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71.
Although the density and distribution of 5-HT2A(5-hydroxytryptamine-2A) receptors is well established for rat brain, the 5-HT2A receptor distribution and density in guinea pig brain has not been extensively studied. In the present in vitro study, we have utilized 125I-lysergic acid diethylamide ([125I]LSD) to quantify and compare 5-HT2A receptor density in coronal sections of rat and guinea pig brain. Spiperone (1 μM) and sulpiride (1 μM) were used to displace [125I]LSD binding from 5-HT2A and D2 binding sites, respectively. Ligand binding was quantified by computer-aided image analysis densitometry (MCID). Similar to the rat, areas of highest specific 5-HT2A receptor binding (fmol/mg protein) in guinea pig brain included the claustrum and Layer 4 of the cerebral cortex. Significant binding was also found in remaining neocortical layers, islands of Calleja, caudate putamen, olfactory bulb, nucleus accumbens, and choroid plexus. While the rat brain exhibited a high level of specific binding in the tenia tecta and mammillary nuclei, little binding was observed in these regions in the guinea pig. In both rat and guinea pig, low specific binding was found in amygdaloid, thalamic, or cerebellar areas. These studies indicate a general similarity between 5-HT2A binding site distribution and relative density in guinea pig and rat brain but point to a few brain regions where significant differences exist.  相似文献   
72.
I A Taylor  K G Davis  D Watts    G G Kneale 《The EMBO journal》1994,13(23):5772-5778
The type IC DNA methyltransferase M.EcoR124I is a complex multisubunit enzyme that recognizes the non-palindromic DNA sequence GAAN6RTCG. Small angle X-ray scattering has been used to investigate the solution structure of the methyltransferase and of complexes of the enzyme with unmethylated and hemimethylated 30 bp DNA duplexes containing the specific recognition sequence. A major change in the quaternary structure of the enzyme is observed following DNA binding, based on a decrease in the radius of gyration from 56 to 40 A and a reduction in the maximum dimension of the enzyme from 180 to 112 A. The structural transition observed is independent of the methylation state of the DNA. CD shows that there is no change in the secondary structure of the protein subunits when DNA is bound. In contrast, there is a large increase in the CD signal arising from the DNA, suggesting considerable structural distortion which may allow access to the bases targeted for methylation. We propose that DNA binding induces a large rotation of the two HsdM subunits towards the DNA, mediated by hinge bending domains in the specificity subunit HsdS.  相似文献   
73.
74.
The effect of hydration on the conformation and dynamics of the phosphatidylcholine headgroup has been investigated by 2H-NMR measurements of liquid crystalline dioleoylphosphatidylcholine in multilamellar liposomes. Deuterium quadrupole splittings (delta nu Q) and spin-lattice relaxation rates (1/T1) were recorded for three selectively labeled headgroup segments (alpha, beta, and gamma) over the range of water/lipid mole ratios from 4 to 100. The smooth changes in delta nu Q and 1/T1 are found to essentially parallel each other and can be described by a single exponential decay function. Progressive hydration thus induces a concerted change in headgroup conformation together with an increase in its rate of motion (detected by delta nu Q and 1/T1, respectively). The enhanced mobility is partially due to a shift in the lipid phase transition temperature (as monitored by differential scanning calorimetry) and is furthermore attributed to an entropic contribution. It is concluded that the choline dipole becomes slightly raised in its average orientation into the aqueous layer and that the rate is increased at which the headgroup is fluctuating and protruding. The observed molecular changes can thus be accommodated within a model where the effective accessible headgroup volume expands with increasing hydration.  相似文献   
75.
A systematic study of the Vernonia leopoldi complex was undertaken with the objective of determining the taxonomic status of the species involved within this group. TWo species, i.e. Vernonia leopoldi and V. bipontini have been recognized as distinct based on evidence from morphological studies accompanied by field observations and anatomical studies (particularly trichomes and petioles). Both species have 2n = 36 (first reports). Three new varieties have been recognized within V. bipontini , namely var. bipontini , var. gonderensis and var. caccaensis . A lectotype is selected for V. leopoldi .  相似文献   
76.
An Arabidopsis thaliana gene (UBC6) encoding a homologue to ubiquitin-conjugating enzymes has been isolated which is capable of encoding a protein of 183 amino acids of ca. 21 kDa. Northern analysis indicates that the gene is expressed in flowers, seeds and, to a somewhat lesser extent, in 10-day seedlings but not in mature leaves, callus and pre-flowering plants. This pattern of expression is confirmed using transgenic Arabidopsis plants containing a UBC6 promoter-GUS gene fusion construct. These plants displey GUS activity in mature anthers prior to dehiscence, in developing embryos, sepals and the style after pollination.  相似文献   
77.
