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  • 1
    Electronic Resource
    Electronic Resource
    Embryonic transcriptional activation of aXenopus cytoskeletal actin gene does not require a serum response element (1990)
    Springer
    Development genes and evolution 199 (1990), S. 89-96 
    Details
    ISSN: 1432-041X
    Keywords: Amphibian embryo ; Transcriptional regulation ; Serum response element ; Microinjection ; In vitro mutagenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The Serum Response Element (SRE) is a sequence motif which activates transcription of certain genes in response to factors that stimulate cell proliferation. This motif is found in the promoter of aXenopus laevis cytoskeletal actin gene, which is transcriptionally activated very early in embryonic development. We tested whether the SRE plays a role in the developmentally-timed transcriptional activation of this gene by constructing an SRE replacement mutant and studying its transcription after microinjection intoXenopus embryos. Normal amounts of actin mRNA are transcribed at the normal time in development from this mutant, suggesting that the SRE is not the sole determinant of temporal specificity of actin gene transcription in the embryo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02029555
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  • 2
    Electronic Resource
    Electronic Resource
    Measurements of carbon thin films using x-ray reflectivity (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 1861-1863 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report x-ray reflectivity measurements on ultrathin (∼250 A(ring)) amorphous carbon films and show that for film thicknesses of a few hundred angstroms this is an extremely effective, accurate, and nondestructive technique for measuring the thickness, density, and microscopic surface roughness. These properties are difficult to accurately measure using other methods. However, since they affect the functional performance of these films and are dependent on preparation conditions, their determination is particularly important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344361
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  • 3
    Electronic Resource
    Electronic Resource
    A data collection program for x-ray diffractometry : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 992-994 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A computer program for controlling diffractometers is described. At present it is capable of controlling a four-circle diffractometer in a variety of calculation modes, a two-circle diffractometer, and also a z-axis diffractometer. The program includes on-screen plotting of both the current scan and previous scans. There is a separate program which consists of the plotting subset of the commands so that while one user is collecting data other users can be analyzing old data simultaneously. Extensive on-line help is provided. The program is written in fortran, runs on the VMS operating system, and is primarily dependent on CAMAC for data collection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143718
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  • 4
    Electronic Resource
    Electronic Resource
    Structural depth profiling of iron oxide thin films using grazing incidence asymmetric Bragg x-ray diffraction (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 4763-4768 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray depth profiling in a grazing incidence asymmetric Bragg geometry is used to obtain the depth-dependent structure of a nominally γ-Fe2O3 thin film, which was oxidized from an Fe3O4 film. As the incidence angle is varied from angles less than the critical angle for total external reflection to angles greater than the critical angle, the x-ray penetration depth increases from about 20 to several thousand angstroms. The observed diffraction originates from this region of variable depth and a structural depth profile of the thin film can be obtained by measuring the diffraction pattern as a function of incidence angle. The iron oxide film is found to have a 45-A(ring)-thick surface layer of α-Fe2O3; beneath this layer the film is predominantly γ-Fe2O3 but also contains about 2.6 at. % α-Fe2O3. These data, together with previous chemical and magnetic data, suggest that during oxidation of the Fe3O4 film the surface layer forms by the outward diffusion of Fe ions and their subsequent oxidization to α-Fe2O3. One possible explanation of the 2.6% α-Fe2O3 in the bulk of the film is that the Fe3O4 film contains small nuclei of material that are structurally similar to α-Fe2O3. During the oxidation to form γ-Fe2O3, these then grow to form small grains of α-Fe2O3 that are observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343230
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  • 5
    Electronic Resource
    Electronic Resource
    Renin inhibitors containing esters at the P2-position. Oral activity in a derivative of methyl aminomalonate (1991)
    s.l. : American Chemical Society
    Journal of medicinal chemistry 34 (1991), S. 1935-1943 
    Details
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/jm00111a002
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  • 6
    Electronic Resource
    Electronic Resource
    A Wide-Bandpass Multilayer Monochromator for Biological Small-Angle Scattering and Fiber Diffraction Studies (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 672-682 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Many biological applications of small-angle X-ray scattering, in particular time-resolved studies, are often limited by the flux incident on the sample due to the smaller scattering cross section of biological specimens. The wider-energy bandpass of a monochromator that consists of a pair of synthetic multilayer microstructures can, in principle, provide a flux two orders of magnitude higher than that of an Si(111) double-crystal monochromator. Two types of multilayers have been installed in the standard monochromator tank of beamline 4-2 at the Stanford Synchrotron Radiation Laboratory; the multilayer beam has been characterized for studies of small-angle X-ray scattering/diffraction from biological materials. Reflectivity and topography measurements indicate that the multilayers are quite adequate for these applications and a pair of Mo/B4C multilayers provided a 10–30 times increase in flux, compared with the flux level obtained with an Si(111) double-crystal monochromator. The increased flux level is very useful in time-resolved scattering studies as well as for recording weak scattering at higher angles. Having carried out many solution scattering and fiber diffraction experiments, we conclude that the use of multilayer does not result in significant broadening of diffraction peaks nor does it have appreciable effects on small-angle resolution. No significant increase in background is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889898002702
