temperature are 7.0 and 50°C, respectively, for its PO activity. The AsPO had an apparent K(m) value of 4.2 mM on L-DOPA, and 10.9 mM on catechol, respectively. Oxidase inhibitor on PO activity showed that the AsPO was extremely sensitive to ascorbic acid, sodium sulfite, and citric acid; and was very sensitive to cysteine, benzoic acid, and 1-phenyl-2-thiourea. Combined with its specific enzyme activity on L-DOPA and catechol, it can be concluded that AsPO is most probably a typical catechol-type O-diphenoloxidase. Its PO activity was also sensitive to metal ions and chelators, and 20 mM DETC-inhibited PO activity was obviously recovered by 15 mM Cu(2+), indicating that AsPO is most probably a copper-containing metalloenzyme. All these data about specific substrate, sensitivity to oxidase inhibitor metal ions and chelators indicate that the AsPO has the properties of a catechol-type copper-containing O-diphenoloxidase that functions as a vital humoral factor in host defense via melaninization as in other Crustaceans.

Alkaloids from stems of Esenbeckia leiocarpa Engl. (Rutaceae) as potential treatment for Alzheimer disease

Esenbeckia leiocarpa Engl. (Rutaceae), popularly known as guarantã, goiabeira, is a native tree from Brazil. Bioactivity-guided fractionation of the ethanol stems extract afforded the isolation of six alkaloids: leiokinine A, leptomerine, kokusaginine, skimmianine, maculine and flindersiamine. All isolated compounds were tested for acetyl cholinesterase inhibition, in vitro and displayed anticholinesterasic activity. The alkaloid leptomerine showed the highest activity (IC₅₀ = 2.5 mM), similar to that of the reference compound galanthamine (IC₅₀ = 1.7 mM). The results showed for the first time the presence of alkaloids leptomerine and skimmianine in E. leiocarpa (Engl.) with potent anticholinesterasic activity.

Expression and characterization of the JAK kinase and STAT protein from brine shrimp, Artemia franciscana

In this study, we isolated and characterized both JAK and STAT genes from Artemia, Artemia franciscana. Although AfJAK showed only 19% identity (33% similarity) to the Drosophila Hop protein, AfJAK contained the characteristic JAK homology domain (JH domain) from JH1 to JH7. On the other hand, AfSTAT showed higher identity (30%) to Drosophila STAT (STAT92E). The low identities of AfJAK and AfSTAT to Drosophila Hop and STAT92E suggest that JAK and STAT proteins are unique in each different species of invertebrate. RT-PCR analysis showed that both AfJAK and AfSTAT transcripts were ubiquitously expressed in the embryo, which is similar to the expression patterns of Drosophila Hop and STAT92E mRNAs during development. In addition, we generated a constitutively active form of AfSTAT by fusing the JH1 domain of AfJAK to the C-terminal end of AfSTAT. This fusion protein, AfSTAT-HA-JH1, autophosphorylated on its tyrosine residue and was able to bind to specific DNA motifs including the STAT-binding motifs in the Drosophila Raf promoter. Both AfJAK and AfSTAT proteins elicited the transactivation potential toward the fly Raf promoter in Sf9 cells. However, tyrosine phosphorylation of AfSTAT was not detected, which is consistent with the cellular localization analysis that most AfSTAT proteins were in the cytoplasm. Our results demonstrate that both JAK and STAT are present in the genome of Artemia, which can serve as the basis for further investigations to explore the role of the JAK/STAT signal pathway in the development and immune response of brine shrimp.

Purification and characterization of hatching enzyme from brine shrimp Artemia salina

By using Artemia chorion as a specific substrate, the hatching enzyme from Artemia salina (AHE) was purified by gel-filtration and ion-exchange chromatography, and characterized biochemically and enzymatically in this study. It was found that the AHE had a molecular weight of 82.2 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and often contained 73.3 kDa molecules in preparation. The AHE had obvious choriolytic activity, which was optimal at pH 7.0 and a temperature of 408C. The Km value of the AHE for dimethyl casein was 8.20 mg/ml. The AHE activity was almost completely inhibited by soybean trypsin inhibitor and p-amidinophenyl methane sulfonyl fluoride hydrochloride, greatly inhibited by N-tosyl-L-lysyl chloromethyl ketone, phenylmethanesulfonyl fluoride, and lima bean trypsin inhibitor, slightly inhibited by pepstatin, N-tosyl-L-phenylalanyl chloromethyl ketone, leupeptin, N-ethylmaleimide, and iodoacetamide, and not inhibited by chymostatin and bestatin. All these results imply that AHE is most probably a trypsin-type serine protease. Besides of these, AHE was also sensitive to EDTA and Zn21. Combined with the results that the EDTA-pre-treated HE activity could be perfectly recovered by Zn21, it is indicated that AHE might be also a kind of Zn-metalloprotease.

Development of digestive enzyme activity in larvae of spotted sand bass Paralabrax maculatofasciatus. 1. Biochemical analysis

Spotted sand bass Paralabrax maculatofasciatus is a potential aquaculture species in Northwest Mexico. In the last few years it has been possible to close its life cycle and to develop larviculture technology at on pilot scale using live food, however survival values are low (11%) and improvements in growth and survival requires the study of the morpho-physiological development during the initial ontogeny. In this research digestive activity of several enzymes were evaluated in larvae, from hatching to 30 days after hatching (dah), and in live prey (rotifers and Artemia), by use of biochemical and electrophoretic techniques. This paper, is the first of two parts, and covers only the biochemical analysis. All digestive enzyme activities were detected from mouth opening; however the, maximum activities varied among different digestive enzymes. For alkaline protease and trypsin the maximum activities were detected from 12 to 18 dah. Acid protease activity was observed from day 12 onwards. The other digestive enzymes appear between days 4 and 18 after hatching, with marked fluctuations. These activities indicate the beginning of the juvenile stage and the maturation of the digestive system, in agreement with changes that occur during morpho-physiological development and food changes from rotifers to Artemia. All enzymatic activities were detected in rotifers and Artemia, and their contribution to enhancement the digestion capacity of the larvae appears to be low, but cannot be minimised. We concluded that the enzymatic equipment of P. maculatofasciatus larvae is similar to that of other marine fish species, that it becomes complete between days 12 and 18 after hatching, and that it is totally efficient up to 25 dah.

