Decomposition Patterns of Foliar Litter and Deadwood in Managed and Unmanaged Stands: A 13-Year Experiment in Boreal Mixedwoods

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability.     

Familial breast/ovarian cancer and BRCA1/2 genetic screening: the role of immunohistochemistry as an additional method in the selection of patients.

Only 20-25% of families screened for BRCA1/2 mutations are found positive. Because only a positive result is informative, we studied the role of BRCA1/2 immunohistochemistry as an additional method for patient selection. From 53 high-risk-affected probands, 18 (34%) had available paraffin blocks of their tumors and were selected for this study. Mutation screening was done by conformation-sensitive gel electrophoresis and multiplex ligation-dependent probe amplification. For immunohistochemistry, 21 neoplastic specimens (15 breast carcinomas, 5 ovary neoplasms, and 1 rectal adenocarcinoma) were analyzed with BRCA1 (monoclonal antibody, Ab-1, oncogene) and BRCA2 (polyclonal antibody, Ab-2, oncogene) antibodies. Absence of the BRCA1 protein was confirmed in negative tumors by Western blotting. Seven patients were positive for BRCA1/2 mutations: 5 for BRCA1 and 2 for BRCA2. Four out of five positive patients had tumors negative for BRCA1 immunostaining, and the remaining 13 BRCA1-negative patients had positive BRCA1 immunostaining in all tumor samples. Sensitivity to predict for BRCA1 mutation carriers was 80%, and specificity was 100%, with a positive predictive value of 100% and a negative predictive value of 93%. This correlation was statistically significant (p=0.001). No correlation was observed for BRCA2. If larger studies confirm these results, high-risk patients with BRCA1-negative tumors should be screened first for this gene.     

Characterization of a monoclonal antibody to human proacrosin and its use in acrosomal status evaluation.

Among the monoclonal antibodies (MAb) selected after immunization of mice with a detergent-insoluble fraction from human spermatozoa, MAb 4D4 was found to stain in immunofluorescence the principal part of the acrosome of human spermatozoa. Acrosome reaction induced decreased and spotty 4D4 immunofluorescence staining. Immunoelectron microscopy before or after embedding revealed that the epitope defined by MAb 4D4 was sequestered in the anterior acrosomal matrix and, after the acrosome reaction, remained partly bound on matrix elements attached to the inner acrosomal membrane. Western blot analysis of sperm extracts showed that the epitope defined by MAb 4D4 was located on a 55 KD polypeptide in whole cells and on 55 and 50 KD polypeptides in non-ionic detergent fractions. Human proacrosin-enriched fraction obtained by FPLC purification exhibited several proteolytic activities against gelatin in gel enzymography: a 50 KD major band and two minor bands in the 20-30 KD area; the 50 KD polypeptide reacted with MAb 4D4 in Western blots. Furthermore, the 4D4-immunoprecipitated polypeptide from sperm extract showed that the 50 KD band exhibited proteolytic activity with an optimal pH at 8.0 that was strongly inhibited by soybean trypsin inhibitor and ZnCl2. MAb 4D4 also reacted with the acrosome of the monkey Macaca fascicularis but not with the acrosome of any of the other non-primate mammalian species examined so far. Various shape defects of the acrosomal principal region were revealed by 4D4 labeling of spermatozoa with head anomalies from infertile patients. MAb 4D4 also recognized proacrosin in paraffin-embedded human testis sections. These data make the monoclonal antiproacrosin antibody 4D4 an efficient tool for evaluation of the acrosomal status of human spermatozoa and spermatids.     

Apical Scaffolding Protein NHERF2 Modulates the Localization of Alternatively Spliced Plasma Membrane Ca2+ Pump 2B Variants in Polarized Epithelial Cells

The membrane localization of the plasma membrane Ca²⁺-ATPase isoform 2 (PMCA2) in polarized cells is determined by alternative splicing; the PMCA2w/b splice variant shows apical localization, whereas the PMCA2z/b and PMCA2x/b variants are mostly basolateral. We previously reported that PMCA2b interacts with the PDZ protein Na⁺/H⁺ exchanger regulatory factor 2 (NHERF2), but the role of this interaction for the specific membrane localization of PMCA2 is not known. Here we show that co-expression of NHERF2 greatly enhanced the apical localization of GFP-tagged PMCA2w/b in polarized Madin-Darby canine kidney cells. GFP-PMCA2z/b was also redirected to the apical membrane by NHERF2, whereas GFP-PMCA2x/b remained exclusively basolateral. In the presence of NHERF2, GFP-PMCA2w/b co-localized with the actin-binding protein ezrin even after disruption of the actin cytoskeleton by cytochalasin D or latrunculin B. Surface biotinylation and fluorescence recovery after photobleaching experiments demonstrated that NHERF2-mediated anchorage to the actin cytoskeleton reduced internalization and lateral mobility of the pump. Our results show that the specific interaction with NHERF2 enhances the apical concentration of PMCA2w/b by anchoring the pump to the apical membrane cytoskeleton. The data also suggest that the x/b splice form of PMCA2 contains a dominant lateral targeting signal, whereas the targeting and localization of the z/b form are more flexible and not fully determined by intrinsic sequence features.     