Abstract: Heterogeneity of the 5-hydroxytryptamine2 (5-HT2) receptor across species has been implicated in several pharmacological and physiological studies. Although 5-HT2 receptors in the rat have been linked to increases in Phosphoinositide (PI) hydrolysis, little evidence exists to support the association of guinea pig 5-HT2 receptors with Pl hydrolysis, the second messenger generally linked with 5-HT2receptors. In the present study, we have taken a molecular and biochemical approach to determining whether species differences in brain 5-HT2 receptors exist between rat and guinea pig. First, we isolated partial cortical 5-HTa receptor cDNA clones that encompassed the third intracellular loop, a receptor area putatively important in receptor-effector coupling. The amino acid sequences deduced from the cDNA clones for rat and guinea pig brain 5-HT2 receptor were 97% homologous. However, the guinea pig 5-HT2 receptor had two tandem substitutions that disrupted a potential alpha helix in the region of the third cytoplasmic loop, which theoretically could alter the intracellular coupling of the guinea pig cortical 5-HT2 receptor. Because of these molecular differences, we examined further the pharmacological activation of the brain 5-HT2 receptor from guinea pig. 5-HT and the 5-HT2 receptor agonist α-methyl-5-HT increased PI hydrolysis in guinea pig cortical slices whereas the 5-HT1c receptor agonist 5-methyltryptamine was significantly less potent. In addition, the 5-HT2 receptor antagonists LY53857, ketanserin, and spiperone blocked 5-HT-stimulated Pl hydrolysis. These pharmacological data suggested that activation of the 5-HT2 receptor in guinea pig cortical slices was associated with PI hydrolysis. Thus, although areas of the guinea pig brain 5-HT2 receptor that influence receptor-effector coupling were different from the rat, such differences were not critical to receptor-effector coupling because, as in the rat, guinea pig brain 5-HT2 receptors were also coupled to PI hydrolysis.  相似文献   
78.
79.
Familial adenomatous polyposis (FAP) is a premalignant disease inherited as an autosomal dominant trait, characterized by hundreds to thousands of polyps in the colorectal tract. Recently, the syndrome has been shown to be caused by mutations in the APC (adenomatous polyposis coli) gene located on chromosome 5q21. We studied two families that both presented a phenotype different than that of the classical form of FAP. The most important findings observed in these two kindreds are (a) low and variable number of colonic polyps (from 5 to 100) and (b) a slower evolution of the disease, with colon cancer occurring at a more advanced age than in FAP in spite of the early onset of intestinal manifestations. To determine whether mutations of the APC gene are also responsible for this variant syndrome, linkage studies were performed by using a series of markers both intragenic and tightly linked to the APC gene. The results provide evidence for exclusion of the APC gene as the cause of the variant form of polyposis present in the two families described.  相似文献   
80.
Cyclins and proto-oncogenes including c-myc have been implicated in eukaryotic cell cycle control. The role of cyclins in steroidal regulation of cell proliferation is unknown, but a role for c-myc has been suggested. This study investigated the relationship between regulation of T-47D breast cancer cell cycle progression, particularly by steroids and their antagonists, and changes in the levels of expression of these genes. Sequential induction of cyclins D1 (early G1 phase), D3, E, A (late G1-early S phase), and B1 (G2 phase) was observed following insulin stimulation of cell cycle progression in serum-free medium. Transient acceleration of G1-phase cells by progestin was also accompanied by rapid induction of cyclin D1, apparent within 2 h. This early induction of cyclin D1 and the ability of delayed administration of antiprogestin to antagonize progestin-induced increases in both cyclin D1 mRNA and the proportion of cells in S phase support a central role for cyclin D1 in mediating the mitogenic response in T-47D cells. Compatible with this hypothesis, antiestrogen treatment reduced the expression of cyclin D1 approximately 8 h before changes in cell cycle phase distribution accompanying growth inhibition. In the absence of progestin, antiprogestin treatment inhibited T-47D cell cycle progression but in contrast did not decrease cyclin D1 expression. Thus, changes in cyclin D1 gene expression are often, but not invariably, associated with changes in the rate of T-47D breast cancer cell cycle progression. However, both antiestrogen and antiprogestin depleted c-myc mRNA by > 80% within 2 h. These data suggest the involvement of both cyclin D1 and c-myc in the steroidal control of breast cancer cell cycle progression.  相似文献   
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