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51.
Drying disturbances are the primary determinant of aquatic community biodiversity in dynamic river ecosystems. Research exploring how communities respond to disturbance has focused on benthic invertebrates in surface sediments, inadequately representing a connected community that extends into the subsurface. We compared subsurface and benthic invertebrate responses to drying, to identify common and context‐dependent spatial patterns. We characterized community composition, alpha diversity and beta diversity across a gradient of drying duration. Subsurface communities responded to drying, but these responses were typically less pronounced than those of benthic communities. Despite compositional changes and in contrast to reductions in benthic alpha diversity, the alpha diversity of subsurface communities remained stable except at long drying durations. Some primarily benthic taxa were among those whose subsurface frequency and abundance responded positively to drying. Collectively, changing composition, stable richness and taxon‐specific increases in occurrence provide evidence that subsurface sediments can support persistence of invertebrate communities during drying disturbances. Beta‐diversity patterns varied and no consistent patterns distinguished the total diversity, turnover or nestedness of subsurface compared to benthic communities. In response to increasing drying duration, beta diversity increased or remained stable for benthic communities, but remained stable or decreased for subsurface communities, likely reflecting contrasts in the influence of mass effects, priority effects and environmental filtering. Dissimilarity between subsurface and benthic communities remained stable or increased with drying duration, suggesting that subsurface communities maintain distinct biodiversity value while also supporting temporary influxes of benthic taxa during drying events. As temporary rivers increase in extent due to global change, we highlight that recognizing the connected communities that extend into the subsurface sediments can enable holistic understanding of ecological responses to drying, the key determinant of biodiversity in these dynamic ecosystems. 相似文献
52.
Endocrine control of follicular growth was determined by observing the left ovary of prepubertal calves previously treated with a potent GnRH agonist for 13 days. The ovarian response to hormonal stimulation was determined using the right ovaries of the same animals. Three-month-old crossbred calves were assigned to one of the two following treatment groups: 1) saline control for 13 days, with purified porcine FSH for the last 3 days (n = 5); and 2) GnRHa for 13 days, with purified porcine FSH for the final 3 days (n = 5). The left ovaries were removed from all calves after 10 days, and the right ovaries were removed at the end of treatment. Plasma concentrations of FSH, LH and oestradiol-17 beta were followed up during the GnRHa and pFSH treatments. The maximum macroscopic diameter of the F1 follicle, as determined by daily ultrasonography, did not differ between GnRHa-treated calves (from 6.6 to 10.4 mm) and the saline control calves (from 6.7 to 10.3 mm). Histological analysis of the ovaries showed that the number of follicles > 0.40 mm in diameter varied greatly for calves of the two groups (from 11 to 220 at 10 days). GnRHa significantly increased the mean number of follicles (total and nonatretic) of size class > 5.4 mm as compared to saline control calves (P < 0.05). The FSH treatment significantly increased the mean number of follicles 3.00-5.4 and > 5.4 mm in diameter (P < 0.05), with no change in the number of follicles smaller than 3.00 mm. The rate of atresia of large follicles (3.01-5.40 mm) was significantly reduced by purified porcine FSH treatment in both groups (P < 0.05). In no case did the GnRHa induce ovulation or luteinization of follicles. The LH and FSH concentrations increased transiently after GnRHa treatment on the first day, but afterwards, both hormones increased to only one sixth of what was observed after the initial GnRHa injection treatment. This increase in LH and FSH was observed 1 h after GnRHa treatment on each consecutive day of the experiment and were significantly different in the control group (0 h versus 1 h versus 2 h x saline control versus GnRH agonists groups; P < 0.01). During the superovulatory treatment, FSH concentrations peaked at around 0.70 ng.mL-1 in both saline- and GnRHa-treated groups on the first day but on the last day of surovulatory treatment, FSH concentrations were higher in GnRHa agonist-treated calves than in the control calves (day 11 versus day 12 versus day 13 x saline control versus GnRH agonist treatment groups; P < 0.01). LH profiles were unchanged by surovulatory treatment. Concentrations of oestradiol-17 beta increased significantly over the three days (P < 0.001) of the superovulatory treatments in both groups (P < 0.01). These results indicate that GnRH agonist treatment allows recruited antral follicles to pursue their growth during the early selection process via sustained FSH and LH secretion allowing more than a single large follicle to maintain their growth without going to atresia. 相似文献
53.