The Distribution of Coumarins and Furanocoumarins in Citrus Species Closely Matches Citrus Phylogeny and Reflects the Organization of Biosynthetic Pathways

Citrus plants are able to produce defense compounds such as coumarins and furanocoumarins to cope with herbivorous insects and pathogens. In humans, these chemical compounds are strong photosensitizers and can interact with medications, leading to the “grapefruit juice effect”. Removing coumarins and furanocoumarins from food and cosmetics imply additional costs and might alter product quality. Thus, the selection of Citrus cultivars displaying low coumarin and furanocoumarin contents constitutes a valuable alternative. In this study, we performed ultra-performance liquid chromatography coupled with mass spectrometry analyses to determine the contents of these compounds within the peel and the pulp of 61 Citrus species representative of the genetic diversity all Citrus. Generally, Citrus peel contains larger diversity and higher concentrations of coumarin/furanocoumarin than the pulp of the same fruits. According to the chemotypes found in the peel, Citrus species can be separated into 4 groups that correspond to the 4 ancestral taxa (pummelos, mandarins, citrons and papedas) and extended with their respective secondary species descendants. Three of the 4 ancestral taxa (pummelos, citrons and papedas) synthesize high amounts of these compounds, whereas mandarins appear practically devoid of them. Additionally, all ancestral taxa and their hybrids are logically organized according to the coumarin and furanocoumarin pathways described in the literature. This organization allows hypotheses to be drawn regarding the biosynthetic origin of compounds for which the biogenesis remains unresolved. Determining coumarin and furanocoumarin contents is also helpful for hypothesizing the origin of Citrus species for which the phylogeny is presently not firmly established. Finally, this work also notes favorable hybridization schemes that will lead to low coumarin and furanocoumarin contents, and we propose to select mandarins and Ichang papeda as Citrus varieties for use in creating species devoid of these toxic compounds in future breeding programs.     

Antigenic study of the differentiation of the human kidney using monoclonal antibodies

The production of monoclonal antibodies against human embryonic renal cells allowed to display on the adult human kidney some antigens typical of certain structures or tissues: the proximal convoluted tubule for EG 9-11 and EG 19-6 monoclonal antibodies, the glomerular basement membrane for EG 14-1, the urothelium for EE 24-6, the connective tissue for EK 8-1 and EK 17-1 and probably the capsular and tubular basement membranes for EK 8-1. Simultaneously, we could follow the spatial and temporal repartition of the antigens during the renal development. One of them (EI 16-1) seemed to disappear in the adult and might correspond to a foetal type-antigen.     

An Na+-stimulated Mg2+-transport system in human red blood cells

The initial rate of net Mg2+ efflux was measured in human red blood cells by atomic absorption. In fresh erythrocytes incubated in Na+,K+-Ringer's medium this rate was 7.3 +/- 2.8 mumol/l cells per h (mean +/- S.D. of 14 subjects) with an energy of activation of 13 200 cal/mol. Cells with total Mg2+ contents ([ Mg]i) ranging from 1.8 to 24 mmol/l cells were prepared by using a modified p-chloromercuribenzenesulphonate method. Mg2+ efflux was strongly stimulated by increases in [Mg]i and in external Na+ concentrations ([ Na]o). A kinetic analysis of Mg2+ efflux as a function of [Mg]i and [Na]o revealed the existence of two components: an Na+-stimulated Mg2+ efflux, which exhibited a Michaelian-like dependence of free internal Mg2+ content (apparent dissociation constant = 2.6 +/- 1.4 mmol/l cells; mean +/- S.D. of six subjects) and on external Na+ concentration (apparent dissociation constant = 20.5 +/- 1.9 mM; mean +/- S.D. of four subjects) and a variable maximal rate ranging from 35 to 370 mumol/l cells per h, and an Na+-independent Mg2+ efflux, which showed a linear dependence on internal Mg2+ content with a rate constant of (6.6 +/- 0.7) X 10(-3) h-1. Fluxes catalyzed by the Na+-stimulated Mg2+ carrier were partially dependent on the ATP content of the cells and completely inhibited by quinidine (IC50 = 50 microM) and by Mn2+ (IC50 = 0.5-1.0 mM).