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排序方式: 共有318条查询结果,搜索用时 15 毫秒
71.
Henry Hoppe IV Katherine M. Call Phaik-Mooi Leong William G. Thilly 《Mutation research》1991,250(1-2):411-421
Cell of the human lymphoblast line WI-L2 and its derivative TK-6 were synchronized by centrifugal elutriation and cell-cycle dependent mutation to 6TGR (HPRT) and OUAR (Na+, K+ ATPase) measured. Bromodeoxyuridine induced 6TGR and OUAR mutations within S phase while butylmethylsulfonate induced mutation displayed no cell-cycle dependence. The data indicate that centrifugal elutriation is a facile means to obtain a useful degree of synchrony for these cell lines. 相似文献
72.
Richard W. Joy IV Edward C. Yeung Lisheng Kong Trevor A. Thorpe 《In vitro cellular & developmental biology. Plant》1991,27(1):32-41
Summary The growth and development of white spruce somatic embryos was followed from the filamentous immature to the mature cotyledonary
embryo stage. Histochemical examination of the various stages of embryo development showed that lipids, proteins, and polysaccharides
were produced to varying degrees during the process. During early stages (1 to 2 wk on ABA), mostly polysaccharide was produced,
whereas during later stages, polysaccharides, lipids, and protein accumulated. Electron microscopy indicated that lipid deposition
in somatic embryos started during the first week after transfer to ABA-containing medium. Deposition of the storage products
began at the basal end of the embryonal mass and within the proximal zone of the suspensors. Accumulation continued to the
peripheral regions and then inward toward the cortex of the developing embryo. In all cases, polysaccharide accumulated first,
followed by lipid and lastly, protein. Quantitatively, cotyledonary stage somatic embryos had less lipid and protein and more
starch when compared to zygotic embryos at the same developmental stage. Total protein profiles elucidated by sodium dodecyl
sulfate-polyacrylamide gel electrophoresis indicated that the majority of proteins were similar in zygotic and somatic embryos.
Prominent protein bands were found at 30, 20, 19.5, 15, 14.4, 12, and 10 Kd. However, protein bands at 40, 15, and 12 Kd in
total protein from somatic embryos were either absent or highly underexpressed. 相似文献
73.
Karen E. Sears Jennifer A. Maier Marcelo Rivas-Astroza Rachel Poe Sheng Zhong Kari Kosog Jonathan D. Marcot Richard R. Behringer Chris J. Cretekos John J. Rasweiler IV Zoi Rapti 《PLoS genetics》2015,11(8)
Variation among individuals is a prerequisite of evolution by natural selection. As such, identifying the origins of variation is a fundamental goal of biology. We investigated the link between gene interactions and variation in gene expression among individuals and species using the mammalian limb as a model system. We first built interaction networks for key genes regulating early (outgrowth; E9.5–11) and late (expansion and elongation; E11-13) limb development in mouse. This resulted in an Early (ESN) and Late (LSN) Stage Network. Computational perturbations of these networks suggest that the ESN is more robust. We then quantified levels of the same key genes among mouse individuals and found that they vary less at earlier limb stages and that variation in gene expression is heritable. Finally, we quantified variation in gene expression levels among four mammals with divergent limbs (bat, opossum, mouse and pig) and found that levels vary less among species at earlier limb stages. We also found that variation in gene expression levels among individuals and species are correlated for earlier and later limb development. In conclusion, results are consistent with the robustness of the ESN buffering among-individual variation in gene expression levels early in mammalian limb development, and constraining the evolution of early limb development among mammalian species. 相似文献
74.
Luyao Lu Zijian Yang Kathleen Meacham Abraham Vázquez‐Guardado Mantian Xue Lan Yin Javaneh Boroumand Grace Pakeltis Tian Sang Ki Jun Yu Debashis Chanda Rashid Bashir Robert W. Gereau IV Xing Sheng John A. Rogers 《Liver Transplantation》2018,8(16)
Bioresorbable electronic materials serve as foundations for implantable devices that provide active diagnostic or therapeutic function over a timeframe matched to a biological process, and then disappear within the body to avoid secondary surgical extraction. Approaches to power supply in these physically transient systems are critically important. This paper describes a fully biodegradable, monocrystalline silicon photovoltaic (PV) platform based on microscale cells (microcells) designed to operate at wavelengths with long penetration depths in biological tissues (red and near infrared wavelengths), such that external illumination can provide realistic levels of power. Systematic characterization and theoretical simulations of operation under porcine skin and fat establish a foundational understanding of these systems and their scalability. In vivo studies of a representative platform capable of generating ≈60 µW of electrical power under 4 mm of porcine skin and fat illustrate an ability to operate blue light‐emitting diodes (LEDs) as subdermal implants in rats for 3 d. Here, the PV system fully resorbs after 4 months. Histological analysis reveals that the degradation process introduces no inflammatory responses in the surrounding tissues. The results suggest the potential for using silicon photovoltaic microcells as bioresorbable power supplies for various transient biomedical implants. 相似文献
75.
