Role of Notch pathway in terminal follicle cell differentiation during Drosophila oogenesis

 During Drosophila oogenesis the body axes are determined by signaling between the oocyte and the somatic follicle cells that surround the egg chamber. A key event in the establishment of oocyte anterior-posterior polarity is the differential patterning of the follicle cell epithelium along the anterior-posterior axis. Both the Notch and epithelial growth factor (EGF) receptor pathways are required for this patterning. To understand how these pathways act in the process we have analyzed markers for anterior and posterior follicle cells accompanying constitutive activation of the EGF receptor, loss of Notch function, and ectopic expression of Delta. We find that a constitutively active EGF receptor can induce posterior fate in anterior but not in lateral follicle cells, showing that the EGF receptor pathway can act only on predetermined terminal cells. Furthermore, Notch function is required at both termini for appropriate expression of anterior and posterior markers, while loss of both the EGF receptor and Notch pathways mimic the Notch loss-of-function phenotype. Ectopic expression of the Notch ligand, Delta, disturbs EGF receptor dependent posterior follicle cell differentiation and anterior-posterior polarity of the oocyte. Our data are consistent with a model in which the Notch pathway is required for early follicle cell differentiation at both termini, but is then repressed at the posterior for proper determination of the posterior follicle cells by the EGF receptor pathway. Received: 5 November 1998 / Accepted: 14 December 1998     

A second generation snp-derived Escherichia coli-Streptomyces shuttle expression vector that is generally transferable by conjugation

An Escherichia coli-Streptomyces shuttle vector (pJN100) was constructed, by inserting an origin of transfer (oriT), derived from the E. coli broad host range plasmid RK2, into pANT1202, a high-copy-number vector for gene expression in Streptomyces. The resulting conjugably transferable vector contains the pANT1202-derived SnpR (LysR-like protein) activated snpA promoter that drives strong heterologous expression of proteins. We initially demonstrated that plasmid pJN100 was transferred with high frequency (10(-5-7) exconjugants per recipient) into several Streptomyces strains that were refractory to transformation by other means. Plasmid pJN100 was also shown to be stable in E. coli and Streptomyces. We confirmed functional protein expression by using a pJN100 derivative to complement a mutant of Streptomyces griseus with a disrupted chromosomal copy of the gene nonM, a gene encoding an essential reductase in the nonactin biosynthesis gene cluster. High levels of protein expression were confirmed using Western blotting to assess the production of the serine esterase NonR, an enzyme responsible for nonactin resistance in the nonactin producer S. griseus.     

Diet Is Critical for Prolonged Glycemic Control after Short-Term Insulin Treatment in High-Fat Diet-Induced Type 2 Diabetic Male Mice

Background

Clinical studies suggest that short-term insulin treatment in new-onset type 2 diabetes (T2DM) can promote prolonged glycemic control. The purpose of this study was to establish an animal model to examine such a “legacy” effect of early insulin therapy (EIT) in long-term glycemic control in new-onset T2DM. The objective of the study was to investigate the role of diet following onset of diabetes in the favorable outcomes of EIT.

Methodology

As such, C57BL6/J male mice were fed a high-fat diet (HFD) for 21 weeks to induce diabetes and then received 4 weeks of daily insulin glargine or sham subcutaneous injections. Subsequently, mice were either kept on the HFD or switched to a low-fat diet (LFD) for 4 additional weeks.

Principal Findings

Mice fed a HFD gained significant fat mass and displayed increased leptin levels, increasing insulin resistance (poor HOMA-IR) and worse glucose tolerance test (GTT) performance in comparison to mice fed a LFD, as expected. Insulin-treated diabetic mice but maintained on the HFD demonstrated even greater weight gain and insulin resistance compared to sham-treated mice. However, insulin-treated mice switched to the LFD exhibited a better HOMA-IR compared to those mice left on a HFD. Further, between the insulin-treated and sham control mice, in spite of similar HOMA-IR values, the insulin-treated mice switched to a LFD following insulin therapy did demonstrate significantly better HOMA-B% values than sham control and insulin-treated HFD mice.

Conclusion/Interpretation

Early insulin treatment in HFD-induced T2DM in C57BL6/J mice was only beneficial in animals that were switched to a LFD after insulin treatment which may explain why a similar legacy effect in humans is achieved clinically in only a portion of cases studied, emphasizing a vital role for diet adherence in diabetes control.     

