Population genetic structure of mahogany (Swietenia macrophylla King, Meliaceae) across the Brazilian Amazon, based on variation at microsatellite loci: implications for conservation

Mahogany (Swietenia macrophylla, Meliaceae) is the most valuable and intensively exploited Neotropical tree. No information is available regarding the genetic structure of mahogany in South America, yet the region harbours most of the unlogged populations of this prized hardwood. Here we report on the genetic diversity within and the differentiation among seven natural populations separated by up to 2100 km along the southern arc of the Brazilian Amazon basin. We analysed the variation at eight microsatellite loci for 194 adult individuals. All loci were highly variable, with the number of alleles per locus ranging from 13 to 27 (mean = 18.4). High levels of genetic diversity were found for all populations at the eight loci (mean HE = 0.781, range 0.754-0.812). We found moderate but statistically significant genetic differentiation among populations considering both estimators of FST and RST, theta = 0.097 and rho = 0.147, respectively. Estimates of theta and rho were significantly greater than zero for all pairwise population comparisons. Pairwise rho-values were positively and significantly correlated with geographical distance under the isolation-by-distance model. Furthermore, four of the populations exhibited a significant inbreeding coefficient. The finding of local differentiation among Amazonian mahogany populations underscores the need for in situ conservation of multiple populations of S. macrophylla across its distribution in the Brazilian Amazon. In addition, the occurrence of microgeographical genetic differentiation at a local scale indicates the importance of maintaining populations in their diverse habitats, especially in areas with mosaics of topography and soil.     

5, 10-Methylenetetrahydrofolate reductase (MTHFR) 677 C --> T genetic polymorphism in 228 Croatian volunteers

5, 10-Methylenetetrahydrofolate Reductase (MTHFR) is one of the key enzymes in the metabolism of homocysteine, where it catalyses its remethylation. The autosomal recessive bp 677 C --> T mutation in the MTHFR gene leads to the substitution of valine for alanine. Individuals who are homozygous for this C677T mutation exhibit a decreased specific activity and increased thermolability of this enzyme. This leads to increased plasma levels of homocysteine, which is a known risk factor for atherosclerosis and various manifestations of the atherosclerotic disease. The aim of this study was to find out the distribution and frequency of this mutation in the general Croatian population. A group of 228 volunteers (175 males and 53 females) has been analyzed for the MTHFR polymorphism, which revealed the following distribution: 105 (46.05%) individuals were without mutation (C/C), 102 (44.74%) were heterozygous (C/T) and 21 (9.21%) homozygous (T/T). These findings are within the results of studies on other European populations.     

Homocysteine induces trophoblast cell death with apoptotic features

Hyperhomocysteinemia has been suggested as a possible risk factor in women suffering from habitual abortions, placental abruption or infarcts, preeclampsia, and/or intrauterine growth retardation. However, little is known about the pathogenic mechanisms underlying the action of homocysteine. The present study investigated the in vitro ability of homocysteine to affect trophoblast gonadotropin secretion and to induce cell death. In primary human trophoblast cells, homocysteine treatment (20 micromol/L) resulted in cellular flattening and enlargement, extension of pseudopodia, and cellular vacuolization. Cellular detachment, apoptosis, and necrosis were favored. With in situ nick end labeling, we investigated DNA degradation, and we used M30 CytoDEATH to selectively stain the cytoplasm of apoptotic cells. Cytochrome c release from mitochondria to the cytosol and DNA cleavage in agarose gel have been investigated. Homocysteine, but not cysteine, induced trophoblast apoptosis and significantly reduced human chorionic gonadotropin secretion. These findings suggest that trophoblast cell death might represent a pathogenic mechanism by which homocysteine may cause pregnancy complications related to placental diseases.     

Reactions of manganese porphyrins with peroxynitrite and carbonate radical anion

We have studied the reaction kinetics of ten manganese porphyrins, differing in their meso substituents, with peroxynitrite (ONOO-) and carbonate radical anion (CO3.) using stopped-flow and pulse radiolysis, respectively. Rate constants for the reactions of Mn(III) porphyrins with ONOO- ranged from 1 x 10(5) to 3.4 x 10(7) m(-1) s(-1) and correlated well with previously reported kinetic and thermodynamic data that reflect the resonance and inductive effects of the substituents on the porphyrin ring. Rate constants for the reactions of Mn(III) porphyrins with CO3. ranged from 2 x 10(8) to 1.2 x 10(9) m(-1)s(-1) at pH 相似文献   

Cyclic nucleotides promote monocyte differentiation toward a DC-SIGN+ (CD209) intermediate cell and impair differentiation into dendritic cells

Recruitment of monocytes into tissues and their differentiation into macrophages or dendritic cells (DCs) depend on the microenvironment of the inflammatory site. Although many factors affecting this process have been identified, the intracellular signaling pathways implicated are poorly understood. We found that cyclic nucleotides regulate certain steps of monocyte differentiation into DCs. Increased levels of the cyclic nucleotides, cAMP or cGMP, inhibit differentiation of CD14(+)/CD1a(low) monocytes into CD14(-)/CD1a(high) DCs. However, DC-specific ICAM-3-grabbing nonintegrin (CD209) up-regulation was not affected by cyclic nucleotides, indicating that DC development was not blocked at the monocyte stage. Interestingly, Ag-presenting function was increased by cyclic nucleotides, as measured by the higher expression of MHC class II, CD86, and an increased ability to stimulate CD4(+) T cell proliferation in allogeneic MLRs. Although cyclic nucleotides do not completely block DC differentiation, they do block the ability of DCs to be induced to mature by LPS. Treatment during DC differentiation with either cAMP or cGMP analogues hampered LPS-induced expression of CD83, DC-LAMP, and CCR7 and the ability of DCs to migrate toward CCL19/macrophage-inflammatory protein 3beta. Interestingly, the induction of a CD16(+) subpopulation of cells was also observed. Thus, signals causing an increase in either cAMP or cGMP levels during monocyte recruitment to inflammatory sites may restrain the activation of acquired immunity by blocking DC development and migration to lymph nodes. At the same time, these signals promote development of an active intermediate cell type having properties between those of macrophages and DCs, which might contribute to the innate immune response in the periphery.     