The changes in the biochemical compositions and enzymatic activities of rotifer (Brachionus plicatilis, Müller) and Artemia during the enrichment and starvation periods

The changes in the biochemical compositions and enzymatic activities of rotifer (Brachionus plicatilis) and Artemia, enriched and stored at 4 degrees C temperature, were determined. The total starvation period was 16 h and samples were taken at the end of the 8th and 16th hours. In present study, the rotifer and nauplii catabolized a large proportion of the protein during the enrichment period. Lipid contents of both live preys increased during the enrichment period and decreased in nauplii and metanauplii throughout the starvation period but lipid content of the rotifer remained relatively constant during the starvation period. The changes observed in the amino acid compositions of Artemia and the rotifer were statistically significant (P < 0.05). The conspicuous decline the essential amino acid (EAA) and nonessential amino acid (NEAA) content of the rotifer was observed during the enrichment period. However, the essential amino acid (EAA) and nonessential amino acid (NEAA) contents of Artemia nauplii increased during the enrichment period. The unenriched and enriched rotifers contained more monounsaturated fatty acid (MUFAs) than polyunsaturated fatty acid (PUFAs) and saturated fatty acids (SFA). However, Artemia contained more PUFAs than MUFAs and SFA during the experimental period. A sharp increase in the amounts of docosahexaenoic acid (DHA) during the enrichment of the rotifer and Artemia nauplii was observed. However, the amount of DHA throughout the starvation period decreased in Artemia metanauplii but not in Artemia nauplii. Significant differences in tryptic, leucine aminopeptidase N (LAP), and alkaline phosphatase (AP) enzyme activities of Artemia and rotifer were observed during the enrichment and starvation period (P < 0.05). The digestive enzymes derived from live food to fish larvae provided the highest contribution at the end of the enrichment period. In conclusion, the results of the study provide important contributions to determine the most suitable live food offering time for marine fish larvae. Rotifer should be offered to fish larvae at the end of the enrichment period, Artemia nauplii just after hatching and before being stored at 4 degrees C, and Artemia metanauplii at the end of the enrichment and throughout the starvation period.

Energizing an Invertebrate Embryo: Bafilomycin‐Dependent Respiration and the Metabolic Cost of Proton Pumping by the V‐ATPase

We examine herein the contribution of V-ATPase activity to the energy budget of aerobically developing embryos of Artemia franciscana and discuss the results in the context of quiescence under anoxia. (31)P-NMR analysis indicates that intracellular pH and NTP levels are unaffected by acute incubation of dechorionated embryos with the V-ATPase inhibitor, bafilomycin A(1). Bafilomycin A(1) also has no significant effect on oxygen consumption by isolated mitochondria. Taken together, these data indicate that bafilomycin does not affect energy-producing pathways in the developing embryo. However, the V-ATPase inhibitor exhibits a concentration-dependent inhibition of oxygen consumption in aerobic embryos. A conservative analysis of respirometric data indicates that proton pumping by the V-ATPase, and processes immediately dependent on this activity, constitutes approximately 31% of the aerobic energy budget of the preemergent embryo. Given the complete absence of detectable Na(+)K(+)-ATPase activity during the first hours of aerobic development, it is plausible that the V-ATPase is performing a role in both the acidification of intracellular compartments and the energization of plasma membranes. Importantly, the high metabolic cost associated with maintaining these diverse proton gradients requires that V-ATPase activity be downregulated under anoxia in order to attain the almost complete metabolic depression observed in the quiescent embryo.

AMPK alpha subunit gene characterization in Artemia and expression during development and in response to stress

AMP-activated protein kinase (AMPK) plays a central role in maintaining the energy balance of organisms under physiological and environmental stresses. Here two AMPK alpha subunit gene transcripts (named Afr-AMPKalpha1 and Afr-AMPKalpha2) from Artemia franciscana were isolated and gene expression was characterized by semiquantitive reverse transcription-polymerase chain reaction (RT-PCR). Afr-AMPKalpha1 was differentially expressed during Artemia developmental stages as well as in response to stresses, such as heat-shock, starvation and a hyperosmotic environment. Afr-AMPKalpha1 mRNA expression in adult Artemia decreased under heat shock, but not in a time- and temperature-dependent manner. By contrast, the transcript sharply decreased in heat-shocked cysts in a time-dependent manner. Under hyperosmotic stress, however, the mRNA level in adults first declined and then increased with prolonged exposure. In the case of starvation, the gene expression in adults decreased and was undetectable after day 9. In addition, Afr-AMPKalpha2 mRNA expression was too low to be detected without nested PCR. Southern blot analysis, moreover, indicated AMPK alpha subunit was present in multiple copies in the Artemia genome. Furthermore, our results demonstrate that the Afr-AMPKalpha1 mRNA level sharply decreases in Artemia carrying diapause-destined embryos and this indicates the possibility that Afr-AMPKalpha1 is involved in determining the reproductive mode in Artemia.

Further characterization of the cathepsin L-associated protein and its gene in two species of the brine shrimp, Artemia

The major cysteine protease in embryos and larvae of the brine shrimp Artemia franciscana is a heterodimer composed of a cathepsin L-like polypeptide of 28.5 kDa and a 31.5 kDa polypeptide called the cathepsin L-associated protein or CLAP. In a previous study, CLAP was shown to be a cell adhesion protein containing two Fas I domains and two GTP/ATP binding sites known as Walker A and B motifs. Here, we have characterized CLAP and its genes to better understand the role of this protein in Artemia development. The polymerase chain reaction was used to investigate the structure of the CLAP gene in two species of Artemia, the New World bisexual diploid A. franciscana and the Old World parthenogenetic tetraploid Artemia parthenogenetica. The protein coding region of the CLAP gene from each species was 99.5% identical for a protein of 332 amino acids, while the 3' non-coding region, representing nearly 45% of the gene, was only 86% identical between the two related species. However, while the CLAP gene is intronless in A. franciscana, in A. parthenogenetica the gene contained a mini-intron of 30 base pairs in the 3' non-coding region. The sequences representing the CLAP gene in A. franciscana and A. parthenogenetica have been entered into the NCBI database as AY757920 and DQ100385, respectively. Northern blot analysis showed that while the cathepsin L gene is expressed constitutively in Artemia franciscana embryos and young larvae, the CLAP gene is not expressed in late embryos and young larvae. In contrast, Western blots indicated that CLAP is present in developing embryos and young larvae, at least to the first larval molt, supporting results obtained previously showing CLAP's resistance to degradation by its dimeric partner, cathepsin L. At the protein level we showed that the GTP/ATP binding sites in CLAP are functional with rate constants of 0.024 and 0.022 for GTP and ATP hydrolase activity, respectively. GTP but not ATP also had a slight stimulatory effect on cathepsin L activity of the heterodimeric protease containing CLAP. Our results support the hypothesis that CLAP plays an important role in targeting and expression regulation of cathepsin L activity during early development of Artemia.

