Variability in the carbon isotope signature of Prochilodus lineatus (Prochilodontidae, Characiformes) a bottom-feeding fish of the Neotropical region

The spatial and seasonal variability of stable carbon isotopes in detritivorous Prochilodus lineatus , primary producers and particulate organic carbon (POC) were examined to promote a better understanding of the trophic dynamics of food webs in Neotropical ecosystems. Spatial variability in carbon isotope composition in the species showed a decreasing gradient in the Upper Paraná River system, from the Paraná River and Itaipu Reservoir subsystems to the Baía and Ivinheima subsystems. Fish δ¹³C followed the isotopic trend of POC along the Paraná River and Baía subsystem. Seasonal differences were not observed in fish. The analysis of percentile contribution of C₃ and C₄ sources in the species diet revealed the predominance of C₃ plants (phytoplanktonic and periphytic algae and riparian vegetation) in most of the analysed subsystems and seasons. Nevertheless, the considerable participation of riparian vegetation was verified, especially in the Ivinheima subsystem in the dry season. C₄ macrophytes presented a maximum contribution along the Upper Paraná River. These results demonstrate the existence of specific variability for the consumer and their food sources in different environments of the same ecosystem.     

Repetitive DNA and meiotic behavior of sex chromosomes in Gymnotus pantanal (Gymnotiformes, Gymnotidae)

Neotropical fishes have a low rate of chromosome differentiation between sexes. The present study characterizes the first meiotic analysis of sex chromosomes in the order Gymnotiformes. Gymnotus pantanal - females had 40 chromosomes (14m/sm, 26st/a) and males had 39 chromosomes (15m/sm, 24st/a), with a fundamental number of 54 - showed a multiple sexual determination chromosome system of the type X(1)X(1)X(2)X(2)/X(1)X(2)Y. The heterochromatin is restricted to centromeres of all chromosomes of the karyotype. The meiotic behavior of sex chromosomes involved in this system in males is from a trivalent totally pared in the pachytene stage, with a high degree of similarity. The cells of metaphase II exhibit 19 and 20 chromosomes, normal disjunction of sex chromosomes and the formation of balanced gametes with 18 + Y and 18 + X(1)X(2) chromosomes, respectively. The small amount of heterochromatin and repetitive DNA involved in this system and the high degree of chromosome similarity indicated a recent origin of the X(1)X(1)X(2)X(2)/X(1)X(2)Y system in G. pantanal and suggests the existence of a simple ancestral system with morphologically undifferentiated chromosomes.     

Cytogenetic analysis of Australian tiger beetles (Coleoptera: Cicindelidae): chromosome number, sex-determining system and localization of rDNA genes

The chromosomes of four species of Australian tiger beetle are documented. The male meioformulae of three species of Cicindela (tribe Cicindelini) were determined as follow: Cicindela cardinalba Sumlin 1987, n = 10 + X₁ X₂ X₃Y; C. sp. ( saetigera group) and Cicindela gillesensis Hudson 1994, n = 11 + X₁ X₂ X₃Y. The male meioformula of Megacephala whelani Sumlin 1992 (tribe Megacephalini) is n = 12 + XY. Fluorescence in situ hybridization (FISH) was used to localize the 18S-28S ribosomal gene clusters on male mitotic and meiotic chromosomes and nuclei using a polymerase chain reaction-amplified ribosomal probe. Fluorescence in mitosis and meiotic first prophase stages in the three Cicindela species showed that rDNA genes are in two of the four chromosomes that form the sex vesicle. In M. whelani hybridization in mitosis and first metaphase stages indicate that rDNA genes are in three, medium- to small-sized, autosomal pairs. Silver staining of male meiotic nuclei reveals the presence of active nucleolar organizing regions (NORs) in the sex vesicle of the three species of Cicindela . The cytogenetic and evolutionary implications of these findings are discussed.     

