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121.
122.
Jeffery R. Cook Barbara E. Crute Laura M. Patrone Joseph Gabriels Maureen E. Lane Robert G. van Buskirk 《In vitro cellular & developmental biology. Plant》1989,25(10):914-922
Summary We have analyzed the ability of the physical substratum to modulate both the ultrastructural and protein synthetic characteristics
of the Madin-Darby canine kidney (MDCK) renal cell line. When MDCK cells were seeded on Millipore Millicell CM microporous
membrane cell culture inserts they demonstrated a more columnar organization with an increase in cell density sixfold greater
than the same cells seeded on conventional plastic substrata. After 1 wk postseeding on the microporous membrane a partial
basal lamina was noted, with a contiguous basement membrane being apparent after 2 wk. One-dimensional sodium dodecyl sulfate
gel electrophoresis was used to analyze detergent-solubilized proteins from MDCK cells maintained on plastic substrata vs.
microporous membranes. When proteins were pulse-labeled with [35S]methionine, a 55 kDa protein was evident in the cytosolic extract of cells grown on collagen, laminin, and nontreated plastic
substrata; but this labeled protein was not evident in similar extracts from cells grown on collagen and laminin-coated microporous
membranes. To test if the polarized, basement-membrane secreting phenotype of the MDCK cells could be generated on a microporous
membrane without pretreatment with any extracellular matrix (ECM) components, cells were seeded on the Millipore Millicell
HA (cellulosic) microporous membrane. This type of substrata does not need a coating of ECM components for cell attachment.
A partial basement membrane was formed below cells where the basal surface of the cell was planar, but not in areas where
the cell formed large cytoplasmic extensions into the filter. This led us to the conclusion that the microporous nature of
the substrata can dictate both ultrastructural and protein synthetic activities of MDCK cells. Furthermore, we suggest that
both the planar nature of the basal surface and the microporosity of the substrate are corequisites for the deposition of
the basement membrane. 相似文献
123.
The ultrastructure of the mature spermatozoa and spermatogenesis of the bivalve Scrobicularia plana are described. Support cells extend from the basal lamina to the lumen of the testis and are laterally connected to the germinal epithelium. Germ cells present intercellular bridges and flagella since the spermatogonial stage. While spermatogonia and spermatocytes appear connected to support cells by desmosome-like junctions, elongated spermatids are held at the acrosomal region by support cell finger-like processes. During spermiogenesis, the acrosomal vesicle differentiates from a golgian saccule and then migrates to the nuclear apex. A microtubular manchette arising from centrioles surrounds the acrosomal vesicle, the nucleus, and the mitochondria at the time these three organelles start their elongation, disappearing after that. The mature spermatozoon of S. plana lacks a distinct midpiece because the mitochondria extend from the region of the pericentriolar complex along the nucleus anteriorly for approximately 1.4 μm. The features of this bivalve type of modified spermatozoon are compared with those of other animal groups having similar modifications. 相似文献
124.
Bruna Tadolini Diana Fiorentini Laura Landi Luciana Cabrini 《Free radical research》1989,5(4):245-252
To find experimental conditions to selectively study the propagation phase of lipoperoxidation we studied the lipoperoxidation, catalyzed by FeCl2, of liposomes in a buffering condition where Fe2+ autoxidation and oxygen active species generation does not occur. Liposomes from egg yolk phosphatidylcholine. prepared by vortex mixing, do not oxidize Fe2+: on the contrary they oxidize Fe2+ when prepared by ultrasonic irradiation. Dimyristoyl phosphatidylcholine liposomes prepared by ultrasonic irradiation do not oxidize Fe2+. During sonication polyunsaturated fatty acid residues autoxidize and lipid hydroperoxides (LOOH) are generated. Only when LOOH are present in the liposimes Fe2+ oxidizes and its rate of oxidation depends on the amount of LOOH in the assay. The reaction results in the generation of both LOOH and thiobarbituric acid reactive material (TBAR): it is inhibited by butylated hydroxytoluene and has a acidic pH optimum; it is not inhibited by catalase and OH' scavengers. The reaction studied. thus, appears to be the chain branching and propagation phase of lipoperoxidation. When we studied the dependence of Fe2+ oxidation, LOOH and TBAR generation on FeCl2 concentration, we observed that at high FeCl2 concentrations the termination phase of lipoperoxidation was prevalent. Thus. by selecting the appropriate FeCl2 concentration the proposed experimental system allows study of either the propagation or the termination phase of lipoperoxidation. 相似文献
125.
126.
