Marine incursions,cryptic species and ecological diversification in Amazonia: the biogeographic history of the croaker genus Plagioscion (Sciaenidae)

Aim We propose a phylogenetic hypothesis for the marine‐derived sciaenid genus Plagioscion in the context of geomorphology and adaptation to freshwaters of South America, and assess the extent to which contemporary freshwater hydrochemical gradients influence diversification within a widely distributed Plagioscion species, Plagioscion squamosissimus. Location Amazon Basin and South America. Methods Using nuclear and mitochondrial DNA sequence data, phylogenetic analyses were conducted on the five nominal Plagioscion species, together with representatives from Pachyurus and Pachypops, using character and model‐based methods. Genealogical relationships and population genetic structure of 152 P. squamosissimus specimens sampled from the five major rivers and three hydrochemical settings/‘colours’ (i.e. white, black and clear water) of the Amazon Basin were assessed. Results Phylogenetic analyses support the monophyly of Plagioscion in South America and identify two putative cryptic species of Plagioscion. Divergence estimates suggest that the Plagioscion ancestor invaded South America via a northern route during the late Oligocene to early Miocene. Within P. squamosissimus a strong association of haplotype and water colour was observed, together with significant population structure detected between water colours. Main conclusions Our analyses of Plagioscion are consistent with a biogeographic scenario of early Miocene marine incursions into South America. Based on our phylogenetic results, the fossil record, geomorphological history and distributional data of extant Plagioscion species, we propose that marine incursions into western Venezuela between the late Oligocene and early Miocene were responsible for the adaptation to freshwaters in Plagioscion species. Following the termination of the marine incursions during the late Miocene and the establishment of the modern Amazon River, Plagioscion experienced a rapid diversification. Plagioscion squamosissimus arose during that time. The formation of the Amazon River probably facilitated population and range expansions for this species. Further, the large‐scale hydrochemical gradients within the Amazon Basin appear to be acting as ecological barriers maintaining population discontinuities in P. squamosissimus even in the face of gene flow. Our results highlight the importance of divergent natural selection through time in the generation and maintenance of sciaenid diversity in Amazonia.     

Modeling the Role of Negative Cooperativity in Metabolic Regulation and Homeostasis

A significant proportion of enzymes display cooperativity in binding ligand molecules, and such effects have an important impact on metabolic regulation. This is easiest to understand in the case of positive cooperativity. Sharp responses to changes in metabolite concentrations can allow organisms to better respond to environmental changes and maintain metabolic homeostasis. However, despite the fact that negative cooperativity is almost as common as positive, it has been harder to imagine what advantages it provides. Here we use computational models to explore the utility of negative cooperativity in one particular context: that of an inhibitor binding to an enzyme. We identify several factors which may contribute, and show that acting together they can make negative cooperativity advantageous.     

A novel regulatory role of TRAPPC9 in L-plastin-mediated osteoclast actin ring formation

Trafficking protein particle complex 9 (TRAPPC9) is a major subunit of the TRAPPII complex. TRAPPC9 has been reported to bind nuclear factor κB kinase subunit β (IKKβ) and NF-kB-inducing kinase (NIK) where it plays a role in the canonical and noncanonical of nuclear factor-κB (NF-kB) signaling pathways, receptively. The role of TRAPPC9 in protein trafficking and cytoskeleton organization in osteoclast (OC) has not been studied yet. In this study, we examined the mRNA expression of TRAPPC9 during OC differentiation. Next, we examined the colocalization of TRAPPC9 with cathepsin-K, known to mediate OC resorption suggesting that TRAPPC9 mediates the trafficking pathway within OC. To identify TRAPPC9 protein partners important for OC-mediated cytoskeleton re-organization, we conducted immunoprecipitation of TRAPPC9 in mature OCs followed by mass spectrometry analysis. Our data showed that TRAPPC9 binds various protein partners. One protein with high recovery rate is L-plastin (LPL). LPL localizes at the podosomes and reported to play a crucial role in actin aggregation thereby actin ring formation and OC function. Although the role of LPL in OC-mediated bone resorption has not fully reported in detail. Here, first, we confirmed the binding of LPL to TRAPPC9 and, then, we investigated the potential regulatory role of TRAPPC9 in LPL-mediated OC cytoskeleton reorganization. We assessed the localization of TRAPPC9 and LPL in OC and found that TRAPPC9 is colocalized with LPL at the periphery of OC. Next, we determined the effect of TRAPPC9 overexpression on LPL recruitment to the actin ring using a viral system. Interestingly, our data showed that TRAPPC9 overexpression promotes the recruitment of LPL to the actin ring when compared with control cultures. In addition, we observed that TRAPPC9 overexpression reorganizes actin clusters/aggregates and regulates vinculin recruitment into the OC periphery to initiate podosome formation.     

Growth Phase-Dependent Regulation of Vsr Endonuclease May Contribute to 5-Methylcytosine Mutational Hot Spots in Escherichia coli

Using rabbit polyclonal antibodies, we have shown that the Dcm cytosine methylase of Escherichia coli is maintained at a constant level during cell growth, while Vsr endonuclease levels are growth phase dependent. Decreased production of Vsr relative to Dcm during the log phase may contribute substantially to the mutability of 5-methylcytosine.     

