Variations in regulatory regions of developmental control genes have been implicated in the divergence of axial morphologies. To find potentially significant changes in cis-regulatory regions, we compared nucleotide sequences and activities of mammalian Hoxc8 early enhancers. The nucleotide sequence of the early enhancer region is extremely conserved among mammalian clades, with five previously described cis-acting elements, A-E, being invariant. However, a 4-bp deletion within element C of the Hoxc8 early enhancer sequence is observed in baleen whales. When assayed in transgenic mouse embryos, a baleen whale enhancer (unlike other mammalian enhancers) directs expression of the reporter gene to more posterior regions of the neural tube but fails to direct expression to posterior mesoderm. We suggest that regulation of Hoxc8 in baleen whales differs from other mammalian species and may be associated with variation in axial morphology. 相似文献
Alkylation of aromatics catalyzed by solid acids constitutes a class of reactions of both academic and industrial importance.
Among alkylation reactions, isopropylation of aromatic compounds has attracted considerable attention. Use of propylene as
alkylating agent at very high temperatures leads to coke formation which results in deactivation of the catalyst. The use
of isopropanol (IPA) as an alkylating agent is attractive when propylene is not readily available. In situ dehydration of
IPA leads to prolonged activity since water of reaction suppresses coke formation. Further, IPA dehydration also generates
diisopropyl ether which itself is an excellent alkylating agent. Alkylation of mesitylene with propylene or IPA results in
the formation of 2-isopropyl-mesitylene (2-IPMT), which is almost extensively used as a precursor in a number of industrial
chemicals. This work covers the evaluation of clay-supported heteropolyacids and sulfated zirconia. A variety of solid acid
catalysts such as K-10 clay, sulfated zirconia, Filtrol-24, 20% w/w dodecatungstophosphoric acid (H3PW12O40, DTP) supported on K-10 montmorillonite clay and 20% w/w cesium substituted dodecatungstophosphoric acid (Cs2.5H0.5PW12O40, Cs-DTP) supported on K-10 montmorillonite clay were investigated for the liquid phase isopropylation of mesitylene to 2-IPMT
using IPA at much milder conditions vis-à-vis other catalysts reported so far. 20% w/w Cs-DTP/K-10 clay was found to be the
best catalyst which gives 98% conversion of limiting component, IPA and 98% selectivity towards the desired product, 2-IPMT
after 2 h of total reaction time. This catalyst could be reused without any further chemical treatment, eliminating the effluent
disposal problems. The reaction was carried out without using any solvent and the process subscribes to the principles of
green chemistry. The catalytic activity is in the following order: 20% w/w Cs-DTP/K-10 clay (most active) > 20% w/w DTP/K-10
clay > Filtrol-24 > Sulfated zirconia > K-10 clay (least active). The effect of various operating parameters and catalyst
reusability were also systematically investigated. A mathematical model was proposed to probe into the intricate reaction
kinetics and mechanism consistent with the experimental results. The reaction is free from any external mass transfer as well
as intraparticle diffusion limitations and is intrinsically kinetically controlled. An overall second order kinetic equation
was used to fit the experimental data, under the assumption that all the species are weakly adsorbed on the catalytic sites. 相似文献
A highly practical, one‐step, facile synthesis of aromatic, heteroaromatic, allylic and aliphatic nitriles from primary alcohols catalyzed by ferric nitrate [Fe(NO3)3⋅9H2O] in the presence of TEMPO, aqueous ammonia and air at room temperature is described.
Ag/ZnO nano-hetero-junctions were synthesized by an electrochemical route. The optical absorption spectroscopy and photoluminescence studies reveal the reaction mechanism at the junction. Optical absorption spectra indicate presence of well-defined ZnO excitonic feature along with the Ag surface plasmon absorption feature at 400 nm. Moreover, ZnO green photoluminescence appears on junction formation with Ag. Detailed analysis of emission and excitation processes indicate that efficient charge transfer is taking place from ZnO to Ag. Ag is also responsible for creation of levels in the HOMO-LUMO gap of ZnO. This finding may be of relevance so far as p-type doping in ZnO is concerned. 相似文献
We have used a transgene mutation approach to study how expression domains of Hoxc8 are established during mouse embryogenesis. A cis-regulatory region located 3 kb upstream from the Hoxc8 translational start site directs the early phase of expression. Four elements, termed A, B, C, and D, were previously shown to direct expression to the neural tube. Here we report that a fifth element, E, located immediately downstream of D directs expression to mesoderm in combination with the other four elements. These elements are interdependent and partially redundant. Different combinations of elements determine expression in different posterior regions of the embryo. Neural tube expression is determined minimally by ABC, ABD, or ACD; somite expression by ACDE; and lateral plate mesoderm expression by DE. Neural tube and lateral plate mesoderm enhancers can be separated, but independent somite expression has not been achieved. Furthermore, mutations within these elements result in posteriorization of the reporter gene expression. Thus, the anterior extent of expression is determined by the combined action of these elements. We propose that the early phase of Hoxc8 expression is directed by two separate mechanisms: one that determines tissue specificity and another that determines anterior extent of expression. 相似文献
Hox genes are expressed in dynamic patterns during embryogenesis consistent with their role in axial specifications. To study the distribution of mouse Hoxc8, a homeodomain containing protein, we raised monoclonal antibodies against the least conserved portion of Hoxc8. Using these antibodies, we have examined early and mid-gestation embryos for the distribution of the protein. At the end of gastrulation Hoxc8 is expressed in the caudal portion of the embryo. In the neural tube, an early phase when all cells express Hoxc8 is distinguished from a late phase with predominant expression in differentiating neurons. A comparison of this expression pattern with that of a reporter gene under the control of the early Hoxc8 enhancer demarcates three separate regulatory components: (1) initiation and establishment; (2) maintenance; and (3) downregulation. We propose that Hoxc8 expression during embryogenesis is established in multiple phases. Possible regulatory mechanisms involved in generating such a complex domain of Hox gene expression are discussed. 相似文献
When administered before training to 23-day-old Long-Evans rats, scopolamine hydrobromide significantly impaired both contextual and auditory-cue fear conditioning in a dose-dependent manner. Methylscopolamine which does not cross the blood-brain barrier, however, had no effect on either form of conditioned fear. Scopolamine administered up to 3 h after training also impaired both forms of fear conditioning when administered following a single pairing of the auditory cue and shock. When rats received three pairings, however, a posttraining treatment with scopolamine only impaired contextual fear conditioning. These results suggest that central cholinergic systems are involved in the posttrial processes that establish the memory trace for the conditioning experience. 相似文献
Conducting polyaniline powder was synthesized chemically and paints containing conducting polyaniline powder were applied on low carbon steel samples. The conducting polyaniline powder was characterized by UV-Visible absorption spectroscopy and the morphology of paint coating on low carbon steel was studied by scanning electron microscopy. The corrosion protection performance of the coating was evaluated by using potentiodynamic polarization techniques and electrochemical impedance spectroscopy. It has been found that the 2 wt % polyaniline-hydrochloric acid based paint coating offers maximum corrosion protection to low carbon steel in chloride medium. 相似文献