High temporal resolution tracing of photosynthate carbon from the tree canopy to forest soil microorganisms

Half of the biological activity in forest soils is supported by recent tree photosynthate, but no study has traced in detail this flux of carbon from the canopy to soil microorganisms in the field. Using (13)CO(2), we pulse-labelled over 1.5 h a 50-m(2) patch of 4-m-tall boreal Pinus sylvestris forest in a 200-m(3) chamber. Tracer levels peaked after 24 h in soluble carbohydrates in the phloem at a height of 0.3 m, after 2-4 d in soil respiratory efflux, after 4-7 d in ectomycorrhizal roots, and after 2-4 d in soil microbial cytoplasm. Carbon in the active pool in needles, in soluble carbohydrates in phloem and in soil respiratory efflux had half-lives of 22, 17 and 35 h, respectively. Carbon in soil microbial cytoplasm had a half-life of 280 h, while the carbon in ectomycorrhizal root tips turned over much more slowly. Simultaneous labelling of the soil with (15)NH(+)(4) showed that the ectomycorrhizal roots, which were the strongest sinks for photosynthate, were also the most active sinks for soil nitrogen. These observations highlight the close temporal coupling between tree canopy photosynthesis and a significant fraction of soil activity in forests.     

Structural architecture of an RNA that competitively inhibits RNase L

Activation of RNase L endonuclease activity is part of the mammalian innate immune response to viral infection. The poliovirus RNA genome contains a sequence in its protein-coding region that can act as a competitive inhibitor of RNase L. Mutation, sequence, and functional analysis of this competitive inhibitor RNA (ciRNA) revealed that its activity depends on specific sequences, showed that a loop-loop hairpin interaction forms in the ciRNA, and suggested the presence of a loop E motif. These features lead to the hypothesis that the ciRNA's function is conferred in part by a specific three-dimensional folded RNA architecture. By using a combination of biophysical, mutational, and functional studies, we have mapped features of the three-dimensional architecture of the ciRNA in its unbound form. We show that the loop-loop interaction forms in the free ciRNA and affects the overall structure, perhaps forming long-range tertiary interactions with the loop E motif. Local tight RNA-RNA backbone packing occurs in parts of the structure, but the fold appears to be less stable than many other tightly packed RNAs. This feature may allow the ciRNA to accommodate the translocation of ribosomes and polymerase across this multifunctional region of the viral RNA but also to function as an RNase L inhibitor.     

Phylogenetically closely related pseudomonads isolated from arthropods exhibit differential insect-killing abilities and genetic variations in insecticidal factors

Strains belonging to the Pseudomonas protegens and Pseudomonas chlororaphis species are able to control soilborne plant pathogens and to kill pest insects by producing virulence factors such as toxins, chitinases, antimicrobials or two-partner secretion systems. Most insecticidal Pseudomonas described so far were isolated from roots or soil. It is unknown whether these bacteria naturally occur in arthropods and how they interact with them. Therefore, we isolated P. protegens and P. chlororaphis from various healthy insects and myriapods, roots and soil collected in an agricultural field and a neighbouring grassland. The isolates were compared for insect killing, pathogen suppression and host colonization abilities. Our results indicate that neither the origin of isolation nor the phylogenetic position mirror the degree of insecticidal activity. Pseudomonas protegens strains appeared homogeneous regarding phylogeny, biocontrol and insecticidal capabilities, whereas P. chlororaphis strains were phylogenetically and phenotypically more heterogenous. A phenotypic and genomic analysis of five closely related P. chlororaphis isolates displaying varying levels of insecticidal activity revealed variations in genes encoding insecticidal factors that may account for the reduced insecticidal activity of certain isolates. Our findings point towards an adaption to insects within closely related pseudomonads and contribute to understand the ecology of insecticidal Pseudomonas.     

Zika virus persistence in the male macaque reproductive tract

Zika virus (ZIKV) is unique among mosquito-borne flaviviruses in that it is also vertically and sexually transmitted by humans. The male reproductive tract is thought to be a ZIKV reservoir; however, the reported magnitude and duration of viral persistence in male genital tissues vary widely in humans and non-human primate models. ZIKV tissue and cellular tropism and potential effects on male fertility also remain unclear. The objective of this study was to resolve these questions by analyzing archived genital tissues from 51 ZIKV-inoculated male macaques and correlating data on plasma viral kinetics, tissue tropism, and ZIKV-induced pathological changes in the reproductive tract. We hypothesized that ZIKV would persist in the male macaque genital tract for longer than there was detectable viremia, where it would localize to germ and epithelial cells and associate with lesions. We detected ZIKV RNA and infectious virus in testis, epididymis, seminal vesicle, and prostate gland. In contrast to prepubertal males, sexually mature macaques were significantly more likely to harbor persistent ZIKV RNA or infectious virus somewhere in the genital tract, with detection as late as 60 days post-inoculation. ZIKV RNA localized primarily to testicular stem cells/sperm precursors and epithelial cells, including Sertoli cells, epididymal duct epithelium, and glandular epithelia of the seminal vesicle and prostate gland. ZIKV infection was associated with microscopic evidence of inflammation in the epididymis and prostate gland of sexually mature males, pathologies that were absent in uninfected controls, which could have significant effects on male fertility. The findings from this study increase our understanding of persistent ZIKV infection which can inform risk of sexual transmission during assisted reproductive therapies as well as potential impacts on male fertility.     