Functional and phylogenetic analyses of phenoloxidases from brachyuran (Cancer magister) and branchiopod (Artemia franciscana, Triops longicaudatus) crustaceans

Arthropod phenoloxidases catalyze the melanization and sclerotization of the new postmolt exoskeleton, and they function in the immune response. Hemocyanin, phylogenetically related to phenoloxidase, can function as a phenoloxidase under certain conditions. We investigated the relative contributions of hemocyte phenoloxidase and hemocyanin in the brachyuran crab Cancer magister, using the physiological ratio at which they occur in the hemolymph, and found that hemocyte phenoloxidase has higher activity. They both convert diphenols to o-quinones, but only the hemocyte phenoloxidase is able to catalyze the conversion of monophenols to diphenols. The quaternary structure of hemocyanin affects its reactivity as phenoloxidase. We suggest that prophenoloxidase is released from hemocytes and moves across epidermis into new exoskeleton during premolt and is activated in early postmolt. In addition to functional studies, we have determined the complete cDNA sequence of C. magister hemocyte prophenoloxidase and partial sequences from the branchiopods Artemia franciscana and Triops longicaudatus. We also sequenced C. magister cryptocyanin 2 and a hemocyanin from the amphipod Cyamus scammoni and used these and other members of the arthropod hemocyanin superfamily for phylogenetic analyses. The phylogenies presented here are consistent with the possibility that a common ancestral molecule had both phenoloxidase and reversible oxygen-binding capabilities.

Characterization of a cathepsin L-associated protein in Artemia and its relationship to the FAS-I family of cell adhesion proteins

We reported previously that the major cysteine protease in embryos and larvae of the brine shrimp, Artemia franciscana, is a heterodimeric protein consisting of a catalytic subunit (28.5 kDa) with a high degree of homology with cathepsin L, and a noncatalytic subunit (31.5 kDa) of unknown function. In the study reported here the noncatalytic subunit, or cathepsin L-associated protein (CLAP), was separated from cathepsin L by chromatography on Mono S and found to contain multiple isoforms with pIs ranging from 5.9 to 6.1. Heterodimeric and monomeric cathepsin L showed similar activity between pH 5 and 6.5, while the heterodimer was about twice as active as monomeric cathepsin L below pH 5. The heterodimer was more stable than the monomer between pH 6 and 7.4 and at 30-50 degrees C. Artemia CLAP and cathepsin L are present in nearly equimolar amounts at all stages in the life cycle and most abundant in encysted eggs and embyros. Moreover, CLAP, either free or as a complex with cathepsin L, was resistant to hydrolysis by cathepsin L. Two clones coding for CLAP were isolated from an Artemia embryo cDNA library and sequenced. Both clones have nearly identical open reading frames, but show differences at the 5'- and 3'-termini. Each cDNA clone has an extensive 3'-untranslated region containing 70-72% A+T. The deduced amino acid sequence of CLAP cDNA revealed two domains which were very similar to domains in fasciclin I and other cell adhesion proteins. The nucleotide sequences of clones 1 and 2 have been entered into the NCBI database (AY307377 and AY462276). This study supports the view that the noncatalytic subunit of the heterodimeric cysteine protease in Artemia stabilizes cathepsin L at various pH and temperatures normally inconsistent with cathepsin L from other organisms, and that CLAP serves as a docking mechanism for cathepsin L at nonlysosomal sites in Artemia embryos.

[Immunocytochemical studies on the phase of differentiation of hatching gland cells in brine shrimp, Artemia salina]

Hatching enzyme (HE), synthesized in hatching gland cells (HGCs), plays vital roles in animal hatching. Immunocytochemical techniques employing anti-GST-UVS.2 antiserum, prepared from Xenopus HE and with specificity to brine shrimp HE, were first used to investigate the differentiation and variability of hatching gland cells (HGCs) in the hatching process of embryos of brine shrimp, Artemia salina, in this study. HGCs with immunoreactivity to anti-GST-UVS.2 antiserum were identified, for the first time, in brine shrimp embryos during hatching process. Immunocytochemical staining results showed that, (1) HE-positive immunoreactivity is really specific to Artemia HE, and its appearance and disappearance are closely correlated with the hatching process of Artemia salina. (2) Artemia HGCs, first appeared in embryos 5 hours before hatching and disappeared 4 hours after hatching, were also a transient type of cells, with an existence period of 9 hours. (3) The head portion of Artemia embryo is probably the initial position of HE secretion, and likely to be the main position of HE secretion as well. The detailed process and mechanism need to be studied. (4) The appearance of HGCs is in a synchronous mode from places all over the embryos, and their disappearance is also in a synchronous mode. (5) The number of HGCs increased gradually along with embryo development process and reached a maximum number at hatching. Contrarily, the number of HGCs decreased gradually after hatching, and HGCs disappeared 5 hours after hatching. However, the intensity of HE-positive reaction was almost at the same level at the period of HGCs'presence. (6) Artemia HGCs were distributed throughout the body of embryos at all time during their presence. Therefore, it can concluded that Artemia HGCs, as a transient type of cells, first appeared in embryos 4 hours before hatching and disappeared in embryos 5 hours after hatching, and with distinguished patterns of appearance, disappearance and distribution in embryos. What is the final destiny of Artemia HGCs after hatching? And what is the biological significance of remanet HGCs, still existing until 4 hours after hatching, in fresh-hatched Artemia larvae? Is it possible that the HGCs are involved in larvae yolk digestion? Moreover, what is the molecular mechanism of HGCs' synchronous sudden appearance and disappearance? All these questions remain to be further studied and approved.