Duc R Leong-Morgenthaler PM 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2004,802(1):183-187
Heterocyclic amines, found ubiquitously in our diet, are carcinogenic and mutagenic. Among this class of compounds, 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP) is the most abundant. To further understand the carcinogenesis of this compound, we studied the effects of PhIP on the progression of human lymphoblastoid cells through the cell-cycle. Cells differing in p53 or mismatch repair status were used to evaluate the role of those proteins. Following PhIP-treatment, a dose and time-dependent accumulation of p53 was found in cells containing functional p53. The augmentation of the p53 protein, accompanied by increases in p21-WAF1, confirms that the p53 is activated. The increase in p53 was independent of the mismatch repair status of the cells. Perturbations in the cell-cycle were also observed. Twenty-four hours after PhIP treatment, the activation of the G2-M checkpoint was evident. Functional p53 and mismatch repair were not required for the PhIP-induced G2-M arrest. The G2-M arrests were reversible and are interpreted as necessary for the repair of the PhIP-DNA lesions. Under treatment conditions where less than 5% of the cells survived, the G2-M arrests were absent. 相似文献
54.
Comparative RFLP mapping has revealed extensive conservation of marker order in different grass genomes. However, microcolinearity studies at the sequence level have shown rapid genome evolution and many exceptions to colinearity. Most of these studies have focused on a limited size of genomic fragment and the extent of microcolinearity over large distances or across entire genomes remains poorly characterized in grasses. Here, we have investigated the microcolinearity between the rice genome and a total of 1,500 kb from physical BAC contigs on wheat chromosome 1AS. Using ESTs mapped in wheat chromosome bins as an additional source of physical data, we have identified 27 conserved orthologous sequences between wheat chromosome 1AS and a region of 1,210 kb located on rice chromosome 5S. Our results extend the orthology described earlier between wheat chromosome group 1S and rice chromosome 5S. Microcolinearity was found to be frequently disrupted by rearrangements which must have occurred after the divergence of wheat and rice. At the Lr10 orthologous loci, microrearrangements were due to the insertion of mobile elements, but also originated from gene movement, amplification, deletion and inversion. These mechanisms of genome evolution are at the origin of the mosaic conservation observed between the orthologous regions. Finally, in silico mapping of wheat genes identified an intragenomic colinearity between fragments from rice chromosome 1L and 5S, suggesting an ancestral segmental duplication in rice.Electronic Supplementary Material Supplementary material is available in the online version of this article at 相似文献
55.
Large-scale exploration of growth inhibition caused by overexpression of genomic fragments in Saccharomyces cerevisiae 下载免费PDF全文
Boyer J Badis G Fairhead C Talla E Hantraye F Fabre E Fischer G Hennequin C Koszul R Lafontaine I Ozier-Kalogeropoulos O Ricchetti M Richard GF Thierry A Dujon B 《Genome biology》2004,5(9):R72-19
We have screened the genome of Saccharomyces cerevisiae for fragments that confer a growth-retardation phenotype when overexpressed in a multicopy plasmid with a tetracycline-regulatable (Tet-off) promoter. We selected 714 such fragments with a mean size of 700 base-pairs out of around 84,000 clones tested. These include 493 in-frame open reading frame fragments corresponding to 454 distinct genes (of which 91 are of unknown function), and 162 out-of-frame, antisense and intergenic genomic fragments, representing the largest collection of toxic inserts published so far in yeast. 相似文献
56.
Rapid genome divergence at orthologous low molecular weight glutenin loci of the A and Am genomes of wheat 总被引:19,自引:0,他引:19 下载免费PDF全文
Wicker T Yahiaoui N Guyot R Schlagenhauf E Liu ZD Dubcovsky J Keller B 《The Plant cell》2003,15(5):1186-1197
To study genome evolution in wheat, we have sequenced and compared two large physical contigs of 285 and 142 kb covering orthologous low molecular weight (LMW) glutenin loci on chromosome 1AS of a diploid wheat species (Triticum monococcum subsp monococcum) and a tetraploid wheat species (Triticum turgidum subsp durum). Sequence conservation between the two species was restricted to small regions containing the orthologous LMW glutenin genes, whereas >90% of the compared sequences were not conserved. Dramatic sequence rearrangements occurred in the regions rich in repetitive elements. Dating of long terminal repeat retrotransposon insertions revealed different insertion events occurring during the last 5.5 million years in both species. These insertions are partially responsible for the lack of homology between the intergenic regions. In addition, the gene space was conserved only partially, because different predicted genes were identified on both contigs. Duplications and deletions of large fragments that might be attributable to illegitimate recombination also have contributed to the differentiation of this region in both species. The striking differences in the intergenic landscape between the A and A(m) genomes that diverged 1 to 3 million years ago provide evidence for a dynamic and rapid genome evolution in wheat species. 相似文献
57.
