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1.
DNA sequences were determined for three to five alleles of the bride-of-
sevenless (boss) gene in each of four species of Drosophila. The product of
boss is a transmembrane receptor for a ligand coded by the sevenless gene
that triggers differentiation of the R7 photoreceptor cell in the compound
eye. Population parameters affecting the rate and pattern of molecular
evolution of boss were estimated from the multinomial configurations of
nucleotide polymorphisms of synonymous codons. The time of divergence
between D. melanogaster and D. simulans was estimated as approximately 1
Myr, that between D. teissieri and D. yakuba as approximately 0.75 Myr, and
that between the two pairs of sibling species as approximately 2 Myr. (The
boss genes themselves have estimated divergence times approximately 50%
greater than the species divergence times.) The effective size of the
species was estimated as approximately 5 x 10(6), and the average mutation
rate was estimated as 1-2 x 10(-9)/nucleotide/generation. The ratio of
amino acid polymorphisms within species to fixed differences between
species suggests that approximately 25% of all possible single-step amino
acid replacements in the boss gene product may be selectively neutral or
nearly neutral. The data also imply that random genetic drift has been
responsible for virtually all of the observed differences in the portion of
the boss gene analyzed among the four species.
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2.
The contractile basis of amoeboid movement: V. The control of gelation, solation, and contraction in extracts from dictyostelium discoideum 总被引:29,自引:22,他引:7 下载免费PDF全文
Motile extracts have been prepared from Dictyostelium discoideum by homogenization and differential centrifugation at 4 degrees C in a stabilization solution (60). These extracts gelled on warming to 25 degrees Celsius and contracted in response to micromolar Ca++ or a pH in excess of 7.0. Optimal gelation occurred in a solution containing 2.5 mM ethylene glycol-bis (β-aminoethyl ether)N,N,N',N'-tetraacetate (EGTA), 2.5 mM piperazine-N-N'-bis [2-ethane sulfonic acid] (PIPES), 1 mM MgC1(2), 1 mM ATP, and 20 mM KCI at ph 7.0 (relaxation solution), while micromolar levels of Ca++ inhibited gelation. Conditions that solated the gel elicited contraction of extracts containing myosin. This was true regardless of whether chemical (micromolar Ca++, pH >7.0, cytochalasin B, elevated concentrations of KCI, MgC1(2), and sucrose) or physical (pressure, mechanical stress, and cold) means were used to induce solation. Myosin was definitely required for contraction. During Ca++-or pH-elicited contraction: (a) actin, myosin, and a 95,000-dalton polypeptide were concentrated in the contracted extract; (b) the gelation activity was recovered in the material sqeezed out the contracting extract;(c) electron microscopy demonstrated that the number of free, recognizable F-actin filaments increased; (d) the actomyosin MgATPase activity was stimulated by 4- to 10-fold. In the absense of myosin the Dictyostelium extract did not contract, while gelation proceeded normally. During solation of the gel in the absense of myosin: (a) electron microscopy demonstrated that the number of free, recognizable F- actin filaments increased; (b) solation-dependent contraction of the extract and the Ca++-stimulated MgATPase activity were reconstituted by adding puried Dictyostelium myosin. Actin purified from the Dictyostelium extract did not gel (at 2 mg/ml), while low concentrations of actin (0.7-2 mg/ml) that contained several contaminating components underwent rapid Ca++ regulated gelation. These results indicated : (a) gelation in Dictyostelium extracts involves a specific Ca++-sensitive interaction between actin and several other components; (b) myosin is an absolute requirement for contraction of the extract; (c) actin-myosin interactions capable of producing force for movement are prevented in the gel, while solation of the gel by either physical or chemical means results in the release of F-actin capable of interaction with myosin and subsequent contraction. The effectiveness of physical agents in producting contraction suggests that the regulation of contraction by the gel is structural in nature. 相似文献
3.
V KW Wong T Li B YK Law E DL Ma N C Yip F Michelangeli C KM Law M M Zhang K YC Lam P L Chan L Liu 《Cell death & disease》2013,4(7):e720
Autophagy is an important cellular process that controls cells in a normal homeostatic state by recycling nutrients to maintain cellular energy levels for cell survival via the turnover of proteins and damaged organelles. However, persistent activation of autophagy can lead to excessive depletion of cellular organelles and essential proteins, leading to caspase-independent autophagic cell death. As such, inducing cell death through this autophagic mechanism could be an alternative approach to the treatment of cancers. Recently, we have identified a novel autophagic inducer, saikosaponin-d (Ssd), from a medicinal plant that induces autophagy in various types of cancer cells through the formation of autophagosomes as measured by GFP-LC3 puncta formation. By computational virtual docking analysis, biochemical assays and advanced live-cell imaging techniques, Ssd was shown to increase cytosolic calcium level via direct inhibition of sarcoplasmic/endoplasmic reticulum Ca2+ ATPase pump, leading to autophagy induction through the activation of the Ca2+/calmodulin-dependent kinase kinase–AMP-activated protein kinase–mammalian target of rapamycin pathway. In addition, Ssd treatment causes the disruption of calcium homeostasis, which induces endoplasmic reticulum stress as well as the unfolded protein responses pathway. Ssd also proved to be a potent cytotoxic agent in apoptosis-defective or apoptosis-resistant mouse embryonic fibroblast cells, which either lack caspases 3, 7 or 8 or had the Bax-Bak double knockout. These results provide a detailed understanding of the mechanism of action of Ssd, as a novel autophagic inducer, which has the potential of being developed into an anti-cancer agent for targeting apoptosis-resistant cancer cells. 相似文献
4.