A 49 kDa microtubule cross-linking protein from Artemia franciscana is a coenzyme A-transferase

Embryos and larvae of the brine shrimp, Artemia franciscana, were shown previously to possess a protein, now termed p49, which cross-links microtubules in vitro. Molecular characteristics of p49 were described, but the protein's identity and its role in the cell were not determined. Degenerate oligonucleotide primers designed on the basis of peptide sequence obtained by Edman degradation during this study were used to generate p49 cDNAs by RT-PCR and these were cloned and sequenced. Comparison with archived sequences revealed that the deduced amino acid sequence of p49 resembled the Drosophila gene product CG7920, as well as related proteins encoded in the genomes of Anopheles and Caenorhabditis. Similar proteins exist in several bacteria but no evident homologues were found in vertebrates and plants, and only very distant homologues resided in yeast. When evolutionary relationships were compared, p49 and the homologues from Drosophila, Anopheles and Caenorhabditis formed a distinct subcluster within phylogenetic trees. Additionally, the predicted secondary structures of p49, 4-hydroxybutyrate CoA-transferase from Clostridium aminobutyricum and glutaconate CoA-transferase from Acidaminococcus fermentans were similar and the enzymes may possess related catalytic mechanisms. The purified Artemia protein exhibited 4-hydroxybutyrate CoA-transferase activity, thereby establishing p49 as the first crustacean CoA-transferase to be characterized. Probing of Western blots with an antibody against p49 revealed a cross-reactive protein in Drosophila that associated with microtubules, but to a lesser extent than did p49 from Artemia.

The effects of a copper-based antifouling paint on mortality and enzymatic activity of a non-target marine organism

Antifouling paints are used on a wide range of underwater structures in order to protect them from the development of fouling organisms. The leaching of the toxic substances from the matrix of the paint causes toxic effects not only to the fouling organisms but also on other "non-target" biota. The present study addresses the impact of the antifouling paint Flexgard VI-II on brine shrimp nauplii selected as convenient test organisms. The surface to volume (S/V) concept developed by Persoone and Castritsi-Catharios (1989) was used to determine S/V-LC50s for the test biota exposed to PVC test panels of 400-1000 mm2 surface coated with the antifouling paint in test vessels containing 20 ml seawater. Total ATPase and Mg2+-ATPase were also analyzed for coated surface areas inducing less than 50% mortality in the brine shrimp nauplii. The calculated S/V-LC50 (24 h) was 24.6 mm2/ml, which shows the high toxic character of the antifouling paint. Decreased enzymatic activities were noted in the brine shrimp nauplii exposed to test panels of 50 and 100 mm2 in 20 ml seawater. The present study indicates that the "surface to volume" concept is an interesting methodology that can be applied with both lethal and sublethal effect criteria for the determination of toxic stress from leaches of painted surfaces.

A butyrylcholinesterase in the early development of the brine shrimp (Artemia salina) larvae: a target for phthalate ester embryotoxicity?

The phthalate ester insensitive blue-green algae (Synechococcus lividus) were used as a food source to extend the survival of synchronously hatched brine shrimp (Artemia salina) larvae allowing measurement of a reduced toxic response to phthalate esters at late post-hatching stages of development. The maximum acute toxicity due to di-n-butyl phthalate (DNBP) correlated with the expression of a phthalate ester-hydrolyzing enzyme. The purified enzyme was identified as a butyrylcholinesterase due to its rapid inactivation by low concentrations (10(-7)M) of diisopropyl fluorophosphate and inhibition by physostigmine (IC(50)=6 x 10(-7)M) and tetraisopropylpyrophosphoramide (I-OMPA, IC(50)=x 10(-6)M) but not by BW284c5. Apparently competition of the phthalates with the endogenous substrates of the enzyme led to development-dependent toxicity.

Characterisation of cholinesterases and evaluation of the inhibitory potential of chlorpyrifos and dichlorvos to Artemia salina and Artemia parthenogenetica

In this study, the acute toxicity of the organophosphorous pesticides dichlorvos and chlorpyrifos to two different species of Artemia (A. salina and A. parthenogenetica) was evaluated. In addition, the in vivo effect of these two pesticides on cholinesterase (ChE) activity of both A. salina and A. parthenogenetica was also determined. The characterisation of the ChE, using different substrates and specific inhibitors, and the normal range of activity in non-exposed individuals were previously investigated for both species. The results obtained indicate that the ChE of A. salina is different from that of A. parthenogenetica and that both enzymes cannot be classified neither as acetylcholinesterase nor as butyrylcholinesterase since they show intermediary characteristics between the two vertebrate forms. The range of normal ChE activity was 2.65+/-0.15 U/mg protein for A. salina, and 3.69+/-0.17 U/mg protein for A. parthenogenetica. Significant in vivo effects of both pesticides on Artemia ChE activity were found, at concentrations between 5.38 and 9.30 mg/l for dichlorvos and between 1.85 and 3.19 mg/l for chlorpyrifos. Both Artemia species are resistant to these pesticides and they are able to survive with more than 80% ChE inhibition. However, A. parthenogenetica is more resistant than A. salina, with about a 95% reduction in its ChE activity respect to the control for nauplii exposed to the median lethal concentrations (LC50), without lethal effects after 24 h of exposure.

Surfactant-based oil dispersant toxicity to developing nauplii of Artemia: effects on ATPase enzymatic system

The paper deals with the toxicity of a surfactant-based oil dispersant to the ATPase activities of two naupliar stages of Artemia (instar I & II). Both instars were exposed to sub-lethal and lethal concentrations derived from acute toxicity data. The chosen concentrations were near to LOECs and NOECs. An eightfold difference indicated between the instars was instar-exposure time dependent. The most prominent effects were the inhibition and the stimulation of Na+/K+-ATPase and Mg2+-ATPase activities, respectively. The cause of these effects was related to the dispersant components, the surfactants. The pattern stimulation/inhibition of Mg2+-ATPase and Na+/K+-ATPase activities could be used to indicate toxic stress by surfactant-based oil dispersants since previous studies with other contaminants have shown different ATPase activity patterns.

