Role of platelet factors and serum complement in growth of fibroblasts with high-affinity C1q complement receptors

Summary Cultures of human diploid fibroblasts are heterogeneous in that a subpopulation interacts via high-affinity receptors with the globular head regions of the C1q complement protein. Growth and synthetic properties of these cells are characteristic of cells residing in healing wounds and inflammatory lesions. At these sites, fibroblasts are exposed to regulatory molecules such as complement components and factors released from blood platelets. We assessed the effects of native complement proteins and platelet-derived factors on proportions and phenotypic stability of high-affinity and low-affinity receptor cells generated from explants of adult and embryonic connective tissue, using radioligand binding assays and immunofluorescence analysis by flow cytometry. Fibroblasts expressing high-affinity C1q receptors could be generated from explants only when factors from platelets were present in the medium; native complement proteins were not essential. High-affinity receptor cells could be generated only from tissue; they could not be generated by incubating cultures of the low-affinity receptor phenotype in medium containing platelet-derived factors. High-affinity receptor cells, once established from explants in the presence of platelet-derived factors, persisted through many replications in the absence of platelets. We obtained the same fibroblast phenotypes from embryonic skin as from adult gingiva, but the proportion of high-affinity receptor cells from skin was much greater. We conclude that factors derived from platelets are essential for generating cultures containing fibroblasts expressing high-affinity C1q receptors, but not for their maintenance. High-affinity receptor cells may comprise a rapidly dividing subpopulation giving rise only to like progeny or to other, more differentiated cells. Supported by grants DE03301 and DE02600 from the National Institutes of Health, Bethesda, MD.     

Hypoxoside production in tissue cultures of Hypoxis rooperi

Three culture types of Hypoxis rooperi T. Moore were examined to determine whether hypoxoside was present. Of these cultures, only root-type cultures were found to contain hypoxoside. Quantification of this compound within these tissues using HPLC, indicated that malformed root (MR) cultures contained the highest levels of hypoxoside. In MR cultures initiated from corm explants, the hypoxoside content was found to fluctuate. Contrary to most reports, neither an increase in sucrose concentration in the basal medium (BM) nor light, stimulated hypoxoside synthesis within this tissue. Alternatively a lowering of the levels of inorganic nitrogen in the BM and the incubation of cultures in continuous darkness, enhanced hypoxoside production.     

Identification of two catalases in Azotobacter vinelandii: a KatG homologue and a novel bacterial cytochrome c catalase, CCCAv

Azotobacter vinelandii produces two detectable catalases during growth on minimal medium. The heat-labile catalase expressed during exponential growth phase was identified as a KatG homologue by liquid chromatography-tandem mass spectrometry (LC-MS/MS) using a mixed protein sample. The second catalase was heat resistant and had substantial residual activity after treatment at 90°C. This enzyme was purified by anion-exchange and size exclusion chromatography and was found to exhibit strong absorption at 407 nm, which is often indicative of associated heme moieties. The purified protein was fragmented by proteinase K and identified by LC-MS/MS. Some identity was shared with the MauG/bacterial cytochrome c peroxidase (BCCP) protein family, but the enzyme exhibited a strong catalase activity never before observed in this family. Because two putative c-type heme sites (CXXCH) were predicted in the peptide sequence and were demonstrated experimentally, the enzyme was designated a cytochrome c catalase (CCC_Av). However, the local organization of the CCC_Av heme motifs differed significantly from that of the BCCPs as the sites were confined to the C-terminal half of the catalase. A possible Ca²⁺ binding motif, previously described in the BCCPs, is also present in the CCC_Av peptide sequence. Some instability in the presence of EGTA was observed. Expression of the catalase was abolished in cccA mutants, resulting in a nearly 8,700-fold reduction in peroxide resistance in stationary phase.     