Ovine luteinizing hormone. II. Effects of castration and steroid administration on the levels of uncombined subunits within the pituitary

Pituitaries were removed from rams, wethers, and wethers that received Silastic implants containing 5 alpha-dihydrotestosterone (DHT), 17 beta-estradiol (E2) or DHT + E2. After homogenization and centrifugation (100,000 X g), aliquots of the supernatants were subjected to analytical gel filtration on Sephadex G-100 Superfine to separate native ovine luteinizing hormone (oLH) from its uncombined subunits. Immunoreactive oLH and oLH subunits were quantified in the elution profiles to examine the effects of castration and gonadal steroid administration on the intracellular levels of uncombined oLH subunits. Pituitaries from rams contained 1.41 +/- 0.26, 0.191 +/- 0.024, and 0.0246 +/- 0.0043 micrograms oLH, oLH alpha and oLH beta per mg tissue, respectively, which translated to oLH alpha/oLH and oLH beta/oLH molar ratios of approximately equal to 0.29 and approximately equal to 0.04. Castration decreased the concentrations of oLH and its subunits by approximately 50%, but did not significantly alter the oLH alpha/oLH and oLH beta/oLH molar ratios. All three steroid treatments further decreased the concentrations of oLH and oLH beta. Pituitaries from DHT-implanted wethers exhibited similar oLH alpha/oLH and oLH beta/oLH molar ratios to rams and unimplanted wethers. However, in E2- or DHT + E2-implanted wethers, there was a greater reduction in the concentration of native oLH than in the uncombined subunits. Thus, both the oLH alpha/oLH and oLH beta/oLH molar ratios were significantly higher in E2- or DHT + E2-implanted wethers than in the other groups. The apparent molecular sizes of oLH or its subunits were not significantly altered by castration or steroid administration. These results suggest that DHT and E2 decrease the concentrations of uncombined oLH beta as well as native oLH in the pituitary, but do not appear to alter the apparent molecular size of either oLH or its uncombined subunits However, because the levels of uncombined subunits were not decreased to the same degree as oLH in E2-implanted wethers, estrogens may affect the process of oLH subunit combination or may result in the production of molecular forms of oLH that are easier to dissociate.     

Human mammary tumor cell proliferation: primary role of platelet-derived growth factor and possible synergism with human alpha-fetoprotein.

Human mammary medullary carcinoma cells (passages 16 to 21) were cultured for 2 days to allow for attachment, followed by 6 days of culture in either fetal calf serum, human cord blood, human amniotic fluid, or growth factors in the presence or absence of purified human alpha-fetoprotein (AFP). When growth factors were tested alone, only platelet-derived growth factor produced a significant increase in cell proliferation. Although up to 40% amniotic fluid had no effect on cell proliferation, human cord blood was two-fold more potent than fetal calf serum at similar concentrations. The addition of 10 ng/ml of platelet-derived growth factor increased the proliferative activity of human cord blood 1.5- to 2.5-fold. Ablation of endogenous AFP by affinity chromatography reduced the proliferative activity of cord blood by 75%. Similarly, the mitogenic activity of cord blood plus platelet-derived growth factor was reduced by 56% when AFP was removed. Purified AFP dose-dependently enhanced the proliferative activity of platelet-derived growth factor. This synergistic effect was specific for platelet-derived growth factor. We conclude that platelet-derived growth factor is a major growth factor controlling the proliferation of these tumor cells and that AFP may enhance growth factor proliferative activity and human mammary tumor growth.     

Effects of estradiol administration in vivo on testosterone production in two populations of rat Leydig cells

Ricinus communis agglutinin, a galactose-binding lectin, agglutinates phospholipid/qlycolipid vesicles, phospholipid/glycolipid/cholesterol vesicles, low density lipoprotein, and the branched polysaccharide gum arabic. The temperature dependence of the initial velocity of agglutination is similar in all cases, with a maximum at ～25°C, and a decreased rate at lower and higher temperatures. The extent of agglutination is temperature-independent for T ≤ 25°C, and decreases with increasing temperature for T > 25°C. After agglutination at 25°C, an increase in temperature results in deagglutination. This effect is reversible upon return to 25°C. Thus RCA undergoes a reversible temperature-dependent transition between an agglutinating form (≤25°C) and a less active form (> 25°C). These observations have important consequences in the interpretation of experiments which attempt to correlate lectin-binding with temperature-dependent properties such as membrane fluidity or receptor lateral organization in natural and model membranes.