Hormone-induced changes in the in vitro DNA-binding activity of the chicken progesterone receptor 总被引:4,自引:0,他引:4
R Rodriguez M A Carson N L Weigel B W O'Malley W T Schrader 《Molecular endocrinology (Baltimore, Md.)》1989,3(2):356-362
Previous analyses have indicated that steroid hormone receptors undergo an allosteric change in structure upon binding by the steroid ligand. This structural change was envisioned as an intramolecular unmasking of the protein's DNA-binding domain, thus allowing the receptor to function in gene regulation. We report an analysis of the effect of hormone on the DNA-binding activity of the chicken progesterone receptor. Using an isocratic elution of DNA affinity columns we show that unliganded receptor (aporeceptor) can bind a 23-basepair progesterone response element with high affinity and a high degree of sequence preference. Hormone causes a 1.5-fold increase in affinity for the PRE sequence and a 2-fold decrease in affinity for non-specific DNA. Kinetic analysis of the off-rate of receptor-DNA complexes is consistent with this minor effect of hormone. In addition, gel retardation analysis of receptor-progesterone response element complexes further substantiates that hormone is not required for sequence-specific DNA binding. These results indicate that hormone is not necessary for the progesterone receptor to fold into a conformation that recognizes specific gene regulatory sequences. 相似文献
127.
The relation between amino acid sequence and local structure in proteins is investigated. The local structures considered are either the four classes of secondary structure (H, E, T and C) or four classes of local conformations defined using measures of conformational similarity based on distances between C alpha atoms. The classes are obtained by applying an automatic clustering procedure to short polypeptide fragments of uniform length from a database of 75 known protein structures. The thrust of our investigation consists of systematically searching the database for simple amino acid patterns of the type Gly-X-Ala-X-X-Val, where X denotes an arbitrary residue. Patterns that are nearly always associated with the same structure are retained. Finding many such associations, we then evaluate by a statistical approach how many among them are non-random and compare the results for different definitions of local structure. A similar comparison is made for the predictive value of retained associations, which is assessed using an internal test based on dividing the database into "learning" and "test" subsets. While we find that local structures defined by conformational similarity are not superior to secondary structure for prediction purposes, they help us gain insight into the factors that influence the predictive value of derived associations. A major conclusion is that the number of retained associations is in large excess over the number expected from a random correlation between sequence and structure, irrespective of how local conformation is defined. However, only a very small number of these associations can be earmarked as reliable using statistical criteria, due to the limited size of the database. We find, for instance, that the pattern Ala-Ala-X-X-Lys reliably characterizes helix, and the pattern Val-X-Val-X-X-X-Ala reliably characterizes extended structure and beta-strand. The possibility is discussed that these and other reliable associations correspond to regions of the polypeptide chain whose conformations are locally determined and that these regions may play a role in folding. 相似文献
128.
Physella heterostropha size distributions and densities were measured in Pen Branch delta, a thermally altered swamp of the Savannah River, South Carolina. During cessation of thermal input, measurements were taken in a highly impacted area and more natural area. Of the three substrates sampled, logs, small woody material and benthos, snail density was highest on small pieces of submerged wood and < 20% of the snails on logs were out of the water. Following resumption of thermal input, snail density was four times higher on logs than previously measured. Snails responded to elevated water temperatures by congregating in a narrow band slightly above the water. Snail size did not appear to affect their response. However, the thermal history of the snails influenced their behaviour and survival rates. Logs may be a potential refuge for snails when water temperature are greater greater than 38°C. However, our results indicate that long-term survival in this manner may be impossible. 相似文献
129.
Duplication of an Xp segment that includes the ZFX locus causes sex inversion in man 总被引:6,自引:6,他引:0
Gerd Scherer Werner Schempp Carlo Baccichetti Elisabetta Lenzini Franca Dagna Bricarelli Laura Doria Lamba Carbone Ulrich Wolf 《Human genetics》1989,81(3):291-294
Summary Two 46,XY females with tandem duplications of an X short arm segment were studied by cytogenetic and Southern blot analysis. The results show that the duplicated segment in each case included the Xp21.2–Xp22.2 interval, resulting in a double dose of ZFX on the single active X chromosome. The results from our two cases, in conjunction with those reported by other workers, lead us to conclude that the duplication is the reason for the sex inversion. If ZFY and ZFX are indeed sex-determining gene loci, these findings favour a model of sex determination characterized by antagonistic interaction between these genes. 相似文献
130.
P H Rodriguez W J Hamm F Garcia M Garcia V Schirf 《Journal of economic entomology》1989,82(2):519-523
Male and female Aedes aegypti (L.) mosquitoes of the laboratory strain ROCK were irradiated with 130 mw of argon 514.5 nm laser microbeams for 0.04, 0.25, 0.4, and 0.5 s, respectively. Egg production, percentage hatch, and productivity (average number of adults surviving after 3 wk) were used to assess mutagenic effects. Mortality was high for males in all laser radiation groups and increased with time of exposure. Except for the group treated for 0.25 s, significant reductions in total F1 progeny also were demonstrated for all other experimentals when male parents were exposed to laser radiation. Females showed a high mortality when subjected to 0.4- and 0.5-s laser radiation. No F1 progeny were produced when parental females were exposed for 0.25, 0.4, and 0.5 s. Numbers of F1 progeny from females exposed to 0.04 s of laser radiation were significantly reduced. A comparison of weekly mean number of progeny showed that the important differences in productivity occurred during the first and second week, respectively, when either male or female adult parents were subjected to laser radiation. 相似文献