Identification of the S6 kinase activity stimulated in quiescent brine shrimp embryos upon entry to preemergence development as p70 ribosomal protein S6 kinase: isolation of Artemia franciscana p70S6k cDNA

We previously demonstrated that a protein kinase responsible for phosphorylating 40S ribosomal subunits is activated in quiescent Artemia franciscana embryos within 15 min of restoration of normal tonicity and incubation at 30 degrees C. Here, we identify the activated S6 kinase as A. franciscana p70 ribosomal S6 kinase (p70S6k) subsequent to the isolation of an Artemia p70S6k cDNA. The protein conceptually translated from cDNA has 70% similarity and 64% identity to both Drosophila melanogaster and human p70S6k. Southern blot analysis is consistent with presence of a single p70S6k gene. Two transcripts of 5.4 and 2.7 kb were found. Abundance of both mRNAs increased dramatically around 4 h of preemergence development, and exhibited different steady-state level variation thereafter. Stimulated S6 kinase activity, partially purified by Superose 6 chromatography, correlated best with the slowest migrating, approximately 65 kDa, form detected by Western analysis using a specific polyclonal antibody made to a peptide from the predicted p70S6k NH2-terminus. Furthermore, the A. franciscana p70S6k was immunoprecipitated with the same antibody, showing in parallel an S6 kinase activity similar to peak profiles. We conclude that the stimulated S6 kinase activity is that of an ortholog of human p70S6k that may be involved in the regulation of protein synthesis during preemergence development in A. franciscana species.

Use of ribonuclease VI from Artemia for the determination of cytidine 2'-phosphate

An enzymatic method has been developed for the quantitative measurement of cytidine 2'-phosphate. Concentrations in the micromolar range can be measured even in the presence of at least five times greater concentrations of a variety of related nucleotides. The method is also suitable for detection of the 2',3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) and its discrimination from the 2',3'-cyclic nucleotide 2'-phosphodiesterase (EC 3.1.4.16).

Identification of a mitochondrial RNA polymerase in the crustacean Artemia franciscana

Mitochondrial RNA polymerase activity has been isolated from the crustacean Artemia franciscana at two stages of development, dormant embryo and developing larva. The preparations were obtained from purified mitochondria and the polymerase activity was purified by heparin-Sepharose chromatography. The presumed polymerase has a molecular mass of about 120 kDa and a 7.4 S sedimentation coefficient. The biochemical characterization of the enzymatic reaction identified our RNA polymerase preparations as mitochondrial. The transcription initiation sites of Artemia mtDNA were characterized recently in our laboratory (J. A. Carrodeguas and C. G. Vallejo, Eur. J. Biochem. 250, 514-523, 1997). Artemia mtDNA fragments comprising the transcription initiation sites were transcribed by the partially purified polymerase preparation from the two developmental stages, but the transcription turned out to be unspecific. DNAse I footprinting analysis of a main transcription initiation site-containing DNA fragment revealed a protected region around the initiation site +1 position, when using a crude polymerase preparation. However, the protected region was not observed with the purified preparation. The results altogether suggest that a specificity factor is lost during purification. Based on the footprinting data, we suggest that the sequence from positions -6 to +13 of the main transcription initiation site in the Artemia mitochondrial DNA is the binding site of the homologous RNA polymerase holoenzyme.

Gene expression of trehalase during post-dormant development of the brine shrimp, Artemia: comparison of the two species

Based on a homology screening approach, two degenerate oligonucleotides were employed as primers in a polymerase chain reaction to amplify a fragment of DNA encoding trehalase with a template of cDNA derived from embryos of American Artemia. Sequence analysis revealed that the fragment was composed of 228 bp comprising 76 amino acids, and highly homologous to trehalases of Tenebrio molitor (mealworm beetle), rabbit, Caenorhabditis elegans, Bombyx mori (silkworm) and Escherichia coli treA and treF (58-38%, in order of description). This fragment was used as a hybridization probe. A Northern blot analysis on American Artemia showed three transcripts of 5.0, 2.7 and 2.2 kb, and the two larger transcripts were also detected in Chinese Artemia. The developmental profile of the gene expression and the trehalase activity suggest that the transcripts of 5.0 and (or) 2.7 kb in both Artemia may be directly or indirectly related to translation of the trehalase. A Southern blot analysis on both Artemia suggested the existence of two highly homologous genes or one gene having an intron within the region where the probe binds in their haploid genome.

Protein kinases in mitochondria of the invertebrate Artemia franciscana

The information concerning protein kinases in animal mitochondria is scarce and related only to mammals. No data are available for invertebrates. We demonstrate here the presence of casein kinase II (CK II) and cAMP-dependent protein kinase (PKA) in the purified mitochondria of the crustacean Artemia franciscana. Whereas the mitochondrial CK II showed the same characteristics of the cytosolic enzyme, mitochondrial PKA had an apparent Km for its substrate Kemptide 1 order of magnitude lower than that of the cytosolic enzyme. CK II and PKA phosphorylate different sets of proteins in Artemia mitochondria in vitro. The use of an activity gel assay has allowed the detection of additional protein kinases, as yet unidentified, in Artemia mitochondria.

Polymorphism and structure of the gene coding for the alpha 1 subunit of the Artemia franciscana Na/K-ATPase

Genomic clones coding for one of the two identified Artemia franciscana Na/K-ATPase alpha subunits, the alpha 1 subunit, have been isolated. Several overlapping clones were obtained, although their restriction maps showed a large heterogeneity. Sequencing of their exons showed that they differ in up to 3.46% of their nucleotides in translated regions and 8.18% in untranslated regions. Southern blot analysis of DNA purified from different lots of A. franciscana cysts and from isolated individuals suggests that the variation is due to the existence of multiple Na/K-ATPase alpha 1 subunit alleles in A. franciscana. The Na/K-ATPase alpha 1 subunit gene is divided into 15 exons. Ten of the 14 introns are located in identical positions in this gene as in the human Na/K-ATPase alpha 3 subunit gene. Analysis of the 5' flanking region of the gene has allowed identification of the transcription-initiation sites. The adjacent upstream region has been shown to have functional promoter activity in cultured mammalian cells, suggesting the evolutionary conservation of some of the promoter regulatory sequences.

Effect of demethylation on the chitinase inhibitory activity of allosamidin

Removal of a methyl group of the allosamizoline moiety of allosamidin decreases the inhibitory effect on family 18 chitinases from three different species (a bacterium, Serratia marcescens, a crustacean, Artemia salina, and an insect cell line, Chironomus tentans). Loss of a second methyl group weakens enzyme inhibition further. This is in agreement with the highly conserved catalytic centre of these enzymes.

