Summary Epidermal septate junctions of Nereis sp. and Cirriformia sp. fixed with OsO4 or glutaraldehyde/OsO4 display variable structure in electron micrographs. In transverse section the septa are often indistinct and obscured by opaque material that fills the junctional cleft. Septa (spaced at 180–280 Å) are more clearly defined in slightly oblique transverse section; they exhibit an electron lucent center and appear to be linked by arms. En face views of the junction show a honeycomb pattern. Cytoplasmic faces of junctional membranes are backed with plaques opposite the septa. Lanthanum used as a tracer delineates junctional structure in negative contrast. In transverse section a chain-like lattice is present in the junctional cleft. En face views show parallel rows of pleated elements often linked by arms into honeycomb arrays. Oblique sections demonstrate that these pleated elements are continuous with the chain-like lattice seen in transverse sections. Lanthanum does not pass entirely through the junction. Lanthanum reveals that the septa have a very intricate substructure, but it is difficult to visualize the architecture that could generate the various images presented by these junctions when seen in different orientations. However, it is clear that these junctions possess some features that are diagnostic of several supposedly different types of septate junctions in invertebrates.Supported by USPHS grants NIH 5 P01 NS-07512, NIH 2701 GM-00102, and NB-00840, and by a grant from the Pomona College Research CommitteeI thank Sarah Wurzelmann, Stanley Brown, Nancy Kelly, and Gerhard Ott for excellent technical assistance. Portions of this study were carried out while I was a Postdoctoral Fellow in the Department of Anatomy, Albert Einstein College of Medicine. I dedicate this article to Berta Scharrer as a token of appreciation and affection for her guidance, encouragement, inspiration, and example of excellence 相似文献
The growth of Chinese hamster somatic cells was inhibited by 0.2 mg/cc of 2-deoxygalactose. Mutants partially or fully resistant to 2-deoxygalactose were isolated in a single-step or two-step selection. Some of them did not grow as well as the wild type; one of them which lacked galactokinase(EC.2.7.1.6) activity did not grow at all in galactose medium. The galactokinase kinetic properties (Vmax & kmax of the other mutants and of the wild type were different. Therefore resistance resulted either from the possible absence of galactokinase synthesis or from a structural mutation, possible a missence mutation, in the galactokinase gene.- A simple diagnostic test for juvenile cataract is proposed. 相似文献
The hobo transposon is responsible for one of the three hybrid dysgenic systems that have been described in Drosophila melanogaster. Most studies on the hobo dysgenic system have been carried out using the PM system as a reference. However, these two systems differ significantly.
In particular, several studies have failed to find any correlation between the molecular structures of hobo elements, the instability of the transposon and the incidence of gonadal dysgenic (GD) sterility. On the other hand, no study
of the ability of females to permit hobo activity in their progeny when they are crossed with males harboring active hobo elements (permissivity) has yet been reported. In order to investigate the parameters involved in hobo permissivity, four E strains were studied with regard to the molecular nature of their hobo sequences and the GD sterility induced by a controlled source of hobo transposase. We show that hobo permissivity varies both within and between E strains. Moreover, permissivity decreases with age in E females. Our results
are discussed with respect to similar phenomena that have been described in relation to the reactivity of the IR dysgenic
system.
