The passionvine mealybug,Planococcus minor (Maskell) (Hemiptera: Pseudococcidae), and its natural enemies in the cocoa agroecosystem in Trinidad

Planococcus minor (Maskell) is native to South Asia, but it is also present in several Neotropical locations including the island of Trinidad in the southern Caribbean. The mealybug poses a serious threat to uninfested countries in this region as well as the mainland U.S. As part of an effort to gather much needed information on P. minor, 33 cocoa (Theobroma cacao L.) field sites on the island were surveyed in 2006 with a view to assess the occurrence and pest status of the mealybug. P. minor was identified from 20 field sites, indicating that it was well distributed across the island on this crop, which appeared to be a reliable indicator host plant. Infestation levels were generally low and populations were sparsely distributed across the field sites categorized into three habitat types. The following year, nine field sites were surveyed for natural enemies of P. minor using laboratory-infested potatoes in sentinel traps. Species from four insect orders and six families were collected and identified. The major predators belonged to the families Cecidomyiidae and Coccinellidae. Two primary parasitoids, Leptomastix dactylopii Howard (Encyrtidae) and Coccidoxenoides perminutus (Girault) (=Pauridia peregrina Timberlake, =Coccidoxenoides peregrinus (Timberlake)) (Encyrtidae), were reared from different mealybug stages, along with several hyperparasitoids. The primary parasitoids were probably introduced fortuitously. These diverse natural enemies were recovered throughout the sampling period from the different habitat types. The identification of key natural enemies associated with P. minor has important implications for the implementation of biological control in newly infested areas.     

Solid-state NMR studies of a diverged microsomal amino-proximate delta12 desaturase peptide reveal causes of stability in bilayer: tyrosine anchoring and arginine snorkeling

This study reports the solid-state NMR spectroscopic characterization of the amino-proximate transmembrane domain (TM-A) of a diverged microsomal delta12-desaturase (CREP-1) in a phospholipid bilayer. A series of TM-A peptides were synthesized with 2H-labeled side chains (Ala-53, -56, and -63, Leu-62, Val-50), and their dynamic properties were studied in 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) bilayers at various temperatures. At 6 mol % peptide to lipid, 31P NMR spectra indicated that the peptides did not significantly disrupt the phospholipid bilayer in the L(alpha) phase. The 2H NMR spectra from Ala-53 and Ala-56 samples revealed broad Pake patterns with quadrupolar splittings of 16.9 kHz and 13.3 kHz, respectively, indicating restricted motion confined within the hydrocarbon core of the phospholipid bilayer. Conversely, the deuterated Ala-63 sample revealed a peak centered at 0 kHz with a linewidth of 1.9 kHz, indicating increased side-chain motion and solvent exposure relative to the spectra of the other Ala residues. Val-50 and Leu-62 showed Pake patterns, with quadrupolar splittings of 3.5 kHz and 3.7 kHz, respectively, intermediate to Ala-53/Ala-56 and Ala-63. This indicates partial motional averaging and supports a model with the Val and Leu residues embedded inside the lipid bilayer. Solid-state NMR spectroscopy performed on the 2H-labeled Ala-56 TM-A peptide incorporated into magnetically aligned phospholipid bilayers indicated that the peptide is tilted 8 degrees with respect to the membrane normal of the lipid bilayer. Snorkeling and anchoring interactions of Arg-44 and Tyr-60, respectively, with the polar region or polar hydrophobic interface of the lipid bilayer are suggested as control elements for insertional depth and orientation of the helix in the lipid matrix. Thus, this study defines the location of key residues in TM-A with respect to the lipid bilayer, describes the conformation of TM-A in a biomembrane mimic, presents a peptide-bilayer model useful in the consideration of local protein folding in the microsomal desaturases, and presents a model of arginine and tyrosine control of transmembrane protein stability and insertion.     

Maternal cyclin B levels "Chk" the onset of DNA replication checkpoint control in Drosophila

In many animals, early development of the embryo is characterized by synchronous, biphasic cell divisions. These cell divisions are controlled by maternally inherited proteins and RNAs. A critical question in developmental biology is how the embryo transitions to a later pattern of asynchronous cell divisions and transfers the prior maternal control of development to the zygotic genome. The most-common model regarding how this transition from maternal to zygotic control is regulated posits that this is a consequence of the limitation of maternal gene products, due to their titration during early cell divisions. Here we discuss a recent article by Crest et al.1 that instead proposes that the balance of Cyclin-dependent Kinase 1 and Cyclin B (Cdk1-CycB) activity relative to that of the Drosophila checkpoint kinase Chk1 determines when asynchronous divisions begin.     