Classical and molecular cytogenetics of Atherinella brasiliensis (Teleostei, Atheriniformes) from South coast of Brazil

Cytogenetic studies were performed on specimens of Atherinella brasiliensis from Laranjeiras Bay (Paraná State, Brazil). All specimens had a diploid number of 48 chromosomes, with a karyotype constituted by 4m+14sm+18st+12a and fundamental number of 84. The C-positive heterochromatin was distributed over the nucleolar organizer regions (NORs) in the centromeric regions and on short arms of metacentric and submetacentric chromosomes. Most of this heterochromatin was AT-rich, except in the NORs, which were rich in GC, as detected by double staining with chromomycin A₃/4'-6-diamin-2-phenylindole. Single NORs were located at terminal positions of a submetacentric pair, as confirmed by fluorescent in situ hybridization with 18S rDNA probes. Both techniques showed a size heteromorphism between the homologous chromosomes. The 5S rDNA clusters were located in terminal positions on two chromosomal pairs and also displayed a size heteromorphism. Despite the conserved diploid number, the data on the karyotype microstructure help characterize the cytogenetic profile of this group.     

Molecular characterization and physical mapping of two classes of 5S rDNA in the genomes of Gymnotus sylvius and G. inaequilabiatus (Gymnotiformes, Gymnotidae)

The nucleotide sequences of the 5S rRNA multigene family and their distribution across the karyotypes in 2 species of Gymnotiformes, genus Gymnotus (G. sylvius and G. inaequilabiatus) were investigated by means of fluorescence in situ hybridization (FISH). The results showed the existence of 2 distinct classes of 5S rDNA sequences in both species: class I and class II. A high conservative pattern of the codifying region of the 5S rRNA gene was identified, contrasting with significant alterations detected in the nontranscribed spacer (NTS). The presence of TATA-like sequences along the NTS of both species was an expected occurrence, since such sequences have been associated with the regulation of the gene expression. FISH using 5S rDNA class I and class II probes revealed that both gene classes were collocated in the same chromosome pair in the genome of G. sylvius, while in that of G. inaequilabiatus, class II appeared more disperse than class I.     

Gymnotus capanema, a new species of electric knife fish (Gymnotiformes, Gymnotidae) from eastern Amazonia, with comments on an unusual karyotype

Gymnotus capanema n. sp. is described on the basis of cytogenetic, morphometric, meristic and osteological data from nine specimens (one male and eight females) from the municipality of Capanema, Pará, in the eastern Amazon of Brazil. Later, three additional specimens were found in museums and regarded as nontypes (not cytogenetically analysed). Gymnotus capanema, which occurs in sympatry with Gymnotus cf. carapo cytotype 2n = 42 (30m/sm + 12st/a) exhibits a novel karyotype for the genus, with 2n = 34 (20m/sm + 14st/a). Gymnotus capanema can be unambiguously diagnosed from all congeners on the basis of a combination of characters from external anatomy, pigmentation and osteology. The constitutive heterochromatin, rich in adenine-thymine (A-T) base pairs [4',6 diamidino-2-phenylindole dihydrochloride (DAPI) positive], occurs in the centromeric region of all of the chromosomes, and in the pericentromeric and the entire short arm of some chromosomes. The nucleolar organizing region (NOR), stained by silver nitrate, chromomycin A(3) (CMA(3)) and 18S ribosomal (r)DNA fluorescence in situ hybridization (FISH), occurs in the short arm of pair 15. FISH, with telomeric probes did not show interstitial telomeric sequences (ITS), despite the reduced 2n in comparison to the karyotypes of other species of Gymnotus. The karyotype of G. capanema, with a reduced 2n, is strikingly different from all other previously studied congeners.     

Microglial phagocytosis attenuated by short-term exposure to exogenous ATP through P2X7 receptor action

