The structure of symplasmic early oocytes and their enveloping sheath cells in the polychaete,Platynereis dumerilii

1. Early oocytes of Platynereis dumerilii are found in clusters floating in the coelom. The oocytes of a cluster form a syncytium which is enveloped by several sheath cells. 2. At stage 2, only a single sheath cell per cluster remains, and it penetrates the group of rounded oocytes, enveloping each one of them. At stage 4, this cell contains a reticular basket made up of bundles of filaments and is inferred to be degenerating, from the presence of vacuoles, clumps of pigment-like material, and atypical mitochondria. 3. Synaptonemal complexes are typical of the nuclei of stage 2 oocytes. Oocytes of stage 4 (early vitellogenesis) contain stacks of endoplasmic reticulum in a distinctive arrangement, with interspersed electron-dense masses. Similar masses accumulate in the cytoplasm close to the nucleus and adjacent to the nuclear pores. 4. From the present observations, a physical supporting rather than a nutritive function is attributed to the sheath cell, which ensures cohesion among the oocytes connected with each other throughout the cluster phase by cytoplasmic bridges. This finding is discussed with respect to conclusions drawn from oocyte transplantation experiments.     

Novel insights into the genetic background of genetically modified mice

Unclear or misclassified genetic background of laboratory rodents or a lack of strain awareness causes a number of difficulties in performing or reproducing scientific experiments. Until now, genetic differentiation between strains and substrains of inbred mice has been a challenge. We have developed a screening method for analyzing inbred strains regarding their genetic background. It is based on 240 highly informative short tandem repeat (STR) markers covering the 19 autosomes as well as X and Y chromosomes. Combination of analysis results for presence of known C57BL/6 substrain-specific mutations together with autosomal STR markers and the Y-chromosomal STR-haplotype provides a comprehensive snapshot of the genetic background of mice. In this study, the genetic background of 72 mouse lines obtained from 18 scientific institutions in Germany and Austria was determined. By analyzing only 3 individuals per genetically modified line it was possible to detect mixed genetic backgrounds frequently. In several lines presence of a mispairing Y chromosome was detected. At least every second genetically modified line displayed a mixed genetic background which could lead to unexpected and non-reproducible results, irrespective of the investigated gene of interest.     

Numerical investigation of bone remodelling around immediately loaded dental implants using sika deer (Cervus nippon) antlers as implant bed

This study combines finite element method and animal studies, aiming to investigate tissue remodelling processes around dental implants inserted into sika deer antler and to develop an alternative animal consuming model for studying bone remodelling around implants. Implants were inserted in the antlers and loaded immediately via a self-developed loading device. After 3, 4, 5 and 6 weeks, implants and surrounding tissue were taken out. Specimens were scanned by μCT scanner and finite element models were generated. Immediate loading and osseointegration conditions were simulated at the implant-tissue interface. A vertical force of 10 N was applied on the implant. During the healing time, density and Young’s modulus of antler tissue around the implant increased significantly. For each time point, the values of displacement, stresses and strains in the osseointegration model were lower than those of the immediate loading model. As the healing time increased, the displacement of implants was reduced. The 3-week immediate loading model (9878 ± 1965 μstrain) illustrated the highest strains in the antler tissue. Antler tissue showed similar biomechanical properties as human bone in investigating the bone remodelling around implants, therefore the use of sika deer antler model is a promising alternative in implant biomechanical studies.     

Effects of scarcity and excess of larval food on life history traits of Aedes aegypti (Diptera: Culicidae)

Few studies have assessed the effects of food scarcity or excess on the life history traits of Aedes aegypti (L.) (Diptera: Culicidae) independently from larval density. We assessed immature survival, development time, and adult size in relation to food availability. We reared cohorts of 30 Ae. aegypti larvae from newly hatched to adult emergence with different food availability. Food conditions were kept constant by transferring larvae each day to a new food solution. Immature development was completed by some individuals in all treatments. The shortest development time, the largest adults, and the highest survival were observed at intermediate food levels. The most important effects of food scarcity were an extension in development time, a decrease in the size of adults, and a slight decrease in survival, while the most important effects of food excess were an important decrease in survival and a slight decrease in the size of adults. The variability in development time and adult size within sex and treatment increased at decreasing food availability. The results suggest that although the studied population has adapted to a wide range of food availabilities, both scarcity and excess of food have important negative impacts on fitness.     

Documenting Resistance and Physiological Changes in Soybean Challenged by <Emphasis Type="Italic">Aphis glycines</Emphasis> Matsumura (Hemiptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a limiting factor in soybean production in the North Central region of the USA. The objectives of this work were to identify sources of resistance to A. glycines in 14 soybean genotypes, and also document changes in total protein, peroxidase, and chlorophyll in response to aphid feeding. A reduced number of A. glycines was observed on the genotypes UX 2569-159-2-01 and UX 2570-171- 04, indicating the presence of antixenosis and/or antibiosis. UX 2569-159-2-01 expressed the highest level of resistance; whereas, UX 2570-171-04 had moderate levels of resistance to A. glycines. Chlorophyll content was relatively unaffected by A. glycines, except for a reduction in UX 2569-159-2-01 infested plants at 5 and 15 days after infestation (DAI). No changes were detected in total protein content between infested and control plants for the genotypes analyzed; however, peroxidase activity was higher in infested UX 2570-171-04 at both 5 and 10 DAI. This improvement in peroxidase content in infested UX 2570-171-04 may be playing multiple roles in the plant tolerance.     

Conversion of aliphatic nitriles by the arylacetonitrilase from <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> EBC191

The conversion of aliphatic nitriles by the arylacetonitrilase from Pseudomonas fluorescens EBC191 (NitA) was analyzed. The nitrilase hydrolysed a wide range of aliphatic mono- and dinitriles and showed a preference for unsaturated aliphatic substrates containing 5–6 carbon atoms. In addition, increased reaction rates were also found for aliphatic nitriles carrying electron withdrawing substituents (e.g. chloro- or hydroxy-groups) close to the nitrile group. Aliphatic dinitriles were attacked only at one of the nitrile groups and with most of the tested dinitriles the monocarboxylates were detected as major products. In contrast, fumarodinitrile was converted to the monocarboxylate and the monocarboxamide in a ratio of about 65:35. Significantly different relative amounts of the two products were observed with two nitrilase variants with altered reaction specifities. NitA converted some aliphatic substrates with higher rates than 2-phenylpropionitrile, which is one of the standard substrates for arylacetonitrilases. This indicated that the traditional classification of nitrilases as “arylacetonitrilases”, “aromatic” or “aliphatic” nitrilases might require some corrections. This was also suggested by the construction of some variants of NitA which were modified in an amino acid residue which was previously suggested to be essential for the conversion of aliphatic substrates by a homologous nitrilase.