Slow and fast pulses in 1-D cultures of excitatory neurons

We analyze the characteristics of front propagation in activity of 1-D neuronal cultures by numerical simulations, using only excitatory dynamics. Experimental results in 1-D cultures of hippocampal neurons from rats have shown the spontaneous generation of a slow, low amplitude pulse that precedes a high amplitude, fast pulse that propagates through all the system. Notably, this transition appears both with and without the presence of functioning inhibitory synapses. In accordance with previous work, we demonstrate that purely excitatory integrate and fire neurons with depression in the synapses suffice to produce fast and uniform pulses but cannot explain the appearance of slow, weak pulses. We propose to explain the slow pulses by increasing the complexity of the neuron model in a purely excitatory network with connectivity as close to the experiments as possible. This approach allows us to show that spike frequency adaptation is a fundamental ingredient for the initiation process of the pulse. The introduction of a slow variable that mimics the presence of the slow K ⁺ channels in the soma and produces spike frequency adaptation increases strongly the persistence of the transient activity before the emergence of the fast pulse up to temporal and spatial scales comparable with the experiments. Finally, we demonstrate that proper levels of additive white noisy currents generate such pulses spontaneously, fully reproducing the experimental results. Electronic supplementary material   The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Murine transforming growth factor-beta 2 cDNA sequence and expression in adult tissues and embryos

Murine transforming growth factor-beta 2 (TGF-beta 2) cDNAs were isolated from cDNA libraries derived from a differentiated murine embryonic carcinoma cell line, PCC3. The composite cDNA sequence is 4267 nucleotides long, including a 1217 nucleotides 5'-untranslated sequence, and encodes a murine TGF-beta 2 precursor of 414 amino acids with 96% identity to its human counterpart. Several consensus polyadenylation sequences are present in the 1807 nucleotides 3'-untranslated sequence. Five TGF-beta 2 mRNA species are observed in the developing mouse fetus and they show different patterns of expression during development. TGF-beta 2 mRNA expression was also examined in adult mouse tissues, in which four of the five RNA species were observed. TGF-beta 2 mRNAs were present in all adult mouse tissues examined, except liver, and was most abundant in placenta, the male submaxillary gland and lung. The patterns of expression suggest a physiological role for TGF-beta 2 both in embryonic development and in the maintenance of adult tissues.     

Modulation of angiogenesis by tissue inhibitor of metalloproteinase-4

Despite the importance of MMP activity in the regulation of angiogenesis, relatively little is known about the role of TIMP-4, the most recently discovered endogenous MMP inhibitor, in modulating neovascularization. It has largely been assumed that all TIMPs are capable of inhibiting angiogenesis in vivo. However, it is now widely appreciated that TIMPs-1, -2, and -3 differ significantly in their ability to modulate angiogenic processes in vitro and angiogenesis in vivo. In order to study the effect of TIMP-4 in controlling angiogenesis, we have cloned and expressed TIMP-4 in a Pichia pastoris expression system, purified it to homogeneity, and tested its ability to regulate angiogenesis in vivo and in vitro. Our studies demonstrate that TIMP-4 is an inhibitor of capillary endothelial cell migration, but not of proliferation or of angiogenesis in vivo.     

Metabolic and functional diversity of saponins,biosynthetic intermediates and semi-synthetic derivatives

Abstract

Saponins are widely distributed plant natural products with vast structural and functional diversity. They are typically composed of a hydrophobic aglycone, which is extensively decorated with functional groups prior to the addition of hydrophilic sugar moieties, to result in surface-active amphipathic compounds. The saponins are broadly classified as triterpenoids, steroids or steroidal glycoalkaloids, based on the aglycone structure from which they are derived. The saponins and their biosynthetic intermediates display a variety of biological activities of interest to the pharmaceutical, cosmetic and food sectors. Although their relevance in industrial applications has long been recognized, their role in plants is underexplored. Recent research on modulating native pathway flux in saponin biosynthesis has demonstrated the roles of saponins and their biosynthetic intermediates in plant growth and development. Here, we review the literature on the effects of these molecules on plant physiology, which collectively implicate them in plant primary processes. The industrial uses and potential of saponins are discussed with respect to structure and activity, highlighting the undoubted value of these molecules as therapeutics.     

Two-phase species–time relationships in North American land birds

The species–time relationship (STR) is a macroecological pattern describing the increase in the observed species richness with the length of time censused. Understanding STRs is important for understanding the ecological processes underlying temporal turnover and species richness. However, accurate characterization of the STR has been hampered by the influence of sampling. I analysed STRs for 521 breeding bird survey communities. I used a model of sampling effects to demonstrate that the increase in richness was not due exclusively to sampling. I estimated the time scale at which ecological processes became dominant over sampling effects using a two‐phase model combining a sampling phase and either a power function or logarithmic ecological phase. These two‐phase models performed significantly better than sampling alone and better than simple power and logarithmic functions. Most community dynamics were dominated by ecological processes over scales <5 years. This technique provides an example of a rigorous, quantitative approach to separating sampling from ecological processes.