Microglia, the CNS resident macrophages responsible for the clearance of degenerating cellular fragments, are essential to tissue remodeling and repair after CNS injury. ATP can be released in large amounts after CNS injury and may mediate microglial activity through the ionotropic P2X and the metabotropic P2Y receptors. This study indicates that exposure to a high concentration of ATP for 30 min rapidly induces changes of the microglial cytoskeleton, and significantly attenuates microglial phagocytosis. A pharmacological approach showed that ATP-induced inhibition of microglial phagocytotic activity was due to P2X₇R activation, rather than that of P2YR. Activation of P2X₇R by its agonist, 2'-3'- O -(4-benzoyl)benzoyl-ATP (BzATP), produced a Ca²⁺-independent reduction in microglial phagocytotic activity. In addition, the knockdown of P2X₇R expression by lentiviral-mediated shRNA interference or the blockade of P2X₇R activation by the specific antagonists, oxidized ATP (oxATP) and brilliant blue G, has efficiently restored the phagocytotic activity of ATP and BzATP-treated microglia. Our results reveal that P2X₇R activation may induce the formation of a Ca²⁺-independent signaling complex, which results in the reduction of microglial phagocytosis. This suggests that exposure to ATP for a short-term period may cause insufficient clearance of tissue debris by microglia through P2X₇R activation after CNS injury, and that blockade of this receptor may preserve the phagocytosis of microglia and facilitate CNS tissue repair.     

Sex chromosome variability outlines the pathway to the chromosomal evolution in Microtus thomasi (Rodentia, Arvicolinae)

The underground vole Microtus thomasi , a Balkan endemic, displays remarkable variability in sex chromosome size and morphology. In the present study, we demonstrate this variability in two of its chromosomal races with 2 n  = 44 (i.e. 'thomasi' and 'atticus') with the use of C-banding on a sample of 189 individuals from 50 localities of Greece. In 'thomasi', five different, acrocentric X chromosome variants (X₀–X₄) are described, which differ significantly in size, due to heterochromatin addition. Also, three Y chromosome variants are described (Y₀–Y₂), ranging in size from very small (Y₀) to large (Y₂). The 'atticus' race displays three subtelocentric variants of the X chromosome (X_st0–X_st2), which differ in arm length ratio and heterochromatin content. In Peloponnesus, males of this race exhibit Y₀ and Y₁, whereas, in Attiki (south-east Sterea Ellada), males carry the small metacentric, Y_m. Overall, there is a trend towards sex chromosome size increase in a south to north direction. We propose that the last glaciation must have restricted M. thomasi to a refugium in southern Peloponnesus. During post-glacial colonization, limited northward expansion of its distribution area must have been accompanied by consecutive heterochromatin addition, which is proven today by comparatively larger sex chromosomes in the northern populations of 'thomasi' and 'atticus' in Greece than in their southern populations.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 685–695.     

P2X7 pre-synaptic receptors in adult rat cerebrocortical nerve terminals: a role in ATP-induced glutamate release

Although growing evidence suggests that extracellular ATP might play roles in the control of astrocyte/neuron crosstalk in the CNS by acting on P2X₇ receptors, it is still unclear whether neuronal functions can be attributed to P2X₇ receptors. In the present paper, we investigate the location, pharmacological profile, and function of P2X₇ receptors on cerebrocortical nerve terminals freshly prepared from adult rats, by measuring glutamate release and calcium accumulation. The preparation chosen (purified synaptosomes) ensures negligible contamination of non-neuronal cells and allows exposure of 'nude' release-regulating pre-synaptic receptors. To confirm the results obtained, we also carried out specific experiments on human embryonic kidney 293 cells which had been stably transfected with rat P2X₇ receptors. Together, our findings suggest that (i) P2X₇ receptors are present in a subpopulation of adult rat cerebrocortical nerve terminals; (ii) P2X₇ receptors are localized on glutamatergic nerve terminals; (iii) P2X₇ receptors play a significant role in ATP-evoked glutamate efflux, which involves Ca²⁺-dependent vesicular release; and (iv) the P2X₇ receptor itself constitutes a significant Ca²⁺-independent mode of exit for glutamate.     

Cytogenetics and chromosome banding patterns in Caesalpinioideae and Papilionioideae species of Pará, Amazonas, Brazil

Despite the abundance of woody legumes in Brazilian Amazonian rain forests, there are few chromosome counts on the native species of this important region. The present work presents such data for 13 species of Caesalpinioideae (the genera Bauhinia , Caesalpinia , Cassia , Chamaecrista and Senna ) and Papilionioideae ( Bowdichia , Centrosema and Dioclea ) collected from 17 natural populations. Our report represents the first chromosome counts for the genera Bowdichia and Dioclea and for four of the studied species. Observations are made on chromosome morphology, size, condensing behaviour and interphase nucleus structure. Banding with fluorochromes carried out for the first time in Caesalpinioideae revealed discrete CMA⁺/DAPI^– terminal (GC-rich) bands on 2–4 chromosome pairs of most species analysed, with a few species presenting discrete CMA^–/DAPI⁺ (AT-rich) bands. Significant differences in chromosome size, morphology and condensing behaviour were observed among members of the controversial tribe Cassieae ( Cassia , Chamaecrista and Senna ), revealing the tribe to be a heterogeneous group from the karyological point of view.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 181–191.     