Many autotrophs vary their allocation to nutrient uptake in response to environmental cues, yet the dynamics of this plasticity
are largely unknown. Plasticity dynamics affect the extent of single versus multiple nutrient limitation and thus have implications
for plant ecology and biogeochemical cycling. Here we use a model of two essential nutrients cycling through autotrophs and
the environment to determine conditions under which different plastic or fixed nutrient uptake strategies are adaptive. Our
model includes environment-independent costs of being plastic, environment-dependent costs proportional to the rate of plastic
change, and costs of being mismatched to the environment, the last of which is experienced by both fixed and plastic types.
In equilibrium environments, environment-independent costs of being plastic select for tortoise strategies—fixed or less plastic
types—provided that they are sufficiently close to co-limitation. At intermediate levels of environmental fluctuation forced
by periodic nutrient inputs, more hare-like plastic strategies prevail because they remain near co-limitation. However, the
fastest is not necessarily the best. The most adaptive strategy is an intermediate level of plasticity that keeps pace with
environmental fluctuations, but is not faster. At high levels of environmental fluctuation, the environment-dependent cost
of changing rapidly to keep pace with the environment becomes prohibitive and tortoise strategies again dominate. The existence
and location of these thresholds depend on plasticity costs and rate, which are largely unknown empirically. These results
suggest that the expectations for single nutrient limitation versus co-limitation and therefore biogeochemical cycling and
autotroph community dynamics depend on environmental heterogeneity and plasticity costs. 相似文献
76.
77.
78.
Grace S. Tan Barry G. Garchow Xuhang Liu Jennifer Yeung John P. Morris IV Trinna L. Cuellar Michael T. McManus Marianthi Kiriakidou 《Nucleic acids research》2009,37(22):7533-7545
Mammalian Argonaute 2 (Ago2) protein associates with microRNAs (miRNAs) or small interfering RNAs (siRNAs) forming RNA-induced silencing complexes (RISCs/miRNPs). In the present work, we characterize the RNA-binding and nucleolytic activity of recombinant mouse Ago2. Our studies show that recombinant mouse Ago2 binds efficiently to miRNAs forming active RISC. Surprisingly, we find that recombinant mouse Ago2 forms active RISC using pre-miRNAs or long unstructured single stranded RNAs as guides. Furthermore, we demonstrate that, in vivo, endogenous human Ago2 binds directly to pre-miRNAs independently of Dicer, and that Ago2:pre-miRNA complexes are found both in the cytoplasm and in the nucleus of human cells. 相似文献
79.
Roman Aranda IV Shauna M. Dineen Rhonda L. Craig James M. Robertson 《Analytical biochemistry》2009,387(1):122-127
Quantification of RNA is essential for various molecular biology studies. In this work, three quantification methods were evaluated: ultraviolet (UV) absorbance, microcapillary electrophoresis (MCE), and fluorescence-based quantification. Viral, bacterial, and eukaryotic RNA were measured in the 500 to 0.05-ng μl−1 range via an ND-1000 spectrophotometer (UV), Agilent RNA 6000 kits (MCE), and Quant-iT RiboGreen assay (fluorescence). The precision and accuracy of each method were assessed and compared with a concentration derived independently using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Cost, operator time and skill, and required sample volumes were also considered in the evaluation. Results indicate an ideal concentration range for each quantification technique to optimize accuracy and precision. The ND-1000 spectrophotometer exhibits high precision and accurately quantifies a 1-μl sample in the 500 to 5-ng μl−1 range. The Quant-iT RiboGreen assay demonstrates high precision in the 1 to 0.05-ng μl−1 range but is limited to lower RNA concentrations and is more costly than the ND-1000 spectrophotometer. The Agilent kits exhibit less precision than the ND-1000 spectrophotometer and Quant-iT RiboGreen assays in the 500 to 0.05-ng μl−1 range. However, the Agilent kits require 1 μl of sample and can determine the integrity of the RNA, a useful feature for verifying whether the isolation process was successful. 相似文献
80.
Saul Lozano-Fuentes Ildefonso Fernandez-Salas Maria de Lourdes Munoz Julian Garcia-Rejon Ken E. Olson Barry J. Beaty William C. Black IV 《PLoS neglected tropical diseases》2009,3(6)