An integrative approach to unravel the Ceratitis FAR (Diptera,Tephritidae) cryptic species complex: a review

This paper reviews all information gathered from different disciplines and studies to resolve the species status within the Ceratitis FAR (Ceratitis fasciventris, Ceratitis anonae, Ceratitis rosa) complex, a group of polyphagous fruit fly pest species (Diptera, Tephritidae) from Africa. It includes information on larval and adult morphology, wing morphometrics, cuticular hydrocarbons, pheromones, microsatellites, developmental physiology and geographic distribution. The general consensus is that the FAR complex comprises Ceratitis anonae, two species within Ceratitis rosa (so-called R1 and R2) and two putatitve species under Ceratitis fasciventris. The information regarding the latter is, however, too limited to draw final conclusions on specific status. Evidence for this recognition is discussed with reference to publications providing further details.     

Elevated carbon dioxide blunts mammalian cAMP signaling dependent on inositol 1,4,5-triphosphate receptor-mediated Ca2+ release

Elevated CO(2) is generally detrimental to animal cells, suggesting an interaction with core processes in cell biology. We demonstrate that elevated CO(2) blunts G protein-activated cAMP signaling. The effect of CO(2) is independent of changes in intracellular and extracellular pH, independent of the mechanism used to activate the cAMP signaling pathway, and is independent of cell context. A combination of pharmacological and genetic tools demonstrated that the effect of elevated CO(2) on cAMP levels required the activity of the IP(3) receptor. Consistent with these findings, CO(2) caused an increase in steady state cytoplasmic Ca(2+) concentrations not observed in the absence of the IP(3) receptor or under nonspecific acidotic conditions. We examined the well characterized cAMP-dependent inhibition of the isoform 3 Na(+)/H(+) antiporter (NHE3) to demonstrate a functional relevance for CO(2)-mediated reductions in cellular cAMP. Consistent with the cellular biochemistry, elevated CO(2) abrogated the inhibitory effect of cAMP on NHE3 function via an IP(3) receptor-dependent mechanism.     

Polyunsaturated fatty acids inhibit PI3K activity in a yeast-based model system

The phosphatidylinositol 3-kinase (PI3K) pathway controls the regulation of cell growth, proliferation, migration and apoptosis. In many tumors, the PI3K gene is mutated or overexpressed, and/or the PI3K pathway is hyperactive. PI3K is therefore a potential pharmacological target for the development of anti-tumor drugs. Some polyunsaturated fatty acids (PUFA), when given in the diet, may lead to a decrease in PI3K activity. We used a yeast-based model to reconstitute the PI3K/PTEN/Akt pathway to study the effects of long-chain polyunsaturated n-3 fatty acids on PI3K, and found that various PUFA were able to alleviate toxicity induced by overexpression of PI3K. The various PUFA had no significant effect on the steady-state level of PI3K catalytic subunit proteins (p110α) in yeast. However, depletion of phosphatidylinositol 4,5-bisphosphate due to overexpression of the p110α subunit was significantly reduced by treating the yeast cells with the various PUFA. The inhibition of mammalian PI3K, expressed in an exogenous cellular context in yeast, is likely to be a direct effect of these PUFA on PI3K rather than on other mammalian endogenous or environmental factors. These results are particularly promising given the abundance of active PUFA in marine foodstuffs and especially fish oils.     

Response of archaeal communities in the rhizosphere of maize and soybean to elevated atmospheric CO2 concentrations

Background

Archaea are important to the carbon and nitrogen cycles, but it remains uncertain how rising atmospheric carbon dioxide concentrations ([CO₂]) will influence the structure and function of soil archaeal communities.

Methodology/Principal Findings

We measured abundances of archaeal and bacterial 16S rRNA and amoA genes, phylogenies of archaeal 16S rRNA and amoA genes, concentrations of KCl-extractable soil ammonium and nitrite, and potential ammonia oxidation rates in rhizosphere soil samples from maize and soybean exposed to ambient (∼385 ppm) and elevated (550 ppm) [CO₂] in a replicated and field-based study. There was no influence of elevated [CO₂] on copy numbers of archaeal or bacterial 16S rRNA or amoA genes, archaeal community composition, KCl-extractable soil ammonium or nitrite, or potential ammonia oxidation rates for samples from maize, a model C₄ plant. Phylogenetic evidence indicated decreased relative abundance of crenarchaeal sequences in the rhizosphere of soybean, a model leguminous-C₃ plant, at elevated [CO₂], whereas quantitative PCR data indicated no changes in the absolute abundance of archaea. There were no changes in potential ammonia oxidation rates at elevated [CO₂] for soybean. Ammonia oxidation rates were lower in the rhizosphere of maize than soybean, likely because of lower soil pH and/or abundance of archaea. KCl-extractable ammonium and nitrite concentrations were lower at elevated than ambient [CO₂] for soybean.