Demonstration of the presence of alditols and galacturonic acid in Vibrio parahaemolyticus O10 lipopolysaccharide

Abstract Identification of 4 unidentified neutral substances (X₁, X₂, X₃ and X₄) in lipopolysaccharides of Vibrio parahaemolyticus (Miyano et al. (1980) FEMS Microbiol. Lett. 8, 23–28, and 14, 145–148) was attempted. X₁ (1,4-anhydroribitol) was found to be formed from ribitol-5-phosphate during hydrolysis. X₂ was identified to be 2- O -methylribitol. X₃ and X₄ were found to be formed during hydrolysis of galacturonic acid and D-glycero-L-mannoheptose (or L-glycero-D-mannoheptose), respectively. The chemical structures of X₃ and X₄ remain to be determined.     

P2X receptors-mediated cytosolic phospholipase A2 activation in primary afferent sensory neurons contributes to neuropathic pain

Activation of P2X₃ and P2X_2/3 receptors (P2X₃R/P2X_2/3R), ionotropic ATP receptor subtypes, in primary sensory neurons is involved in neuropathic pain, a debilitating chronic pain that occurs after peripheral nerve injury. However, the underlying mechanisms remain unknown. We investigated the role of cytosolic phospholipase A₂ (cPLA₂) as a downstream molecule that mediates the P2X₃R/P2X_2/3R-dependent neuropathic pain. We found that applying ATP to cultured dorsal root ganglion (DRG) neurons increased the level of Ser505-phosphorylated cPLA₂ and caused translocation of Ser505-phosphorylated cPLA₂ to the plasma membrane. The ATP-induced cPLA₂ activation was inhibited by a selective antagonist of P2X₃R/P2X_2/3R and by a selective inhibitor of cPLA₂. In the DRG in vivo , the number of cPLA₂-activated neurons was strikingly increased after peripheral nerve injury but not after peripheral inflammation produced by complete Freund's adjuvant. Pharmacological blockade of P2X₃R/P2X_2/3R reversed the nerve injury-induced cPLA₂ activation in DRG neurons. Moreover, administering the cPLA₂ inhibitor near the DRG suppressed nerve injury-induced tactile allodynia, a hallmark of neuropathic pain. Our results suggest that P2X₃R/P2X_2/3R-dependent cPLA₂ activity in primary sensory neurons is a key event in neuropathic pain and that cPLA₂ might be a potential target for treating neuropathic pain.     

Cytogenetic characterization of six species of flatfishes with comments to karyotype differentiation patterns in Pleuronectiformes (Teleostei)

The karyotypes and cytogenetic characteristics of flatfishes species Paralichthys orbignyanus , Paralichthys patagonicus , Citarichthys spilopterus and Etropus crossotus (Paralichthyidae), Bothus ocellatus (Bothidae) and Symphurus tessellatus (Cynoglossidae) were investigated by conventional [Giemsa staining, C-banding, Ag- and chromomycin (CMA₃)-stainings] and molecular [ in situ hybridization (ISH)] cytogenetic techniques. The results showed 2n = 46 and FN = 48 (2msm + 46sta) in P. orbignyanus , 2n = 46 and FN = 46 (46sta) in P. patagonicus , 2n = 26 and FN = 44 (18msm + 8sta) in C. spilopterus , 2n = 38 and FN = 64 (26msm + 12sta) in E. crossotus , 2n = 32 and FN = 50 (18msm + 14sta) in B. ocellatus , and 2n = 46 and FN = 62 (46msm + 62sta) in S. tessellatus . All species exhibited weak C-band positive segments in terminal and centromeric positions of some chromosome pairs. Silver staining of the nucleolus organizer regions (Ag-NOR) technique showed a single Ag-NOR-bearing chromosome pair in all species except E. crossotus . All these sites were CMA₃ positive and showed clear ISH signals after probing with a 18S rRNA probe. Etropus crossotus presented until seven chromosomes with Ag-NORs and CMA₃ positively stained segments in five chromosome pairs. Conversely only one chromosome pair was identified with the ISH experiments in this species. The available results show that the fishes of the order Pleuronectiformes experienced a marked chromosome evolution that included reduction in diploid number, mainly due to Robertsonian rearrangements, and several chromosome inversions.     

