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71.
Clonal plant species have been shown to adopt different strategies to persist in heterogeneous environments by changing relative investments in sexual reproduction and clonal propagation. As a result, clonal diversity and genetic variation may be different along environmental gradients. We examined the regional and local population structure of the clonal rhizomatous forest herb Paris quadrifolia in a complex of forest fragments in Voeren (Belgium). Relationships between population size (the number of shoots), shoot density (the number of shoots per m2) and local growth conditions were investigated for 47 populations. Clonal diversity and genetic variation within and among 19 populations were investigated using amplified fragment length polymorphism markers. To assess the importance of sexual reproduction, seed set, seed weight and germination success were determined in 18 populations. As predicted, local growth conditions largely affected population distribution, size and density of P. quadrifolia. Populations occurring in moist and relatively productive sites contained significantly more shoots. Here, shoots were also much more sparsely distributed compared to populations occurring in dry and relatively unproductive sites, where shoots showed a strongly aggregated distribution pattern. Clonal diversity was relatively high, compared with other clonal species (G/N ratio = 0.43 and Simpson’s D=0.81). Clonal diversity significantly (P<0.01) decreased with increasing shoot density while molecular genetic variation was significantly (P<0.01) affected by population size and local environmental conditions. Lack of recruitment and out-competition of less-adapted genotypes may explain the decreased genetic variation in dry sites. Analysis of molecular variance revealed significant genetic variation among populations (Φ
ST=0.42, P<0.001), whereas pairwise genetic distances were not correlated to geographic distances, suggesting that gene flow among populations is limited. Finally, the number of generative shoots, the number of seeds per fruit and seed weight were significantly and positively related to population size and local growth conditions. We conclude that under stressful conditions populations of clonal forest plant species can slowly evolve into remnant populations characterized by low levels of genetic variation and limited sexual reproduction. Conservation of suitable habitat conditions is therefore a prerequisite for effective long-term conservation of clonal forest plant species. 相似文献
72.
Nijhof JG Braun KM Giangreco A van Pelt C Kawamoto H Boyd RL Willemze R Mullenders LH Watt FM de Gruijl FR van Ewijk W 《Development (Cambridge, England)》2006,133(15):3027-3037
We describe a novel murine progenitor cell population localised to a previously uncharacterised region between sebaceous glands and the hair follicle bulge, defined by its reactivity to the thymic epithelial progenitor cell marker MTS24. MTS24 labels a membrane-bound antigen present during the early stages of hair follicle development and in adult mice. MTS24 co-localises with expression of alpha6-integrin and keratin 14, indicating that these cells include basal keratinocytes. This novel population does not express the bulge-specific stem cell markers CD34 or keratin 15, and is infrequently BrdU label retaining. MTS24-positive and -negative keratinocyte populations were isolated by flow cytometry and assessed for colony-forming efficiency. MTS24-positive keratinocytes exhibited a two-fold increase in colony formation and colony size compared to MTS24-negative basal keratinocytes. In addition, both the MTS24-positive and CD34-positive subpopulations were capable of producing secondary colonies after serial passage of individual cell clones. Finally, gene expression profiles of MTS24 and CD34 subpopulations were compared. These results showed that the overall gene expression profile of MTS24-positive cells resembles the pattern previously reported in bulge stem cells. Taken together, these data suggest that the cell-surface marker MTS24 identifies a new reservoir of hair follicle keratinocytes with a proliferative capacity and gene expression profile suggestive of progenitor or stem cells. 相似文献
73.
Glaser S Schaft J Lubitz S Vintersten K van der Hoeven F Tufteland KR Aasland R Anastassiadis K Ang SL Stewart AF 《Development (Cambridge, England)》2006,133(8):1423-1432
Epigenesis is the process whereby the daughters of a dividing cell retain a chromatin state determined before cell division. The best-studied cases involve the inheritance of heterochromatic chromosomal domains, and little is known about specific gene regulation by epigenetic mechanisms. Recent evidence shows that epigenesis pivots on methylation of nucleosomes at histone 3 lysines 4, 9 or 27. Bioinformatics indicates that mammals have several enzymes for each of these methylations, including at least six histone 3 lysine 4 methyltransferases. To look for evidence of gene-specific epigenetic regulation in mammalian development, we examined one of these six, Mll2, using a multipurpose allele in the mouse to ascertain the loss-of-function phenotype. Loss of Mll2 slowed growth, increased apoptosis and retarded development, leading to embryonic failure before E11.5. Using chimera experiments, we demonstrated that Mll2 is cell-autonomously required. Evidence for gene-specific regulation was also observed. Although Mox1 and Hoxb1 expression patterns were correctly established, they were not maintained in the absence of Mll2, whereas Wnt1 and Otx2 were. The Mll2 loss-of-function phenotype is different from that of its sister gene Mll, and they regulate different Hox complex genes during ES cell differentiation. Therefore, these two closely related epigenetic factors play different roles in development and maintain distinct gene expression patterns. This suggests that other epigenetic factors also regulate particular patterns and that development entails networks of epigenetic specificities. 相似文献
74.