Purification and characterization of Artemia 2',3'-cyclic nucleotide 3'-phosphodiesterase

This paper describes the purification and properties of a 2',3'-cyclic nucleotide 3'-phosphodiesterase which hydrolyzes nucleoside 2',3'-cyclic monophosphates to nucleoside 2'-phosphates. The enzyme is present in encysted gastrulae of Artemia and its specific activity greatly increases during larval development. The purified enzyme has a molecular weight of around 55 000 as estimated by gel filtration, does not require metals for activity, is inhibited by Zn2+ and inactivated by Cu2+ and has a pH optimum at around neutrality. Based on the relative values of V(max)/Km, the specificity of the phosphodiesterase toward the four 2',3'-cyclic nucleotides is Guo-2',3'-P > Ado-2',3'-P > Cyd-2',3'-P > Urd-2',3'-P = 45:36:20:7. The enzyme from Artemia gastrulae is competitively inhibited by the four nucleosides 2'-phosphates (Ki values around 1 mM) while the enzyme from larvae is only inhibited by the purine nucleotides. The phosphodiesterase characterized in this work is more similar in substrate specificity to the 2',3'-cyclic nucleotide 3'-phosphodiesterase from the mammalian nervous system than to the plant enzyme. The functional relationship of this enzyme with the Artemia ribonuclease VI is discussed.

Thermal stability of Artemia HGPRT: effect of substrates on inactivation kinetics

Hypoxanthine-guanine phosphoribosyltransferase (HGPRT, E.C.2.4.2.8) from Artemia cysts exhibits maximum activity at 70 degrees C. Its thermal stability has been examined following enzymatic activity as a function of temperature. Cold-induced renaturation experiments of samples heated at increasing temperatures showed that reversibility of thermal inactivation depends on the incubation time and final temperature. Prolonged incubation of the thermoinactivated enzyme at 0 degree C did not afford any further increase of the catalytic activity at 37 degrees C. The complex substrate PRPP:Mg protects HGPRT from thermal inactivation. However, incubations with hypoxanthine rendered a less thermostable enzyme at any temperature tested. The irreversible inactivation of HGPRT proceeds in two exponential steps. The analysis of the apparent rate constants for the fast and the slow phases, lambda 1 and lambda 2 as per the Lumry and Eyring model suggests the existence of more than three states in the thermal denaturation pathway of the free enzyme. In the presence of PRPP:Mg the irreversible process follows a single exponential and proceeds very slowly below 70 degrees C. PRPP:Mg also protects the enzyme from inactivation by NEM and pCMB, suggesting that -SH groups may be in the vicinity of the active site.

Specific ADP-ribose pyrophosphatase from Artemia cysts and rat liver: effects of nitroprusside, fluoride and ionic strength

One specific ADP-ribose pyrophosphatase (ADPRibase) has been identified in Artemia cysts, following a protocol that in rat liver allows the identification of three ADPRibases. Artemia ADPRibase resulted similar, but not identical, to rat liver ADPRibase-I with respect to known and novel properties disclosed in this work. In the presence of Mg2+, Artemia ADPRibase was highly specific for ADP-ribose and showed a low, 0.7 microM Km. Preincubation with the nitric oxide donor nitroprusside and dithiothreitol, elicited dose- and time-dependent, severalfold increase of Km and decrease of Vmax. At saturating ADP-ribose concentrations, fluoride was a strong inhibitor (IC50 approximately equal to 10-20 microM), whereas bringing ionic strength to 0.3-1.3 mol/l doubled the activity measured at lower or higher strengths. The novel fluoride and ionic strength effects were studied also with rat liver ADPRibase-I. Differences between the Artemia enzyme and ADPRibase-I concerned molecular weight (31,000 versus 38,500, respectively), Mn2+ ability to substitute for Mg2+ as the activating cation (better for the rat enzyme), and Vmax decrease by nitroprusside (not seen with the rat enzyme). The results are discussed in relation with the role of specific ADPRibases as protective factors limiting free ADP-ribose accumulation and protein glycation, and as targets for cytotoxic agents.

Tissue-specific expression of two Artemia franciscana sarco/endoplasmic reticulum Ca-ATPase isoforms

The sarco/endoplasmic reticulum Ca-ATPase (SERCA) gene from Artemia franciscana is transcribed into two mRNAs that code for two different enzyme isoforms. We investigated the tissue-specific expression of each mRNA by in situ hybridization of larval tissue sections. One of the isoforms is expressed in the muscle fibers of the appendages. The other isoform is generally expressed throughout all tissues of the larvae. The tissue distribution of these two isoforms is very similar to the one described for the two homologous isoforms generated from the vertebrate SERCA 2 gene, and shows the evolutionarily conserved nature of their tissue-specific expression.

Valyl-tRNA synthetase from Artemia. Purification and association with elongation factor 1

Two components of the protein biosynthetic machinery, valyl-transfer RNA synthetase (VRS) and elongation factor 1 (EF-1), have been isolated as a complex from several mammalian tissues. However, yeast VRS, which lacks an amino-terminal extension, does not associated with EF-1. We purified VRS from the brine shrimp Artemia and investigated its interaction with EF-1. Western blotting of crude Artemia extracts revealed the presence of two forms of VRS, differing in size and capacity to associate with EF-1. About 80% of the total VRS corresponds to a polypeptide of 130 kDa which behaves as a monomer upon gel filtration. Only the larger form of 140 kDa coelutes, cosediments and co-immunoprecipitates with the EF-1 alpha 2 beta gamma delta complex. The ratio of the two forms of VRS remains constant throughout early development. The possible origin and mode of expression of the two forms of VRS present in Artemia are discussed.

Potential role in development of the major cysteine protease in larvae of the brine shrimp Artemia franciscana

Encysted embryos and larvae of the brine shrimp Artemia franciscana contain a cysteine protease which represents over 90% of the protease activity in these organisms. We have used immunocytochemical methods to determine the localization and potential role of the cysteine protease in development of young larvae. In prenauplius larvae, there is intense staining for the protease on the basal side of the epidermal layer in the posterior region and diffuse staining for the protease throughout the embryo. In first instar larvae, cysteine-protease staining becomes intense in the midgut-forming area where a reticulum-like pattern emerges in cells with an abundance of yolk platelets. Cysteine-protease staining in second instar larvae becomes intense in the apical side of epidermal cells and in the basal and apical zones of midgut cells. Subcellular localization of the protease in the epidermis and midgut of young larvae using immunogold electron microscopy suggests that most is located in the cytosol and extracellular matrix adjacent to these cells. Addition of cysteine-protease inhibitors to the growth medium, especially the fluoromethyl ketone Z-Phe-Ala-CH2F, inhibits growth and segmentation of the thorax. Collectively, these observations suggest that the major cysteine protease in embryos and larvae functions in yolk utilization, as a hatching enzyme, in apolysis during the molt cycle, and as a digestive enzyme when the swimming larvae begin to feed.