Physical mapping of 5S rDNA in two species of Knifefishes: Gymnotus pantanal and Gymnotus paraguensis (Gymnotiformes)

Physical mapping of 5S rDNA in 2 species of knifefishes, Gymnotuspantanal and G. paraguensis (Gymnotiformes), was performed using fluorescence in situ hybridization with a 5S rDNA probe. The 5S rDNA PCR product from the genomes of both species was also sequenced and aligned to determine non-transcribed spacer sequences (NTS). Both species under study had different patterns of 5S rDNA gene cluster distribution. While in the karyotype of G. pantanal two 5S rDNA-bearing pairs were observed, the karyotype of G. paraguensis possessed as many as 19 such pairs. Such multiplication of 5S rDNA gene clusters might be caused by the involvement of transposable elements because the NTS of G. paraguensis was 400 bp long with high identity (90%) with a mobile transposable element called Tc1-like transposon, described from the cyprinid fish Labeo rohita.     

Karyotypic diversity and evolution of seven mahseer species (Cyprinidae) from India

Mahseer is a group of fish species that are well known as food and game fishes. The taxonomy of the mahseer species is confusing owing to the morphological variations and habitat adaptation. Detailed karyomorphological investigations have been carried out in seven species of mahseer, using karyotyping, Ag-NOR and fluorescent staining techniques. The basic diploid chromosome number (2n), in all mahseer species, was observed to be 100; however, the karyotype formula varied among the species, which were recorded as: 20m + 14sm + 22st + 44t (fundamental arm number, FN = 134) in Tor khudree ; 22m + 24sm + 24st + 30t (FN = 146) in Tor mussullah; 12m + 22sm + 14st + 52t (FN = 134) in Tor putitora ; 20m + 24sm + 24st + 32t (FN = 144) in Tor tor ; 20m + 30sm + 24st + 26t (FN = 150) in Tor chelynoides; 20m + 20sm + 20st + 40t (FN = 140) in Tor progeneius; and 20m + 18sm + 14st + 48t (FN = 138) in Neolissochilus hexagonolepis . Silver staining of the chromosomes revealed the presence of multiple nucleolar organizer regions (NOR) in these mahseer species. The highest number of NORs was observed in T. tor (four pairs of chromosomes), whereas the other six species possessed Ag-NOR signals on only two pairs of chromosomes. Although chromomycin A₃ (CMA₃) staining induced bright fluorescence signals on same Ag-NORs sites, with CMA₃, one additional signal was observed on the p arm of subtelocentric chromosomes in T. tor , T. chelynoides , T. progeneius and N. hexagonolepis , which may indicate the presence of inactive NOR in these species. The information on cytogenetic profile of these mahseer species is discussed in the light of cytotaxonomic implications and understanding the karyoevolution of these fish species.     

Mechanism of abnormal growth in astrocytes derived from a mouse model of GM2 gangliosidosis