Immobilization of organophosphohydrolase OpdA from Agrobacterium radiobacter by overproduction at the surface of polyester inclusions inside engineered Escherichia coli

Organophosphorus pesticides (OP) are highly toxic and are widely used as insecticides. Bacterial organophosphohydrolases which hydrolyze a variety of OPs have been considered for the clean-up of polluted environments. This study describes the engineering of Escherichia coli towards the overproduction of the organophosphohydrolase (OpdA) from Agrobacterium radiobacter at the surface of polyester inclusions. The OpdA was N-terminally fused via a designed linker region to the C-terminus of polyester inclusion-forming enzyme PhaC of Ralstonia eutropha. The PhaC-L-OpdA fusion protein was overproduced by using the strong T7 promoter and when coexpressed with genes phaA (encoding β-ketothiolase) and phaB (encoding acetoacetyl-CoA reductase) from R. eutropha this led to formation of polyester inclusions abundantly displaying OpdA. These OpdA beads showed organophosphohydrolase activity of 1,840 U/g wet polyester beads or 4,412 U/g protein. Steady state kinetics revealed that when compared with free OpdA the k(cat) (s(-1)) of 139 of immobilized OpdA was reduced by about 16.5-fold while the K(M) (M) of 2.5 × 10(-4) was increased by 1.6-fold. The immobilized OpdA showed increased temperature stability. Moreover, the stability of OpdA immobilized to polyester beads was assessed by incubating OpdA beads at 25°C for up to 11 days and no significant loss in enzyme activity was detected. The application performance of the OpdA beads with respect to hydrolysis of OPs in contaminated environments was demonstrated in wool scour spiked with fluorescent coumaphos. This study demonstrated a new strategy toward the efficient recombinant production of immobilized organophosphohydrolase, the OpdA, suitable for bioremediation applications.     

Herbivore damage along a latitudinal gradient: relative impacts of different feeding guilds

We present the first broad-scale test for a latitudinal gradient in herbivory made with consistent methods, in similar habitat type, over the entire lifespan of leaves (phyllodes). We assessed the degree of chewing, sap-sucking and mining herbivory on Acacia falcata along its entire coastal latitudinal range (1150 km) in Australia. We found no significant differences in the rate of herbivory among latitudes. Mature phyllodes had a higher rate of herbivory compared to young phyllodes, and mining was higher on mature phyllodes from the most tropical latitude. We found significant differences in phyllode toughness and specific leaf (phyllode) area among latitudes, but no significant differences among latitudes in carbon: nitrogen. This study provides a useful model for further testing of the generalisation that herbivory is more intense in tropical versus temperate regions.     

Mycorrhizal preference promotes habitat invasion by a native Australian orchid: Microtis media

Background and Aims

Mycorrhizal specialization has been shown to limit recruitment capacity in orchids, but an increasing number of orchids are being documented as invasive or weed-like. The reasons for this proliferation were examined by investigating mycorrhizal fungi and edaphic correlates of Microtis media, an Australian terrestrial orchid that is an aggressive ecosystem and horticultural weed.

Methods

Molecular identification of fungi cultivated from M. media pelotons, symbiotic in vitro M. media seed germination assays, ex situ fungal baiting of M. media and co-occurring orchid taxa (Caladenia arenicola, Pterostylis sanguinea and Diuris magnifica) and soil physical and chemical analyses were undertaken.

Key Results

It was found that: (1) M. media associates with a broad taxonomic spectrum of mycobionts including Piriformospora indica, Sebacina vermifera, Tulasnella calospora and Ceratobasidium sp.; (2) germination efficacy of mycorrhizal isolates was greater for fungi isolated from plants in disturbed than in natural habitats; (3) a higher percentage of M. media seeds germinate than D. magnifica, P. sanguinea or C. arenicola seeds when incubated with soil from M. media roots; and (4) M. media–mycorrhizal fungal associations show an unusual breadth of habitat tolerance, especially for soil phosphorus (P) fertility.

Conclusions

The findings in M. media support the idea that invasive terrestrial orchids may associate with a diversity of fungi that are widespread and common, enhance seed germination in the host plant but not co-occurring orchid species and tolerate a range of habitats. These traits may provide the weedy orchid with a competitive advantage over co-occurring orchid species. If so, invasive orchids are likely to become more broadly distributed and increasingly colonize novel habitats.     

Consistent and variable leaf anatomical characters in Carex (Cyperaceae)

The anatomy and morphology of leaves in Carex have the potential to be taxonomically useful. However, studies on the variability of leaf characteristics in the genus are sparse. Researchers therefore risk using leaf anatomical characters without the knowledge of whether they are consistent in a species. We examined 22 qualitative and seven quantitative leaf anatomy characters from transverse leaf sections to test their consistency across 11 Carex spp. The characters were clearly described and primarily microscopic. Some characters were found to exhibit high levels of intraspecific variation, whereas other characters exhibited high levels of consistency in a species, including the shape of the leaf section, the density of papillae and the size of epidermal cells. Caution must be applied when choosing leaf anatomy to delimit taxa because of the intraspecific variability found in some characters, but sufficient numbers of invariant characters exist to provide useful taxonomic separation. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 371–384.