75.
Cofilin 1 is revealed as an inhibitor of glucocorticoid receptor by analysis of hormone-resistant cells 下载免费PDF全文
Significant knowledge about glucocorticoid signaling has accumulated, yet many aspects remain unknown. We aimed to discover novel factors involved in glucocorticoid receptor regulation that do not necessarily require direct receptor interaction. We achieved this by using a functional genetic screen: a stable cell line which cannot survive hormone treatment was engineered, randomly mutated, and selected in the presence of glucocorticoid. A hormone-resistant clone was analyzed by two-dimensional gel electrophoresis. Differentially expressed proteins were identified and tested as candidates for regulation of the glucocorticoid receptor. An unexpected candidate, cofilin 1, inhibited receptor activity. Cofilin is known to promote actin depolymerization and filament severing. Several experiments suggest that this feature of cofilin is involved in its inhibitory action. Both its actin depolymerization activity and its inhibitory action on the receptor are dependent on its phosphorylation state. Treatment of cells with a cytoskeleton-disrupting agent decreased receptor activity, as did overexpression of actin, particularly a mutant actin that does not polymerize. In addition, overexpression of cofilin and actin as well as chemical cytoskeleton disruption changed the subcellular receptor distribution and upregulated c-Jun, which could constitute the inhibitory mechanism of cofilin. In summary, cofilin represents a novel factor that can cause glucocorticoid resistance. 相似文献
76.
Inactivation of murine leukemia virus by compounds that react with the zinc finger in the viral nucleocapsid protein. 总被引:3,自引:2,他引:1 下载免费PDF全文
All retroviral nucleocapsid (NC) proteins, except those of spumaretroviruses, contain one or two copies of the conserved sequence motif C-X2-C-X4-H-X4-C. The conserved cysteine and histidine residues coordinate a zinc ion in each such motif. Rice et al. (W. G. Rice, J. G. Supko, L. Malspeis, R. W. Buckheit, Jr., D. Clanton, M. Bu, L. Graham, C. A. Schaeffer, J. A. Turpin, J. Domagala, R. Gogliotti, J. P. Bader, S. M. Halliday, L. Coren, R. C. Sowder II, L. 0. Arthur, and L. E. Henderson, Science 270:1194-1197, 1995) have described a series of compounds which inactivate human immunodeficiency virus type 1 (HIV-1) particles and oxidize the cysteine thiolates in the NC zinc finger. We have characterized the effects of three such compounds on Moloney murine leukemia virus (MuLV). We find that, as with HIV-1, the compounds inactivate cell-free MuLV particles and induce disulfide cross-linking of NC in these particles. The killed MuLV particles were found to be incapable of synthesizing full-length viral DNA upon infection of a new host cell. When MuLV particles are synthesized in the presence of one of these compounds, the normal maturational cleavage of the Gag polyprotein does not occur. The compounds have no effect on the infectivity of human foamy virus, a spumaretrovirus lacking zinc fingers in its NC protein. The resistance of foamy virus supports the hypothesis that the zinc fingers are the targets for inactivation of MuLV and HIV- I by the compounds. The absolute conservation of the zinc finger motif among oncoretroviruses and lentiviruses and the lethality of all known mutations altering the zinc-binding residues suggest that only the normal, wild-type structure can efficiently perform all of its functions. This possibility would make the zinc finger an ideal target for antiretroviral agents. 相似文献
77.
G. Raes J. Van Ginderachter Yuan Qing Liu L. Brys Kristiaan Thielemans Patrick De Baetselier Anja Geldhof 《Cancer immunology, immunotherapy : CII》1997,45(5):257-265
BW-Sp3 is a BW-5147-derived T cell lymphoma with limited immunogenicity since, despite regression of the majority of subcutaneous
tumors, an important fraction of the animals will die from metastases. In the present study, the BW-Sp3 cells were transfected
with genes encoding B7-1 or B7-2, known to be involved in the induction of T cell responses. The resulting transfectants exhibited
a reduced tumorigenicity and did not cause mortality in the syngeneic recipients. Furthermore, immunization with the B7-1
or B7-2 transfectants resulted in an increased generation of cytotoxic T lymphocytes (CTL) that lysed both the transfectants
and the wild-type BW-Sp3 cells. Since the B7 transfectants were completely rejected in syngeneic recipients and induced potent
CTL recognizing the wild-type BW-Sp3 cells, these engineered cells were considered as candidates for immunotherapy. Vaccinations
with the B7-1 or B7-2 transfectants could completely protect the animals from metastatic disease when subsequently challenged
with wild-type BW-Sp3 cells. Furthermore, immunization with the B7 transfectants could prolong the survival time of mice that
had been challenged intravenously with BW-Sp3 cells. Surprisingly, however, when these transfectants, as well as the wild-type
BW-Sp3 cells, were used for vaccination of tumor-bearing animals, the presence of the subcutaneous BW-Sp3 tumors clearly interfered
with the outcome of immunotherapy, resulting in increased malignancy, as reflected by a higher incidence of progressing tumors
and a reduced survival rate. Possible implications for immunotherapy in humans are discussed.