P2X receptors mediate a variety of physiological actions, including smooth muscle contraction, neuro-endocrine secretion and synaptic transmission. Among P2X receptors, the P2X₃ subtype is expressed in sensory neurons of dorsal root- and trigeminal-ganglia, where it performs a well-recognized role in sensory and pain transmission. Recent evidence indicates that the strength of P2X₃-mediated responses is modulated in vivo by altering the number of receptors at the plasma membrane. In the present study, we investigate the trafficking properties of P2X₃ receptor in transfected HEK293 cells and in primary cultures of dorsal root ganglion neurons, finding that P2X₃ receptor undergoes rapid constitutive and cholesterol-dependent endocytosis. We also show that endocytosis is accompanied by preferential targeting of the receptor to late endosomes/lysosomes, with subsequent degradation. Furthermore, we observe that at steady state the receptor localizes predominantly in lamp1-positive intracellular structures, with a minor fraction present at the plasma membrane. Finally, the level of functional receptor expressed on the cell surface is rapidly up-regulated in response to agonist stimulation, which also augments receptor endocytosis. The findings presented in this work underscore a very dynamic trafficking behavior of P2X₃ receptor and disclose a possible mechanism for the rapid modulation of ATP-mediated responses potentially relevant during physiological and pathological conditions.     

Variation in phytoplankton composition and limnological features in a water–water ecotone of the Lower Paraná Basin (Argentina)

1. Structure and dynamics of phytoplankton were studied at six sites in a reach of the Lower Paraná River floodplain, from the main course to a marginal shallow lake, connected through a stream. This system is defined as a water–water ecotone and thus, the aim of this work is to analyse the spatial changes of phytoplankton along the transitional system.
2. Temporal fluctuations in number of species and phytoplankton density were more pronounced in the river than in the shallow lake. Even though most species were ubiquitous, there was a clear segregation of the most abundant populations across the ecotone. Aulacoseira granulata var. granulata and other centric diatoms decreased towards the lentic system.
3. Transparency varied according to river discharge, being higher in the lake during high water phases, while the opposite behaviour was observed during dry periods. These fluctuations were related to precipitation and resuspension processes.
4. Nitrate concentration diminished towards the lake while soluble reactive phosphorus remained fairly homogeneous across the ecotone.     

ZZ/ZW sex chromosome system in an undescribed species of the genus Apareiodon (Characiformes, Parodontidae)

The chromosomes of an undescribed species of the genus Apareiodon (Characiformes, Parodontidae) from the Verde River, a headwater affluent of the Tibagi River (Paraná State, Brazil), were investigated using conventional Giemsa and Ag stainings, C-banding, CMA(3) fluorescence and fluorescent in situ hybridization (FISH) using 18S and 5S rDNA probes. The diploid chromosome number was 2n = 54, with the karyotype composed of 48 meta/submetacentric and six subtelocentric chromosomes in males, and 47 meta/submetacentric + seven subtelocentric chromosomes in females. The difference is hypothesized to be due to a ZZ/ZW heteromorphic sex chromosome system, a cytotaxonomic characteristic previously observed only in some species of the genus Parodon (family Parodontidae). The presence of similar and/or identical heteromorphic sex chromosome systems might suggest that species of the genera Parodon and Apareiodon bearing ZZ/ZW heteromorphic sex chromosomes likely constitute a monophyletic group, a hypothesis to be tested by a robust phylogeny of the family.     

Ionic regulation and Na+–K+-ATPase activity in gills and kidney of the freshwater stingray Paratrygon aiereba living in white and blackwaters in the Amazon Basin

During low-water period, freshwater stingray Paratrygon aiereba collected in the whitewater (WW) of the River Amazon showed higher urea content, osmolality, Na⁺ and Cl⁻ concentrations in plasma and perivisceral fluid than those caught in blackwater (BW) of the River Negro. Gills and kidney Na⁺–K⁺-ATPase activities were significantly lower in WW than in BW fish. The high level of kidney Na⁺–K⁺-ATPase activity in P. aiereba may minimize ion loss and generate diluted solute-free urine in ion-poor BW environment.     

A new species of Creagrutus Günther (Teleostei: Ostariophysi: Characiformes), from the upper Rio Paraná basin, central Brazil

Creagrutus varii n. sp. is described based on material from the Rio São Marcos basin, in the upper Rio Paraná system, Goiás State, Brazil. This is the first record of Creagrutus in the upper Rio Paraná. The new species is proposed to be the sister group of the remaining species of Creagrutus . Creagrutus varii differs from congeners in the morphology of the maxilla, primordial ligament, premaxillary dentition and other features. The evolution of premaxillary tooth morphology in Piabina and Creagrutus and the biogeography of the Rio Paranaíba basin are discussed.