Conclusion

Plant-driven shifts in soil biogeochemical processes in response to elevated [CO₂] affected archaeal community composition, but not copy numbers of archaeal genes, in the rhizosphere of soybean. The lack of a treatment effect for maize is consistent with the fact that the photosynthesis and productivity of maize are not stimulated by elevated [CO₂] in the absence of drought.     

Evolution of DNA Replication Protein Complexes in Eukaryotes and Archaea

Background

The replication of DNA in Archaea and eukaryotes requires several ancillary complexes, including proliferating cell nuclear antigen (PCNA), replication factor C (RFC), and the minichromosome maintenance (MCM) complex. Bacterial DNA replication utilizes comparable proteins, but these are distantly related phylogenetically to their archaeal and eukaryotic counterparts at best.

Methodology/Principal Findings

While the structures of each of the complexes do not differ significantly between the archaeal and eukaryotic versions thereof, the evolutionary dynamic in the two cases does. The number of subunits in each complex is constant across all taxa. However, they vary subtly with regard to composition. In some taxa the subunits are all identical in sequence, while in others some are homologous rather than identical. In the case of eukaryotes, there is no phylogenetic variation in the makeup of each complex—all appear to derive from a common eukaryotic ancestor. This is not the case in Archaea, where the relationship between the subunits within each complex varies taxon-to-taxon. We have performed a detailed phylogenetic analysis of these relationships in order to better understand the gene duplications and divergences that gave rise to the homologous subunits in Archaea.

Conclusion/Significance

This domain level difference in evolution suggests that different forces have driven the evolution of DNA replication proteins in each of these two domains. In addition, the phylogenies of all three gene families support the distinctiveness of the proposed archaeal phylum Thaumarchaeota.     

Functional analysis of multiple single-stranded DNA-binding proteins from Methanosarcina acetivorans and their effects on DNA synthesis by DNA polymerase BI

Single-stranded DNA-binding proteins and their functional homologs, replication protein A, are essential components of cellular DNA replication, repair and recombination. We describe here the isolation and characterization of multiple replication protein A homologs, RPA1, RPA2, and RPA3, from the archaeon Methanosarcina acetivorans. RPA1 comprises four single-stranded DNA-binding domains, while RPA2 and RPA3 are each composed of two such domains and a zinc finger domain. Gel filtration analysis suggested that RPA1 exists as homotetramers and homodimers in solution, while RPA2 and RPA3 form only homodimers. Unlike the multiple RPA proteins found in other Archaea and eukaryotes, each of the M. acetivorans RPAs can act as a distinct single-stranded DNA-binding protein. Fluorescence resonance energy transfer and fluorescence polarization anisotropy studies revealed that the M. acetivorans RPAs bind to as few as 10 single-stranded DNA bases. However, more stable binding is achieved with single-stranded DNA of 18-23 bases, and for such substrates the estimated Kd was 3.82 +/- 0.28 nM, 173.6 +/- 105.17 nM, and 5.92 +/- 0.23 nM, for RPA1, RPA2, and RPA3, respectively. The architectures of the M. acetivorans RPAs are different from those of hitherto reported homologs. Thus, these proteins may represent novel forms of replication protein A. Most importantly, our results show that the three RPAs and their combinations highly stimulate the primer extension capacity of M. acetivorans DNA polymerase BI. Although bacterial SSB and eukaryotic RPA have been shown to stimulate DNA synthesis by their cognate DNA polymerases, our findings provide the first in vitro biochemical evidence for the conservation of this property in an archaeon.     

Ventral axial organs regulate expression of myotomal Fgf-8 that influences rib development

Fgf-8 encodes a secreted signaling molecule mediating key roles in embryonic patterning. This study analyzes the expression pattern, regulation, and function of this growth factor in the paraxial mesoderm of the avian embryo. In the mature somite, expression of Fgf-8 is restricted to a subpopulation of myotome cells, comprising most, but not all, epaxial and hypaxial muscle precursors. Following ablation of the notochord and floor plate, Fgf-8 expression is not activated in the somites, in either the epaxial or the hypaxial domain, while ablation of the dorsal neural tube does not affect Fgf-8 expression in paraxial mesoderm. Contrary to the view that hypaxial muscle precursors are independent of regulatory influences from axial structures, these findings provide the first evidence for a regulatory influence of ventral, but not dorsal axial structures on the hypaxial muscle domain. Sonic hedgehog can substitute for the ventral neural tube and notochord in the initiation of Fgf-8 expression in the myotome. It is also shown that Fgf-8 protein leads to an increase in sclerotomal cell proliferation and enhances rib cartilage development in mature somites, whereas inhibition of Fgf signaling by SU 5402 causes deletions in developing ribs. These observations demonstrate: (1) a regulatory influence of the ventral axial organs on the hypaxial muscle compartment; (2) regulation of epaxial and hypaxial expression of Fgf-8 by Sonic hedgehog; and (3) independent regulation of Fgf-8 and MyoD in the hypaxial myotome by ventral axial organs. It is postulated that the notochord and ventral neural tube influence hypaxial expression of Fgf-8 in the myotome and that, in turn, Fgf-8 has a functional role in rib formation.