Characterization of the Fc gamma receptor on human platelets

IgG-containing immune complexes may play a role in the immune destruction of human platelets by interacting with an Fc gamma receptor on the platelet surface. We studied the platelet Fc gamma receptor and characterized its interaction with IgG ligand and anti-Fc gamma receptor monoclonal antibodies. Oligomers of IgG, but not monomeric IgG, bound to platelets and the number of binding sites was significantly increased at low ionic strength. Ligand-binding studies indicated that normal human platelets express a single Fc gamma receptor (Fc gamma RII) with 8559 +/- 852 sites per cell, Kd = 12.5 +/- 1.7 X 10(-8) M using trimeric IgG. Results of studies with bivalent and Fab monoclonal anti-Fc gamma RII were consistent with each Fc gamma receptor expressing two epitopes recognized by the antibody. The number of Fc gamma binding sites and affinity of binding were unchanged by the presence of 2.0 mM Mg2+ or 10 micrograms/ml cytochalasin B. Platelet stimulation with thrombin or ADP in the presence of fibrinogen also did not alter the number of Fc gamma binding sites or the affinity of binding. However, platelets preincubated with 5 microM dexamethasone expressed a decreased number of Fc gamma binding sites as well as decreased IgG-dependent platelet aggregation. Platelets from patients with Glanzmann's thrombasthenia and from patients with the Bernard Soulier syndrome expressed a normal number and affinity of Fc gamma binding sites. The data suggest that platelet Fc gamma RII binding of trimeric IgG occurs independent of actin filament interaction, Mg2+, ADP, or thrombin and does not require GPIIb/IIIa or GPIIb/IIIa-fibrinogen interaction. Furthermore, this receptor appears to be normally expressed on GPIb-deficient platelets and susceptible to modulation by glucocorticoids. Finally, the Fc gamma-binding protein was isolated from whole platelets as a 220-kDa protein which upon reduction dissociates into 50,000 Mr subunits.     

3-Mercaptopropionic acid administration increases the affinity of [H]Quinuclidinyl benzilate binding to membranes of the striatum and cerebellum

It is known that quinuclidinyl benzilate (QNB) binds specifically and with high affinity to the cholinergic muscarinic receptor and that behaves as a potent antagonist of this receptor.

We have analysed -[³H]QNB binding to rat CNS membranes after the administration of the convulsant 3-mercaptopropionic acid (MP) (150 mg·kg⁻¹, i.p.). The studies were done in rats killed at two stages: during and after seizures. No changes in [³H]QNB binding to hippocampus and cerebral cortex membranes were found. [³H]QNB binding increased about 40 and 80% in striatum and cerebellum membranes, respectively. The changes were observed both in seizure and postseizures states. The study was extended to the assay of [³H]QNB binding kinetic constants in the anatomical areas modified by the convulsant. The analysis of the saturation curves indicated an increase in the binding affinity but no change in the number of binding sites. Hill number values were near the unit suggesting a non-cooperative interaction between the ligand and the receptor, and the labelling of a homogeneous population of receptor sites.

The results suggest the participation of some cholinergic pathways in the development and maintenance of MP-induced seizures.     

Expectations of assisted conception for infertility.

OBJECTIVE--To provide reliable prognostic information for couples seeking assisted conception. DESIGN--Analysis of four years'' practice (1988-91). SETTING--Private university service linked with NHS reproductive medicine services. PATIENTS--804 couples with various causes of subfertility, median duration five years, median age of women 34 years. INTERVENTIONS--1280 completed cycles: 950 in vitro fertilisation, 144 gamete intrafallopian transfer, and 186 intrauterine insemination and superovulation. MAIN OUTCOME MEASURES--Pregnancy and birth rates per cycle and cumulative pregnancy and take home baby rates per couple. RESULTS--In women under 40 years and men with normal sperm, whatever the cause of infertility, results with in vitro fertilisation improved steadily reaching a pregnancy rate per cycle of 30% (95% confidence interval 26% to 35%) during 1990-1 and birth rate per cycle of 29% (23% to 35%) in 1990. Pregnancy and birth rates for gamete intrafallopian transfer were 36% (28% to 44%) and 26% (17% to 37%) and for intrauterine insemination 18% (12% to 24%) and 16% (10% to 22%). After six cycles cumulative probability of pregnancy was 82% and cumulative take home baby rate 70%. Considering only in vitro fertilisation and gamete intrafallopian transfer after four cycles the pregnancy rate was 78% (66% to 91%). CONCLUSIONS--Conception is less likely in women over 40 and men with sperm dysfunction. For other couples the prognosis for a live birth is at least as good as for fertile couples if they persist with treatment.     

Stimulation of ribosomal RNA synthesis during hypertrophic growth of cultured heart cells by phorbol ester

Primary cultures of neonatal cardiac myocytes were used to determine the effects of tumor-promoting phorbol esters on ribosomal RNA (rRNA) synthesis during myocyte growth. Treatment of myocytes with phorbol-12,13-dibutyrate (PDBu) increased protein accumulation by 25% and RNA content by 20%. Rates of rRNA synthesis were measured to assess the mechanism by which rRNA accumulated during myocyte growth. Rates of rRNA synthesis were determined from the incorporation of [³H]uridine into UMP of purified rRNA and the specific radioactivity of the cellular UTP pool. After 24h of PDBu treatment, cellular rates of 18S and 28S rRNA synthesis were accelerated by 67% and 64%, respectively. The increased rate of rRNA synthesis accounted for the net increase in myocyte rRNA content after PDBu treatment.