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  • 7
    Electronic Resource
    Electronic Resource
    Uptake and release of63Ni2+ byXenopus embryos during early cleavage stages (1990)
    Springer
    BioMetals 2 (1990), S. 214-218 
    Details
    ISSN: 1572-8773
    Keywords: Nickel metabolism ; Nickel toxicology ; Xenopus laevis ; Embryogenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Uptake and release of63Ni was studied in dejelliedXenopus laevis embryos exposed to63Ni2+ (0.3–30 μmol/1) for 0.5-h intervals during the period 1–4.5 h post-fertilization (i.e. from first cleavage to early blastula stage). At first cleavage, the mean uptake of63Ni by embryos was 12-17 times that by non-fertilized eggs, suggesting that conversion of the vitelline envelope to the fertilization envelope enhanced integumental permeability to63Ni2+. 63 Ni uptake by embryos at the 1-2-cell stage averaged 1.8–2.5 times that at the early blastula stage. An average of 5% of total63Ni in washed embryos was recovered in isolated fertilization envelopes, indicating that63Ni2+ passed through the envelope into internal compartments. Progressive increases of63Ni uptake were seen with increasing exposure levels; after exposure during 1–1.5 h post-fertilization to the highest concentration of63Ni2+ (30 μmol/1),63Ni uptake averaged 11.4 (SD±5.1) pmol/embryo. Rapid efflux of63Ni was noted after63Ni2+-exposed embryos were transferred to nickel-free medium; mean63Ni contents at 0.25 h and 2 h post-exposure diminished to 50% and 15% of the initial values, regardless of the exposure level. The finding thatXenopus embryos are permeable to63Ni2+ during early cleavage stages provides a convenient experimental system to investigate the embryotoxicity and teratogenicity of nickel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01141362
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  • 8
    Electronic Resource
    Electronic Resource
    Molecular approaches to the study of mesoderm formation in amphibians (1987)
    New York, NY : Wiley-Blackwell
    BioEssays 6 (1987), S. 52-57 
    Details
    ISSN: 0265-9247
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The mesoderm is the region of the embryo that gives rise to muscle, blood and connective tissues; it becomes segregated from the ectoderm and endoderm at gastrulation. Embryological studies have revealed, however, that the potential for certain embryonic cells to become part of the mesoderm is established well before gastrulation, most likely through an extracellular signalling process termed ‘induction’. The recent characterization of mesoderm-specific mRNAs and proteins now permits an analysis of the very earliest events involved in the specification of the mesoderm at the molecular level. Such experiments should contribute to our understanding of the mechanisms involved in controlling cell differentiation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bies.950060203
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  • 9
    Electronic Resource
    Electronic Resource
    Sequence requirements for embryonic transcriptional activation of a gastrula-specific actin gene in Xenopus laevis (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 30 (1991), S. 293-303 
    Details
    ISSN: 1040-452X
    Keywords: Cytoskeletal actin gene ; Microinjection ; Promoter mapping ; Transcriptional regulation ; Xenopus embryo ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: Cytoskeletal actin genes undergo developmentally timed transcriptional activation at the gastrula stage of embryonic development in the amphibain Xenopus laevis. To study the regulation of this process, a molecularly marked cloned actin gene has been introduced into living embryos by microinjection, and levels of its transcripts (which are distinct from endogenous actin message) have been measured by RNase protection. In vitro mutagenesis of the marked gene, followed by microinjection and transcriptional analysis of various mutants, has been used to search for gene sequences that participate in accurate transcriptional initiation and developmental control. Deletion mutants containing only 90 nucleotides of upstream sequence undergo correct developmental regulation, while deletion to -33 prevents normal activation of the gene. In the presence of sufficient upstream sequence, an actin-globin fusion gene, containing only 564 nucleotides downstream of the actin gene transcription startsite, is correctly activated. Taken together, these results imply that all sequences necessary for correct temporal regulation reside between -90 and +564 nucleotides, with respect to the transcriptional start site of the actin gene. They further suggest that developmental activation of actin gene transcription may involve either (1) interaction of non-DNA binding proteins with basal transcription factors, or (2) the concerted action of ubiquitous promoter-binding factors and factors that interact with downstream regulatory regions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080300403
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  • 10
    Electronic Resource
    Electronic Resource
    Developmental regulation of a serum response element binding activity in amphibian embryos (1991)
    New York, NY [u.a.] : Wiley-Blackwell
    Molecular Reproduction and Development 29 (1991), S. 323-336 
    Details
    ISSN: 1040-452X
    Keywords: DNA-binding proteins ; Serum response element ; GC box ; Transcriptional regulation ; Cytoskeletal actin gene ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: As part of our studies of transcriptional control during early development in vertebrates, we have examined embryos of the amphibian Xenopus laevis for the presence of sequence-specific DNA-binding proteins, using gel electrophoresis mobility-shift assays. Our analysis has focused on sequence elements in the cytoskeletal actin gene, whose embryonic transcription is initially activated at the gastrula stage, approximately 16 hours after fertilization. We detect activites capable of specific binding to two known transcriptional regulatory elements, the serum response element and the GC-box, located in the 5′-flanking region of the cytoskeletal actin gene. Binding activity specific for a region downstream of the transcriptional startsite is also detected, in a region which may be involved in controlling developmental activation of this gene. Serum response element-binding activity, as well as the downstream binding activity, is enriched in extracts from gastrula and neurula stage embryos, compared to egg extracts, suggesting that increased levels of one or both of these activities might play a role in developmentally timed transcriptional activation of the cytoskeletal actin gene in the embryo.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrd.1080290403
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