Chazaud B Sonnet C Lafuste P Bassez G Rimaniol AC Poron F Authier FJ Dreyfus PA Gherardi RK 《The Journal of cell biology》2003,163(5):1133-1143
Once escaped from the quiescence niche, precursor cells interact with stromal components that support their survival, proliferation, and differentiation. We examined interplays between human myogenic precursor cells (mpc) and monocyte/macrophages (MP), the main stromal cell type observed at site of muscle regeneration. mpc selectively and specifically attracted monocytes in vitro after their release from quiescence, chemotaxis declining with differentiation. A DNA macroarray-based strategy identified five chemotactic factors accounting for 77% of chemotaxis: MP-derived chemokine, monocyte chemoattractant protein-1, fractalkine, VEGF, and the urokinase system. MP showed lower constitutive chemotactic activity than mpc, but attracted monocytes much strongly than mpc upon cross-stimulation, suggesting mpc-induced and predominantly MP-supported amplification of monocyte recruitment. Determination of [3H]thymidine incorporation, oligosomal DNA levels and annexin-V binding showed that MP stimulate mpc proliferation by soluble factors, and rescue mpc from apoptosis by direct contacts. We conclude that once activated, mpc, which are located close by capillaries, initiate monocyte recruitment and interplay with MP to amplify chemotaxis and enhance muscle growth. 相似文献
58.
Capillary malformation-arteriovenous malformation, a new clinical and genetic disorder caused by RASA1 mutations 总被引:6,自引:0,他引:6 下载免费PDF全文
Eerola I Boon LM Mulliken JB Burrows PE Dompmartin A Watanabe S Vanwijck R Vikkula M 《American journal of human genetics》2003,73(6):1240-1249
Capillary malformation (CM), or "port-wine stain," is a common cutaneous vascular anomaly that initially appears as a red macular stain that darkens over years. CM also occurs in several combined vascular anomalies that exhibit hypertrophy, such as Sturge-Weber syndrome, Klippel-Trenaunay syndrome, and Parkes Weber syndrome. Occasional familial segregation of CM suggests that there is genetic susceptibility, underscored by the identification of a large locus, CMC1, on chromosome 5q. We used genetic fine mapping with polymorphic markers to reduce the size of the CMC1 locus. A positional candidate gene, RASA1, encoding p120-RasGAP, was screened for mutations in 17 families. Heterozygous inactivating RASA1 mutations were detected in six families manifesting atypical CMs that were multiple, small, round to oval in shape, and pinkish red in color. In addition to CM, either arteriovenous malformation, arteriovenous fistula, or Parkes Weber syndrome was documented in all the families with a mutation. We named this newly identified association caused by RASA1 mutations "CM-AVM," for capillary malformation-arteriovenous malformation. The phenotypic variability can be explained by the involvement of p120-RasGAP in signaling for various growth factor receptors that control proliferation, migration, and survival of several cell types, including vascular endothelial cells. 相似文献
59.
Whole-genome comparison of leucine-rich repeat extensins in Arabidopsis and rice. A conserved family of cell wall proteins form a vegetative and a reproductive clade 下载免费PDF全文
Baumberger N Doesseger B Guyot R Diet A Parsons RL Clark MA Simmons MP Bedinger P Goff SA Ringli C Keller B 《Plant physiology》2003,131(3):1313-1326
We have searched the Arabidopsis and rice (Oryza sativa) genomes for homologs of LRX1, an Arabidopsis gene encoding a novel type of cell wall protein containing a leucine-rich repeat (LRR) and an extensin domain. Eleven and eight LRX (LRR/EXTENSIN) genes have been identified in these two plant species, respectively. The LRX gene family encodes proteins characterized by a short N-terminal domain, a domain with 10 LRRs, a cysteine-rich motif, and a variable C-terminal extensin-like domain. Phylogenetic analysis performed on the conserved domains indicates the existence of two major clades of LRX proteins that arose before the eudicot/monocot divergence and then diversified independently in each lineage. In Arabidopsis, gene expression studies by northern hybridization and promoter::uidA fusions showed that the two phylogenetic clades represent a specialization into "reproductive" and "vegetative" LRXs. The four Arabidopsis genes of the "reproductive" clade are specifically expressed in pollen, whereas the seven "vegetative" genes are predominantly expressed in various sporophytic tissues. This separation into two expression classes is also supported by previous studies on maize (Zea mays) and tomato (Lycopersicon esculentum) LRX homologs and by information on available rice ESTs. The strong conservation of the amino acids responsible for the putative recognition specificity of the LRR domain throughout the family suggests that the LRX proteins interact with similar ligands. 相似文献
60.