Ontogeny of murine I-Ak antigens in tissue of nonlymphoid origin

The ontogeny of I-A^k antigens in murine tissues of nonlymphoid origin has been evaluated by reacting acetone-fixed cryostat sections of embryonic, neonate, and adult tissues with the MoAb 10-2.16 in indirect immunofluorescence. Thymus dendritic cells appear to be the first to express I-A^k antigens which become detectable only after birth in skin Langerhans cells, gastrointestinal epithelium, septal cells in lung alveoli, and some endothelia. The full expression of I-A^k antigens as detected in adult mice is reached only at I month of age.     

Dynamic properties of an oriented lipid/DNA complex studied by neutron scattering

The formation of lipid-DNA (CL-DNA) complexes called lipoplexes, proposed as DNA vectors in gene therapy, is obtained by adding DNA to a solution containing liposomes composed of cationic and neutral lipids. The structural and dynamic properties of such lipoplexes are determined by a coupling between the electrostatic interactions and the elastic parameters of the lipid mixture. An attempt to achieve a better understanding of the structure-dynamics relationship is reported herein. In particular, an elastic neutron scattering investigation of DOTAP-DOPC (dioleoyl trimethylammonium propane-dioleoyl phosphatidylcoline) complexed with DNA is described. Proton dynamics in this oriented CL-DNA lipoplex is found to be strongly dependent upon DNA concentration. Our results show that a substantial modification of the membrane dynamics is accompanied by the balancing of the total net charge inside the complex, together with the consequent displacement of interlayer water molecules.     

Biotic responses buffer warming‐induced soil organic carbon loss in Arctic tundra

Climate warming can result in both abiotic (e.g., permafrost thaw) and biotic (e.g., microbial functional genes) changes in Arctic tundra. Recent research has incorporated dynamic permafrost thaw in Earth system models (ESMs) and indicates that Arctic tundra could be a significant future carbon (C) source due to the enhanced decomposition of thawed deep soil C. However, warming‐induced biotic changes may influence biologically related parameters and the consequent projections in ESMs. How model parameters associated with biotic responses will change under warming and to what extent these changes affect projected C budgets have not been carefully examined. In this study, we synthesized six data sets over 5 years from a soil warming experiment at the Eight Mile Lake, Alaska, into the Terrestrial ECOsystem (TECO) model with a probabilistic inversion approach. The TECO model used multiple soil layers to track dynamics of thawed soil under different treatments. Our results show that warming increased light use efficiency of vegetation photosynthesis but decreased baseline (i.e., environment‐corrected) turnover rates of SOC in both the fast and slow pools in comparison with those under control. Moreover, the parameter changes generally amplified over time, suggesting processes of gradual physiological acclimation and functional gene shifts of both plants and microbes. The TECO model predicted that field warming from 2009 to 2013 resulted in cumulative C losses of 224 or 87 g/m², respectively, without or with changes in those parameters. Thus, warming‐induced parameter changes reduced predicted soil C loss by 61%. Our study suggests that it is critical to incorporate biotic changes in ESMs to improve the model performance in predicting C dynamics in permafrost regions.     

Characterization of the chromosome complement of Helianthus annuus by in situ hybridization of a tandemly repeated DNA sequence.

A tandemly repeated sequence isolated from a clone (HAG004N15) of a nebulized genomic DNA library of sunflower (Helianthus annuus L., 2n = 34) was characterized and used to study the chromosome complement of sunflower. HAG004N15 repeat units (368 bp in length) were found to be highly methylated, and their copy number per haploid (1C) genome was estimated to be 7800. After in situ hybridization of HAG004N15 repeats onto chromosome spreads, signals were observed at the end of both chromosome arms in 4 pairs and at the end of only one arm in 8 other pairs. Signals were also observed at the intercalary (mostly subtelomeric) regions in all pairs, in both arms in 8 pairs, and in only one arm in the other 9 pairs. The short arm of 1 pair was labelled entirely. The chromosomal location of ribosomal DNA was also studied by hybridizing the wheat ribosomal probe pTa71. Four chromosome pairs contained ribosomal cistrons at the end of their shorter arm, but a satellite was seen in only 3 pairs. These hybridization patterns were the same in the 3 sunflower lines studied (HA89, RA20031, and HOR). The chromosomal localization of HAG004N15-related sequences allowed all of the chromosome pairs to be distinguished from each other, in spite of small size and similar morphology.     

Influence of plastic embedding media on staining and morphology of lipid bodies

Summary The following light microscopy staining techniques were applied to plastic embedded tissues: Toluidine Blue, Sudan III, Sudan Black and Nile Blue sulphate. All these procedures stain the lipid bodies; however the Sudan III appears to be the most suitable.The ultramicroscopic appearance of lipid bodies of tissues embedded in Epon, Araldite and Vestopal W is presented. The effects of dehydration as well as of different electron microscopic staining techniques is also investigated.This work was supported by Grants of Consiglio Nazionale delle Ricerche of Italy: no. 115/1151/0-1247, no. 115/0815/0-1365.The excellent technical assistance of Miss Hermina Spiele is gratefully acknowledge.     

Prey size and predator density modify impacts by natural enemies towards mosquitoes

1. Interactions between multiple predators can modify prey risk and profoundly alter ecological community dynamics. Further, ontogenic prey size changes are known to mediate prey risk through refuge effects. Understandings of these biotic factors is important for robust quantifications of natural enemy effects on target species, yet their combined influence lacks investigation. 2. Functional responses were used to quantify the predatory impacts of Notonecta glauca (water boatman; Ng) and Gammarus pulex (river shrimp; Gp) towards four different larval instars of Culex pipiens in container-style habitats. Using conspecific pairs of predators, multiple predator effects (MPEs) of both predator species were examined across larval prey sizes, and prey preference tests were applied to examine prey selectivity across predator–prey body size ratios. 3. Both predators were able to feed on C. pipiens across their larval ontogeny; however, Ng consumed significantly more larvae than Gp. Functional responses of Ng were typically Type IIs, whereas Gp trended towards sigmoidal Type IIIs. Predation by pairs of Ng and Gp showed independent MPEs towards first-, third-, and fourth-instar stages (except predation by Gp at higher densities of fourth-instar) stages, whereas, for second-instar stages, Ng showed synergistic MPEs and Gp showed antagonistic MPEs. Both predators preferred late instar mosquitoes (Ng: fourth instar; Gp: third instar). These preferences reflected predator:prey weight–length ratios, showing that relative sizes of predators and prey are important factors in prey selectivity. 4. The results obtained in the present study demonstrate that MPEs, combined with intraspecific prey preferences, may modulate trophic interactions within ecosystems. Therefore, such effects should be increasingly considered to further the understanding of agent efficacies.