Tissue-specific alternative promoters regulate the expression of the two sarco/endoplasmic reticulum Ca-ATPase isoforms from Artemia franciscana

The sarco/endoplasmic reticulum Ca-ATPase gene from Artemia franciscana is transcribed into two mRNAs of 4.5 and 5.2 kb that code for protein isoforms differing at their carboxyl terminus. Northern blot assays and anchored polymerase chain reaction (PCR) experiments have shown that these two mRNAs also differ at the initial part of their 5' untranslated region. The 5.2-kb mRNA-specific 5' untranslated region is present as an independent exon whose transcription is regulated by a promoter different from the one previously described that regulates the expression of the 4.5-kb mRNA. The nucleotide sequence of the 5.2-kb mRNA promoter and the transcription initiation site have been determined. These results suggest that the expression of the two protein isoforms is regulated in A. franciscana at the transcription initiation step, in contrast with the vertebrates sarco/endoplasmic reticulum Ca-ATPase genes 1 and 2 which have unique promoters for transcription of the two isoforms encoded by each gene.

In situ hybridization analyses of Na, K-ATPase alpha-subunit expression during early larval development of Artemia franciscana

The spatial pattern of expression of the mRNA encoded by the Na,K-ATPase alpha-subunit cDNA clone pArATNa136 was determined by in situ hybridization of first, second, and third instar Artemia franciscana larvae. This mRNA was expressed at high levels in the salt gland, the antennal gland, and the end of the midgut, which are the three main osmoregulatory organs in Artemia at these stages of development. The pattern of expression was similar at the three stages of development analyzed, although the level of expression increased during development, especially in the salt and antennal glands. The expression of the mRNA coding for another Na, K-ATPase alpha-subunit isoform, the proposed alpha 2-isoform, was also determined and was shown to be limited to the salt gland. These results suggest that the clone pArATNa136 codes for the biochemically defined alpha 1-isoform of the Na,K-ATPase alpha-subunit and reinforce the importance of this isoform in osmoregulation at the three larval stages studied. The alpha 2-isoform may also be involved in osmoregulation during the first stages of larval development.

Structure of Artemia franciscana sarco/endoplasmic reticulum Ca-ATPase gene

Genomic clones coding for the Artemia franciscana sarco(endo)plasmic reticulum Ca-ATPase have been isolated. The restriction map of the overlapping clones covers a region of 65 kilobases of DNA. Nucleotide sequence of mRNA coding regions shows that the gene is divided into 18 exons separated by 17 introns. Compared with the structure of the rabbit sarco(endo)plasmic reticulum Ca-ATPase 1 gene, 12 of the introns are in the same position, 8 introns present in the rabbit gene are absent from A. franciscana, 4 introns present in A. franciscana are not found in rabbit, and the position of 1 intron is shifted one base between both genes. Southern blot analysis strongly suggests that this is the only sarco(endo)plasmic reticulum Ca-ATPase gene present in A. franciscana. Primer extension and nuclease S1 protection experiments have shown the existence of two main regions of transcription initiation separated by 30 nucleotides. Transcription is initiated in both regions at two or three consecutive bases. A hexanucleotide that includes the initiation sites is repeated in both transcription initiation regions. The nucleotide sequence of the promoter region shows the existence of several putative regulatory sites, including some that are muscle-specific such as one CArG box, 3 MEF-2, and 8 putative binding sites for muscle transcription factors of the MyoD family.

Cloning and expression of a novel, highly truncated phosphoinositide-specific phospholipase C cDNA from embryos of the brine shrimp, Artemia

A novel, highly truncated form of a cDNA encoding Artemia phosphoinositide-specific phospholipase C (PLC), designated PLC-beta x, was isolated from a brine shrimp cDNA library. The full-length cDNA is of the beta-type, it is 2855 base pairs long, and it contains an open reading frame encoding 489 amino acids. The deduced amino acid sequence of PLC-beta c cDNA shows novel features. It lacks several hundred amino acids at the 5' end, as compared to PLC-beta s in the higher species. It contains conserved domains X and Y, but domain X is highly truncated at the 5' end (only 14-25 conserved amino acids as compared to about 150 amino acids in the higher eukaryotic organisms). Northern blot hybridization showed that the PLC-beta x cDNA corresponds to a 4.4-kilobase mRNA. Northern blot hybridization with a cDNA probe from the 5' end and PCR performed upstream from domain Y showed that PLC-beta x is not a cloning artifact due to fusion of an unrelated clone into the coding region of the PLC-beta homologue. A functional PLC and new protein bands on SDS-PAGE were observed after subcloning full-length PLC-beta x cDNA, as well as a fragment containing the conserved regions, into expression plasmid vectors and transfecting into Escherichia coli. 1 mM lithium markedly stimulated expression in E. coli.

Purification and properties of GTP:GTP guanylyltransferase from encysted embryos of the brine shrimp Artemia

GTP:GTP guanylyltransferase has been purified from the yolk platelets of Artemia cysts. The 480-kDa enzyme catalyzes the reversible reaction 2GTP<==>Gp4G + PPi and contains immunologically related polypeptides of 142, 88, and 45 kDa and a distinct 80-kDa component. The 88 and 45 kDa species can be covalently labeled with [alpha-32P]GTP. Even in crude extracts, the enzyme appears to be partially proteolyzed, suggesting that it is a nonfunctional residue of the pre-encystment stages of development. A native alpha 2 beta 2 structure comprising 2 mol each of the 142- and 80-kDa polypeptides is proposed. The reaction follows ping-pong kinetics with a covalent enzyme-guanylate intermediate containing a phosphoramidate linkage, probably phospholysine. The enzyme has two GTP-binding sites: a "donor" site in which the enzyme-guanylate is formed and which is highly specific for guanine nucleotides (GTP, p4G, dGTP, and GppNHp) and an "acceptor" site which additionally binds XTP, ITP, GDP, and ADP. Thus, the enzyme will form the homodinucleotides Gp4G, Gp5G, Gp3G, dGp4dG, and GppNHppG and the heterodinucleotides Gp4X, Gp4I, and Gp3A, but not Xp4X, Ip4I, or Gp4A. The Km for GTP was 6.7 mM and kcat was 1.6 s-1. XTP was a fully uncompetitive inhibitor of Gp4G synthesis while ITP was a partially uncompetitive inhibitor. In the reverse reaction, certain pyrophosphate analogs could substitute for PPi. The structure and mechanism of this enzyme suggest an evolutionary relationship to mRNA capping enzymes.