Cytoplasmic N-terminal protein acetylation is required for efficient photosynthesis in Arabidopsis

The Arabidopsis atmak3-1 mutant was identified on the basis of a decreased effective quantum yield of photosystem II. In atmak3-1, the synthesis of the plastome-encoded photosystem II core proteins D1 and CP47 is affected, resulting in a decrease in the abundance of thylakoid multiprotein complexes. DNA array-based mRNA analysis indicated that extraplastid functions also are altered. The mutation responsible was localized to AtMAK3, which encodes a homolog of the yeast protein Mak3p. In yeast, Mak3p, together with Mak10p and Mak31p, forms the N-terminal acetyltransferase complex C (NatC). The cytoplasmic AtMAK3 protein can functionally replace Mak3p, Mak10p, and Mak31p in acetylating N termini of endogenous proteins and the L-A virus Gag protein. This result, together with the finding that knockout of the Arabidopsis MAK10 homolog does not result in obvious physiological effects, indicates that AtMAK3 function does not require NatC complex formation, as it does in yeast. We suggest that N-acetylation of certain chloroplast precursor protein(s) is necessary for the efficient accumulation of the mature protein(s) in chloroplasts.     

Influence of anatomical,physical, and detection-system parameters on surface EMG

 Many previous studies were focused on the influence of anatomical, physical, and detection-system parameters on recorded surface EMG signals. Most of them were conducted by simulations. Previous EMG models have been limited by simplifications which did not allow simulation of several aspects of the EMG generation and detection systems. We recently proposed a model for fast and accurate simulation of the surface EMG. It characterizes the volume conductor as a non-homogeneous and anisotropic medium, and allows simulation of EMG signals generated by finite-length fibers without approximation of the current-density source. The influence of thickness of the subcutaneous tissue layers, fiber inclination, fiber depth, electrode size and shape, spatial filter transfer function, interelectrode distance, length of the fibers on surface, single-fiber action-potential amplitude, frequency content, and estimated conduction velocity are investigated in this paper. Implications of the results on electrode positioning procedures, spatial filter design, and EMG signal interpretation are discussed. Received: 23 August 2000 / Accepted in revised form: 18 December 2001     

Structure--activity relationships among novel phenoxybenzamine-related beta-chloroethylamines

A series of beta-chloroethylamines 5--18, structurally related to the irreversible alpha(1)-adrenoceptor antagonist phenoxybenzamine [PB, N-benzyl-N-(2-chloroethyl)-N-(1-methyl-2-phenoxyethyl)amine hydrochloride, 1] and the competitive antagonist WB4101 [N-(2,3-dihydro-1,4-benzodioxin-2-ylmethyl)-N-[2-(2,6-dimethoxyphenoxy)ethyl]amine hydrochloride, 2], were synthesized and evaluated for their activity at alpha-adrenoceptors of the epididymal and the prostatic portion of young CD rat vas deferens. All compounds displayed irreversible antagonist activity. Most of them showed similar antagonism at both alpha(1)- and alpha(2)-adrenoceptors, whereas compounds 13 and 18, lacking substituents on both the phenoxy group and the oxyamino carbon chain, displayed a moderate alpha(1)-adrenoceptor selectivity (10--35 times), which was comparable to that of PB. Compounds 14 and 15, belonging to the benzyl series and bearing, respectively, a 2-ethoxyphenoxy and a 2-i-propoxyphenoxy moiety, were the most potent alpha(1)-adrenoceptor antagonists with an affinity value similar to that of PB (pIC(50) values of 7.17 and 7.06 versus 7.27). Interestingly, several compounds were able to distinguish two alpha(1)-adrenoceptor subtypes in the epididymal tissue, as revealed by the discontinuity of their inhibition curves. A mean ratio of 24:76 for these alpha(1)-adrenoceptors was determined from compounds 8--10, 12, and 15--17. Furthermore, compounds 9, 10, 12, 16a, and 16b showed higher affinity towards the minor population of receptors, whereas compounds 8, 15, and 17 preferentially inhibited the major population of alpha(1)-adrenoceptors. In addition, selected pharmacological experiments demonstrated the complementary antagonism of the two series of compounds and their different, preferential affinity for one of the two alpha(1)-adrenoceptor subtypes. In conclusion, we found beta-chloroethylamines that demonstrate a multiplicity of alpha(1)-adrenoceptors in the epididymal portion of young CD rat vas deferens and, as a consequence, they are possible useful tools for alpha(1)-adrenoceptor characterization.     

On the analysis of hand synergies during grasping in weightlessness

The aim of this paper was to analyse how the strategies implemented by the Central Nervous System to control the hand during grasping are modified under microgravity conditions. Two right-handed subjects carried out simple grasping tasks during parabolic flights. The trajectories of the fingers of the hand were recorded using a sensorised glove and processed in order to extract a variable (here indicated as K) which can indicated the degree of synergies existing among the fingers. The results showed that K was quite small during the trial at 1g while becoming significantly greater than 1 during the first parabolas. Then, the value k decreased to the values at 1 g after some parabolas. These results suggested a possible adaptation process of the manipulation abilities during the permanence at 0g conditions. Future extensive trials will be performed in order to confirm these preliminary results.