Complete Genomic Structure of the Bloom-forming Toxic Cyanobacterium Microcystis aeruginosa NIES-843

The nucleotide sequence of the complete genome of a cyanobacterium, Microcystis aeruginosa NIES-843, was determined. The genome of M. aeruginosa is a single, circular chromosome of 5 842 795 base pairs (bp) in length, with an average GC content of 42.3%. The chromosome comprises 6312 putative protein-encoding genes, two sets of rRNA genes, 42 tRNA genes representing 41 tRNA species, and genes for tmRNA, the B subunit of RNase P, SRP RNA, and 6Sa RNA. Forty-five percent of the putative protein-encoding sequences showed sequence similarity to genes of known function, 32% were similar to hypothetical genes, and the remaining 23% had no apparent similarity to reported genes. A total of 688 kb of the genome, equivalent to 11.8% of the entire genome, were composed of both insertion sequences and miniature inverted-repeat transposable elements. This is indicative of a plasticity of the M. aeruginosa genome, through a mechanism that involves homologous recombination mediated by repetitive DNA elements. In addition to known gene clusters related to the synthesis of microcystin and cyanopeptolin, novel gene clusters that may be involved in the synthesis and modification of toxic small polypeptides were identified. Compared with other cyanobacteria, a relatively small number of genes for two component systems and a large number of genes for restriction-modification systems were notable characteristics of the M. aeruginosa genome

Brain Aromatase Modulates Serotonergic Neuron by Regulating Serotonin Levels in Zebrafish Embryos and Larvae

Teleost fish are known to express two isoforms of P450 aromatase, a key enzyme for estrogen synthesis. One of the isoforms, brain aromatase (AroB), cyp19a1b, is highly expressed during early development of zebrafish, thereby suggesting its role in brain development. On the other hand, early development of serotonergic neuron, one of the major monoamine neurons, is considered to play an important role in neurogenesis. Therefore, in this study, we investigated the role of AroB in development of serotonergic neuron by testing the effects of (1) estradiol (E2) exposure and (2) morpholino (MO)-mediated AroB knockdown. When embryos were exposed to E2, the effects were biphasic. The low dose of E2 (0.005 µM) significantly increased serotonin (5-HT) positive area at 48 hour post-fertilization (hpf) detected by immunohistochemistry and relative mRNA levels of tryptophan hydroxylase isoforms (tph1a, tph1b, and tph2) at 96 hpf measured by semi-quantitative PCR. To test the effects on serotonin transmission, heart rate and thigmotaxis, an indicator of anxiety, were analyzed. The low dose also significantly increased heart rate at 48 hpf and decreased thigmotaxis. The high dose of E2 (1 µM) exhibited opposite effects in all parameters. The effects of both low and high doses were reversed by addition of estrogen receptor (ER) blocker, ICI 182,780, thereby suggesting that the effects were mediated through ER. When AroB MO was injected to fertilized eggs, 5-HT-positive area was significantly decreased, while the significant decrease in relative tph mRNA levels was found only with tph2 but not with two other isoforms. AroB MO also decreased heart rate and increased thigmotaxis. All the effects were rescued by co-injection with AroB mRNA and by exposure to E2. Taken together, this study demonstrates the role of brain aromatase in development of serotonergic neuron in zebrafish embryos and larvae, implying that brain-formed estrogen is an important factor to sustain early development of serotonergic neuron

Intestinal uptake of lipovitellin from brine shrimp (Artemia franciscana) by larval inland silversides (Menidia beryllina) and striped bass (Morone saxatilis)

Intestinal uptake of lipovitellin (LV) from brine shrimp (Artemia franciscana) in larval inland silversides (Menidida beryllina) and striped bass (Morone saxatilis) was described using immunocytochemistry. Polyclonal antisera were raised against two subunits of LV (LV68 and LV190). When tested by immunocytochemistry, anti-LV68 showed cross-reactivity with some of the pancreatic cells especially in inland silversides. Therefore anti-LV190 was used to localize immunoreactive LV. Inland silversides at 14 days after hatching were fed Artemia nauplii and then sampled 4, 8, 12 hr after feeding. Similar experiments were carried out by using striped bass at 5 days and 15 days of age. They were sampled at 2, 4, 8, and 12 hr after feeding. Anterior enterocytes showed no evidence of uptake; however, the brush border of the cells of inland silversides reacted with the antiserum. Posterior enterocytes took up the LV and/or, possibly, their immunoreactive breakdown products. The pattern of uptake included accumulation in supranuclear vacuoles and digestion in supranuclear vacuoles, as suggested by the decay of the immunoreactivity over time. Thus, the posterior intestine of these larval fishes is the site of uptake and digestion of LV, an important nutritive component in the food of many larval fishes; this supports earlier findings using non-nutritive marker proteins

Estrogens disrupt serotonin receptor and cyclooxygenase mRNA expression in the gonads of mussels (Mytilus edulis)

Estrogenic contaminants in the aquatic environment are associated with feminisation of male fish, however their effects on some invertebrate species, such as bivalve molluscs, have yet to be characterised. Gametogenesis represents a critical step in the reproductive process and is subjected to hormonal control by serotonin (5-HT), prostaglandins (synthesised by cyclooxygenases-COX) and steroids such as 17 beta-estradiol (E2). Here, we examine the responses of 5-HT receptor and COX mRNA expression in mussels, Mytilus edulis, exposed to estrogenic compounds during different stages of their reproductive cycle. In mature mussels, 5-HT receptor mRNA expression decreased following E2 exposure. The opposite trend was observed in mussels at early gametogenesis stages. COX mRNA expression levels at both stages were generally decreased by E2 exposure. Mussels at early gametogenesis stages were also exposed to ethynylestradiol (EE2) and estradiol benzoate (EB) and a significant increase in 5-HT receptor mRNA expression was observed with both xeno-estrogens. COX expression levels were increased with EB exposure but no significant effects were found with EE2 exposure. These results show that the natural estrogen, E2, as well as the synthetic estrogen, EE2, induce alterations, dependent on reproductive stage, in the mRNA expression levels of 5-HT receptor and/or COX in the marine bivalve M. edulis. (C) 2010 Elsevier B.V. All rights reserved

Two CYP3A-like genes in the marine mussel Mytilus edulis: mRNA expression modulation following short-term exposure to endocrine disruptors

Members of the vertebrate CYP3A subfamily are involved in the metabolism of steroids and a wide range of xenobiotics. In this study two CYP3A- like mRNAs have been isolated from the mussel (Mytilus edulis), and their seasonal expression profile and modulation by estrogens examined. Sexual dimorphism of CYP3A- like mRNA expression was not observed in mussel gonads of individuals collected throughout a year. Nevertheless, natural variation in gonadal CYP3A- like mRNA expression was observed, with highest levels of CYP3A isoform1 and lowest levels of CYP3A isoform2 mRNA during the maturation and spawning season. Exposure to a 10% sewage treatment works extract did not result in any significant changes in mRNA expression of CYP3A-like. In contrast, exposure to E2 (200ng/L) and TBT (100ng/L) significantly down-regulated the expression of CYP3A- like isoform1 but not CYP3A-like isoform2 suggesting differential regulation. Understanding xenobiotic metabolism pathways in aquatic invertebrates

Estrogens disrupt serotonin receptor and cyclooxygenase mRNA expression in the gonads of mussels (Mytilus edulis)

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