Glutamate 779, an intramembrane carboxyl, is essential for monovalent cation binding by the Na,K-ATPase

Incubation of purified renal Na,K-ATPase with the fluorescent carboxyl-selective reagent, 4-(diazomethyl)-7-(diethylamino)- coumarin (DEAC), results in enzyme inactivation via disruption of the monovalent cation binding sites and loss of K+ and Na+ binding capacity. Modification of 1 or 2 carboxyl residues in the alpha-subunit in a K+ or Na(+)-preventable manner leaves the ATP binding unaltered, and the enzyme is still able to undergo the major conformational transitions (Argüello, J. M., and Kaplan, J. H. (1991) J. Biol. Chem. 266, 14627-14635). Labeled alpha-subunits of Na,K-ATPase were isolated by gel electrophoresis and digested using V8 protease. The digests contained two bands which were fluorescently labeled in a cation-protectable fashion. Four peptides were identified in these bands. Peptides I (apparent molecular mass approximately 17 kDa), II (approximately 15 kDa), and IIIa (approximately 5 kDa) start at Gly758 while Peptide IIIb (approximately 5 kDa) starts at Gly561. Subsequent proteolysis of peptides IIIa and IIIb with thermolysin followed by electrophoresis revealed a single smaller fluorescent peptide which passed through 3-kDa cut-off membrane filters but was retained by 1-kDa cut off filters. N-terminal sequence analysis of this peptide gave the sequence 773Leu-Thr-Ser-Asn-Ile-Pro-Glu-Ile-Thr-Pro-Phe-Leu. The length of this peptide was also examined in labeling experiments with cysteine-reactive probes which indicated that the peptide did not extend to the next carboxyl-containing amino acid residue in the alpha-subunit sequence (Asp804). The site of attachment of DEAC is thus Glu779, an intramembrane carboxyl residue present in all known sequences of alpha-subunit isoforms of the Na,K-ATPase. This glutamate is essential for Na+ and K+ binding and active transport by the sodium pump. Its location in the fifth transmembrane segment provides a way in which information about ATP binding and phosphorylation in the major cytoplasmic loop of the enzyme is transmitted to intramembrane cation sites during the reaction cycle.

Variations in the activity of some metabolic enzymes during development of Artemia parthenogenetica (Crustacea: Anostraca)

Metabolic activity of the cysts as well as other developmental stages of Artemia parthenogenetica was determined by studying various key metabolic enzymes such as lactate dehydrogenase (LDH) and malate dehydrogenase (MDH). The electrophoretic studies on LDH show the existence of a single fraction uniformly in all the developmental stages of A. parthenogenetica. Electrophoretic patterns of MDH during the same stages show variations in isozymic fractions as development proceeds towards adults. Enzyme assay during lactate oxidation and pyruvate reduction of LDH as well as malate oxidation and oxaloacetate reduction of MDH in different developmental stages reveals that the anaerobic metabolism is more prevalent than the aerobic type. Further quantification of these enzymes shows that their activities are low and stable in the encysted gastrulae, and increase rapidly when the embryo emerges. One of the kinetic properties such as pH has impact on the general behavior of the enzymes throughout the developmental stages.

A tRNA(Ser)(UCN) gene in Artemia salina mitochondrial DNA: a case of mistaken identity

We have sequenced a segment of mitochondrial DNA (mtDNA) of a crustacean, the brine shrimp, Artemia salina, that includes 3' end-proximal regions of the genes for subunit 1 of the NADH dehydrogenase complex (ND1) and cytochrome b (Cyt b). From our data we conclude that in this mtDNA, as in the mtDNAs of Drosophila species, a tRNA(Ser)(UCN) gene separates the ND1 and Cyt b genes. This is contrary to an earlier report that the A. salina ND1 and Cyt b genes are immediately adjacent to each other.

Similar alternative splicing events generate two sarcoplasmic or endoplasmic reticulum Ca-ATPase isoforms in the crustacean Artemia franciscana and in vertebrates

A second isoform of the Artemia franciscana sarcoplasmic or endoplasmic reticulum Ca-ATPase has been identified through the isolation of cDNA clones. This isoform differs from the previously identified one only at the C-terminal end of the protein. The last 6 amino acids of the former isoform change to 30 hydrophobic amino acids in the newly identified isoform that have the potentiality of being an additional transmembrane domain. The two A. franciscana isoforms are highly homologous to the two isoforms coded by the mammalian and bird SERCA2 gene, except that the C-terminal extensions share their hydrophobic character but have no significant amino acid homology. The isolation of genomic clones coding for this region of the gene shows that both isoforms arise from the same gene by alternative splicing. The donor splicing site of the penultimate exon can either be recognized and fused to the last exon, giving rise to the mRNA coding for the shortest protein, or remain unrecognized, in which case a polyadenylation site is recognized before the last exon of the gene and the mRNA coding for the largest protein is originated. The alternative splicing used to originate the two isoforms is similar in Artemia and vertebrates. The conservation of the alternative splicing between species so distant in evolution suggests an important physiological role for the existence of the two isoforms of the protein.

Inhibition of casein kinase II by dinucleoside polyphosphates

In our search for potential inhibitors of casein kinase II (CKII) in Artemia, we have shown that dinucleoside polyphosphates are a novel class of effectors for this ubiquitous protein kinase. P1,P4-di(guanosine-5')-tetraphosphate (Gp4G) is a better CKII inhibitor than P1,P4-di(adenosine-5')-tetraphosphate (Ap4A). The inhibition by both effectors is more potent when GTP is used as phosphate donor instead of ATP. The inhibition of CKII increases with the number of phosphates linking the guanosine/adenosine moieties (for n = 2-6). Ap4A does not compete with the protein substrate and causes an increase in the apparent KmATP and a decrease in the apparent VmATP, indicating a mixed type of inhibition with respect to ATP.