Received: 5 August 1997 / Accepted: 15 August 1997 相似文献
78.
Zinc and cadmium analysis in human prostate neoplasms 总被引:4,自引:0,他引:4
Magdalena Brys Agnieszka D. Nawrocka Eügeniüsz MlekoŚ Cezary Zydek Marek Foksinski Andrzej Barecki Wanda M. Krajewska 《Biological trace element research》1997,59(1-3):145-152
The objective of this study was to test the hypothesis that prostatic cancer is associated with the changes of zinc (Zn) and
cadmium (Cd) concentration. Normal prostate, benign prostatic hyperplasia (BPH), and prostatic carcinoma (PCA) were analyzed
for Zn and Cd by atomic absorption spectrometry. Cd level was measured using a graphite furnace and Zn level was measured
by flame mode. Metal content was assessed in whole tissues and in nuclear, plasma membrane, and cytosolic fractions. An increase
of Zn content in BPH, but a decrease in PCA as compared to normal tissue, was observed. Cd concentration appeared to be higher
in BPH and PCA than in normal tissue. No correlation between Zn and Cd level was found in BPH specimens obtained from the
same patients. Probability values ofp ≤0.05 were considered to indicate significant differences. Obtained results seem to support the hypothesis of Cd carcinogenicity
and preventing function of Zn in prostatic cancer. Plasma membrane fraction corresponding to lysosomal, mitochondrial, and
microsomal subcellular compartments are probably critical in Zn and Cd participation in human prostate neoplasms. 相似文献
79.
The present study is an attempt to investigate the pattern of morphological variability of the short roots of Norway spruce
(Picea abies (L.) Karst.) growing in different soils. Five root parameters – diameter, length and dry weight of the root tip,
root density (dry weight per water-saturated volume) and specific root area (absorbing area of dry weight unit) were studied
with respect to 11 soil characteristics using CANOCO RDA analysis. The investigation was conducted in seven study areas in
Estonia differing in site quality class and soil type. Ten root samples per study area were collected randomly from the forest
floor and from the 20 cm soil surface layer. Eleven soil parameters were included in the study: humus content, specific soil
surface area, field capacity, soil bulk density, pH (KCl and H2O dilution's), N and Ca concentrations, Ca/Al and C/N ratios, and the decomposition rate of fine roots (<2 mm dia.). Root
morphological characteristics most strongly related to the measured soil characteristics in the different sites were specific
root area, root density and diameter of the short roots, the means varying from 29 to 42 m2 kg−1, from 310 to 540 kg m−3 and from 0.26 to 0.32 mm, respectively; root density being most sensitive. The most favourable site and soil types resulting
in fine roots with morphological characteristics for optimizing nutrient uptake (e.g. low short root density and high specific
root area) were Umbric Luvisol (Oxalis), Dystric Gleysol (Oxalis) and Gleyic Luvisol (Hepatica). These soil types correspond
to highly productive natural forest stands of Norway spruce in Estonia. All measured soil variables explained 28% of total
variance of the root characteristics. The most important variables related to root morphology were the humus content, field
capacity and specific soil surface area.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
80.
Cadmium (Cd) pathology was studied in an insect cell line (Aedes albopictusC6/36) at the ultrastructural level. The most prominent pathological changes occurred at the level of the nucleus: chromatin clumping, indentations, filling and dilatation of the perinuclear cisternae and an increased amount of bound ribosomes were observed. In the cytoplasm, condensation and swelling of mitochondria, increase of both free and membrane-bound ribosomes, filling and dilatation of the rough endoplasmic reticulum, and increase of the lysosomal system were the most conspicuous effects. The increased content of the perinuclear and cytoplasmic cisternae was probably due to an increased protein synthesis or a disturbance of the protein export system. This picture differed clearly from the osmotically swollen electron-lucent cisternae that have been described in other pathological situations. The enhancement of the lysosomal system was paralleled by a slight but significant stimulation of the acid phosphatase activity in the sublethal Cd concentration range. In vitro experiments suggested that Cd probably acts directly on this enzyme. Abnormal medium acidification in cultures treated with low Cd levels was correlated with an increased production of lactic acid. Together with the morphological data, this suggested a Cd-induced impairment of the aerobic metabolism. 相似文献