土壤-作物污染物迁移分配与食物安全的评价模型及其应用

人类对潜在有毒污染物的接触及其健康风险是当今环境科学与医学共同关心的热点问题,而污染土壤中毒污染物在土壤－植物系统迁移与转化是其中的关键基础问题,本文基于对现有资料的分析,提出计算污染物的环境控制标准的数学模型－污染生态模型和环境化学模型,模型计算结果表明,未污染条件下的土壤－植物间元素分配参数不符合污染土壤环境中的土壤－食用作物－人类间污染物分配的特点。因此,制定土壤环境控制标准必须考虑实施土壤的环境化学特点,本文建立的模型有其对污染物的土壤环境控制标准的计算结果,期望于对我国加强污染生态研究和食物安全评价有一定的参考意义。     

The nest predator community of grassland birds responds to agroecosystem habitat at multiple scales

Nest predation is the leading cause of reproductive failure for grassland birds of conservation concern. Understanding variation in nest predation rates is complicated by the diverse assemblage of species known to prey on nests. As part of a long‐term study of grassland bird ecology, we monitored populations of predators known to prey on grassland bird nests. We used information theoretic approach to examine the predator community's association with habitat at multiple scales, including local vegetation structure of grassland patches, spatial attributes of grassland patches (size and shape), and landscape composition surrounding grassland patches (land cover within 400 and 1600 m). Our results confirmed that nest predators respond to habitat at multiple scales and different predator species respond to habitat in different ways. The most informative habitat models we selected included variability in local vegetation (CV in the density of forbs), local patch (area and edge‐to‐interior ratio), and landscape within a 1600 m buffer around grasslands (percent of land covered by human structures and development). As a separate question, we asked if models that incorporated information from multiple scales simultaneously might improve the ability to explain variation in the predator community. Multi‐ scale models were not consistently superior to models derived from variables focused at a single spatial scale. Our results suggest that minimizing human development on and surrounding conservation land and the management of the vegetation structure on grassland fragments both may benefit grassland birds by decreasing the risk of nest predation.     

2-Amino-5-aryl-pyridines as selective CB2 agonists: Synthesis and investigation of structure–activity relationships

2-Amino-5-aryl-pyridines, exemplified by compound 1, had been identified as a synthetically tractable series of CB₂ agonists from a high-throughput screen of the GlaxoSmithKline compound collection. Described herein are the results of an investigation of the structure–activity relationships (SAR) which led to the identification a number of potent and selective agonists.     

A High Incidence of Meiotic Silencing of Unsynapsed Chromatin Is Not Associated with Substantial Pachytene Loss in Heterozygous Male Mice Carrying Multiple Simple Robertsonian Translocations

Meiosis is a complex type of cell division that involves homologous chromosome pairing, synapsis, recombination, and segregation. When any of these processes is altered, cellular checkpoints arrest meiosis progression and induce cell elimination. Meiotic impairment is particularly frequent in organisms bearing chromosomal translocations. When chromosomal translocations appear in heterozygosis, the chromosomes involved may not correctly complete synapsis, recombination, and/or segregation, thus promoting the activation of checkpoints that lead to the death of the meiocytes. In mammals and other organisms, the unsynapsed chromosomal regions are subject to a process called meiotic silencing of unsynapsed chromatin (MSUC). Different degrees of asynapsis could contribute to disturb the normal loading of MSUC proteins, interfering with autosome and sex chromosome gene expression and triggering a massive pachytene cell death. We report that in mice that are heterozygous for eight multiple simple Robertsonian translocations, most pachytene spermatocytes bear trivalents with unsynapsed regions that incorporate, in a stage-dependent manner, proteins involved in MSUC (e.g., γH2AX, ATR, ubiquitinated-H2A, SUMO-1, and XMR). These spermatocytes have a correct MSUC response and are not eliminated during pachytene and most of them proceed into diplotene. However, we found a high incidence of apoptotic spermatocytes at the metaphase stage. These results suggest that in Robertsonian heterozygous mice synapsis defects on most pachytene cells do not trigger a prophase-I checkpoint. Instead, meiotic impairment seems to mainly rely on the action of a checkpoint acting at the metaphase stage. We propose that a low stringency of the pachytene checkpoint could help to increase the chances that spermatocytes with synaptic defects will complete meiotic divisions and differentiate into viable gametes. This scenario, despite a reduction of fertility, allows the spreading of Robertsonian translocations, explaining the multitude of natural Robertsonian populations described in the mouse.