Received: 17 August 1998 / Accepted: 17 December 1998 相似文献
Fitness traits of three Drosophila simulans strains infected by endocellular bacteria belonging to the genus Wolbachia have been compared with those of replicate stocks previously cured from the infection by an antibiotic treatment. The traits measured were development time, egg-to-adult viability, egg hatch, productivity, fecundity, and the number of functional ovarioles. Individuals of the first strain were bi-infected by two Wolbachia variants, wHa and wNo. The second strain was infected by wHa, the third one by wNo. The Wolbachia studied here cause cytoplasmic incompatibility (CI), a high embryonic mortality (70% to > 90%) when an infected male is crossed with an uninfected female. Three generations after antibiotic treatment, we observed in all strains a significant drop in productivity in the cured stocks. This drop was not due to antibiotic toxicity and was associated with the loss of the Wolbachia. However the effect had disappeared in two of the three strains five generations after treatment, and could not be found in the third strain in a third measurement carried out 14 generations after treatment. The temporary nature of the productivity difference indicates that Wolbachia do not enhance productivity in infected strains. On the other hand, in all traits measured, our results show the absence of any negative effects of the Wolbachia on their host. This could be explained when considering Wolbachia evolution, as maternally transmitted parasites bear a strong selective pressure not to harm their female host. However, CI would allow the bacteria to be maintained even when harming the female. The apparent absence of deleterious effects caused by these Wolbachia might result from a trade-off, where a relatively low bacteria density would advantage the Wolbachia by suppressing any deleterious effects on the female host, at the cost of a weaker maternal transmission rate of the infection. 相似文献
Plant natural products (PNP) (e.g., secondary vegetal metabolites and their derivatives) have been a productive source of active ingredients for the pharmaceutical industry. The High Throughput Screening of Plant Natural Products (PNP-HTS) with extracts or isolated compounds has shown to be time consuming, expensive, and not as successful as expected. Recently building upon the innovative fragment-based drug discovery (FBDD) a disruptive approach was developed based on PNP. The fragment approach involves elaboration and/or isolation of weakly binding small molecules with molecular weights between 150 and 250 Da. This method is fundamentally different from HTS in almost every aspect (i.e., size of the compound library, screening methods, and optimization steps from hit to lead). Due to their nature, vegetal natural fragments have unique three-dimensional (3D) properties, high Fsp3, low aromaticity, and large chemo-diversities which represent potential opportunities for developing novel drugs. Preliminary results using vegetal natural fragments appear to be a promising and emerging field which offers valuable prospects for developing new drugs.
There is growing international interest in better managing soils to increase soil organic carbon (SOC) content to contribute to climate change mitigation, to enhance resilience to climate change and to underpin food security, through initiatives such as international ‘4p1000’ initiative and the FAO's Global assessment of SOC sequestration potential (GSOCseq) programme. Since SOC content of soils cannot be easily measured, a key barrier to implementing programmes to increase SOC at large scale, is the need for credible and reliable measurement/monitoring, reporting and verification (MRV) platforms, both for national reporting and for emissions trading. Without such platforms, investments could be considered risky. In this paper, we review methods and challenges of measuring SOC change directly in soils, before examining some recent novel developments that show promise for quantifying SOC. We describe how repeat soil surveys are used to estimate changes in SOC over time, and how long‐term experiments and space‐for‐time substitution sites can serve as sources of knowledge and can be used to test models, and as potential benchmark sites in global frameworks to estimate SOC change. We briefly consider models that can be used to simulate and project change in SOC and examine the MRV platforms for SOC change already in use in various countries/regions. In the final section, we bring together the various components described in this review, to describe a new vision for a global framework for MRV of SOC change, to support national and international initiatives seeking to effect change in the way we manage our soils. 相似文献
Wetlands Ecology and Management - In the era of global environmental change, land transformation is acknowledged as a critical subject that needs to be addressed. Even though some studies have been... 相似文献
Onion maggot (Delia antiqua) is an economically important pest of Allium crops in temperate regions throughout the world. Management of this pest is necessary to achieve economic returns and depends on insecticide regimes and cultural management. Current cultural management especially altering planting date, field location and crop rotation depend on monitoring. We evaluated the effect of shape, size, colour and chemical attractants on trap catch of field populations of adult D. antiqua flies in upstate New York. White, large diameter, spherical traps in conjunction with Delia Lure attractant performed the best in attracting and catching D. antiqua adults. These results suggest an improved means of attracting and capturing D. antiqua populations which could be useful in monitoring efforts and development of attract and kill strategies for pest control. 相似文献