High rate of DNA loss in the Drosophila melanogaster and Drosophila virilis species groups 总被引:6,自引:3,他引:3
We recently proposed that patterns of evolution of non-LTR
retrotransposable elements can be used to study patterns of spontaneous
mutation. Transposition of non-LTR retrotransposable elements commonly
results in creation of 5' truncated, "dead-on-arrival" copies. These
inactive copies are effectively pseudogenes and, according to the neutral
theory, their molecular evolution ought to reflect rates and patterns of
spontaneous mutation. Maximum parsimony can be used to separate the
evolution of active lineages of a non-LTR element from the fate of the
"dead-on-arrival" insertions and to directly assess the relative
frequencies of different types of spontaneous mutations. We applied this
approach using a non-LTR element, Helena, in the Drosophila virilis group
and have demonstrated a surprisingly high incidence of large deletions and
the virtual absence of insertions. Based on these results, we suggested
that Drosophila in general may exhibit a high rate of spontaneous large
deletions and have hypothesized that such a high rate of DNA loss may help
to explain the puzzling dearth of bona fide pseudogenes in Drosophila. We
also speculated that variation in the rate of spontaneous deletion may
contribute to the divergence of genome size in different taxa by affecting
the amount of superfluous "junk" DNA such as, for example, pseudogenes or
long introns. In this paper, we extend our analysis to the D. melanogaster
subgroup, which last shared a common ancestor with the D. virilis group
approximately 40 MYA. In a different region of the same transposable
element, Helena, we demonstrate that inactive copies accumulate deletions
in species of the D. melanogaster subgroup at a rate very similar to that
of the D. virilis group. These results strongly suggest that the high rate
of DNA loss is a general feature of Drosophila and not a peculiar property
of a particular stretch of DNA in a particular species group.
相似文献
5.
6.
Paul Maschhoff Sebastian Heene Antonina Lavrentieva Thorleif Hentrop Christian Leibold Marc‐Nils Wahalla Nils Stanislawski Holger Blume Thomas Scheper Cornelia Blume 《Engineering in Life Science》2017,17(5):567-578
Cardiovascular disease is the most common cause of death, accounting for 31% of deaths worldwide. As purely synthetic grafts implicate concomitant anticoagulation and autologous veins are rare, tissue‐engineered vascular grafts are urgently needed. For successful in vitro cultivation of a bioartificial vascular graft, the suitable bioreactor should provide conditions comparable to vasculogenesis in the body. Such a system has been developed and characterized under continuous and pulsatile flow, and a variety of sensors has been integrated into the bioreactor to control parameters such as temperature, pressure up to 500 mbar, glucose up to 4.5 g/L, lactate, oxygen up to 150 mbar, and flow rate. Wireless data transfer (using the ZigBee specification based on the IEEE 802.15.4 standard) and multiple corresponding sensor signal processing platforms have been implemented as well. Ultrasound is used for touchless monitoring of the growing vascular structure as a quality control before implantation (maximally achieved ultrasound resolution 65 μm at 15 MHz). To withstand the harsh conditions of steam sterilization (120°C for 20 min), all electronics were encapsulated. With such a comprehensive physiologically conditioning, sensing, and imaging bioreactor system, all the requirements for a successful cultivation of vascular grafts are available now. 相似文献
7.
8.
Typical preparation of seed samples for infrared (IR) microspectroscopy involves imbibition of the seed for varying time periods followed by cryosectioning. Imbibition, however, may initiate germination even at 4° C with associated changes in the chemistry of the sample. We have found that it is possible to section seeds that are sufficiently hard, such as soybeans, on a standard laboratory microtome without imbibition. The use of dry sectioning of unimbibed seeds is reported here, as well as a comparison of different mounting media and modes of analysis. Glycerol, Tissue-Tek, and ethanol were used as mounting media, and the quality of the resulting spectra was assessed. Ethanol was the preferred mountant, because it dried quickly with no residue and thus did not interfere with the spectrum of interest. Analysis in transmission mode using barium fluoride windows to hold the samples was compared with transmission-reflection analysis with sections mounted on special infrared-reflecting slides. The two modes of analysis performed well in different regions of the spectrum. The mode of analysis (transmission vs. transmission-reflection) should be based on the components of greatest interest in the sample. 相似文献
9.
The binding of LMWH-tyr-FITC to granulocytes, monocytes, and lymphocytes was analyzed by flow cytometry using a low-molecular-weight heparin (LMWH) labeled with fluorescein-5-isothiocyanate (FITC). FITC was covalently bound to tyramine, which was synthesized to LMWH by endpoint-attachment (Malsch et al.: Anal Biochem 217:255-264, 1994). The binding was rapid, specific, dose-dependent, saturable, and reversible. To investigate the molecular weight dependence of heparins, heparin-derived di- to dodecasaccharides were used. With decreasing molecular weight, the amount of oligosaccharides increased; these were bound to granulocytes, monocytes, and lymphocytes (r = -0.77). The degree of sulfation of non-heparin glycosaminoglycans influenced the binding to leukocytes. Decreasing the degree of sulfation decreased the binding. The pentasaccharide did not bind as strongly as the other heparin-derived oligosaccharides, indicating an AT III-independent mechanism. Two classes of heparin binding sites were identified on granulocytes and one class of binding sites on monocytes and lymphocytes. The lowest amount of LMWH-tyr-FITC detected was 1 ng on granulocytes, 0.18 ng on monocytes and 0.01 ng on lymphocytes. The data suggest that heparin and other sulfated polysaccharides may play a role in the physiology of thrombosis, arteriosclerosis, and inflammation by binding to granulocytes, monocytes, and lymphocytes. 相似文献
10.