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Lawson L. Winton 《American journal of botany》1968,55(2):159-167
Liquid-grown callus was used to study the nutritional requirements for rooting of a triploid form of normally diploid quaking aspen (Populus tremuloides Michx.). In modified Wolter's liquid medium, tan rough-surfaced spheres of callus grew rapidly when supplied with a high concentration of 2,4-D (0.5 mg/liter), but light-yellow uniformly smooth and firm spheres grew more slowly with a low level of 2,4-D (0.04 mg/liter) plus kinetin. When tissue was grown uncut in liquid for 1, 2, or 3 months, then subcultured to a low-2,4-D agar medium, rooting increased primarily with the age of the source tissue rather than the initial explant size. The surface of the youngest tissue source was almost smooth, but free columnar proliferations extended out from the surface for two or three cells in 2-month-old tissue and for three to six cells in the 3-month-old tissue. The relationship of increased rooting with increased surface cell-proliferation of older tissue was not determined anatomically. 相似文献
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M A Lawson 《The Western journal of medicine》1994,161(4):411-412
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Wayne W. Poon Anthony J. Carlos Brittany L. Aguilar Nicole C. Berchtold Crystal K. Kawano Vahe Zograbyan Tim Yaopruke Michael Shelanski Carl W. Cotman 《The Journal of biological chemistry》2013,288(23):16937-16948
We previously found that BDNF-dependent retrograde trafficking is impaired in AD transgenic mouse neurons. Utilizing a novel microfluidic culture chamber, we demonstrate that Aβ oligomers compromise BDNF-mediated retrograde transport by impairing endosomal vesicle velocities, resulting in impaired downstream signaling driven by BDNF/TrkB, including ERK5 activation, and CREB-dependent gene regulation. Our data suggest that a key mechanism mediating the deficit involves ubiquitin C-terminal hydrolase L1 (UCH-L1), a deubiquitinating enzyme that functions to regulate cellular ubiquitin. Aβ-induced deficits in BDNF trafficking and signaling are mimicked by LDN (an inhibitor of UCH-L1) and can be reversed by increasing cellular UCH-L1 levels, demonstrated here using a transducible TAT-UCH-L1 strategy. Finally, our data reveal that UCH-L1 mRNA levels are decreased in the hippocampi of AD brains. Taken together, our data implicate that UCH-L1 is important for regulating neurotrophin receptor sorting to signaling endosomes and supporting retrograde transport. Further, our results support the idea that in AD, Aβ may down-regulate UCH-L1 in the AD brain, which in turn impairs BDNF/TrkB-mediated retrograde signaling, compromising synaptic plasticity and neuronal survival. 相似文献
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The ATP-dependent interaction of eukaryotic initiation factors with mRNA 总被引:35,自引:0,他引:35
R D Abramson T E Dever T G Lawson B K Ray R E Thach W C Merrick 《The Journal of biological chemistry》1987,262(8):3826-3832
The interaction of three protein synthesis initiation factors, eukaryotic initiation factor (eIF)-4A, -4B, and -4F, with mRNA has been examined. Three assays specifically designed to evaluate this interaction are RNA-dependent ATP hydrolysis, retention of mRNAs on nitrocellulose filters, and cross-linking to periodate-oxidized mRNAs. The ATPase activity of eIF-4A is only activated by RNA which is lacking in secondary structure, and the minimal size of an oligonucleotide capable of effecting an optimal activation is 12-18 bases. In the presence of ATP, eIF-4A is capable of binding mRNA. Consistent with the ATPase activity, this binding shows a definite preference for single-stranded RNA. In the absence of ATP, eIF-4F is the only factor to bind capped mRNAs, and this binding, unlike that of eIF-4A, is sensitive to m7GDP inhibition. The activities of both eIF-4A and eIF-4F are stimulated by eIF-4B, which seems to have no specific independent activity in our assays. Evidence from the cross-linking studies indicates that in the absence of ATP, only the 24,000-dalton polypeptide of eIF-4F binds to the 5' cap region of the mRNA. From the data presented in conjunction with the current literature, a suggested sequence of factor binding to mRNA is: eIF-4F is the first initiation factor to bind mRNA ind an ATP-independent fashion; eIF-4B then binds to eIF-4F, if in fact it was not already bound prior to mRNA binding; and finally, eIF-4A binds to the eIF-4F X eIF-4B X mRNA complex and functions in an ATP-dependent manner to allow unwinding of the mRNA. 相似文献
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The biological significance of peptide hormone glycosylation is uncertain. To examine the effect of Asn-linked glycosylation on calcitonin's bioactivity we purified glycosylated calcitonin from a transplantable rat medullary thyroid carcinoma. Glycosylated calcitonin constituted 2.3% of the total extracted immunoreactive calcitonin. The structure of this peptide differed from nonglycosylated calcitonin only by the oligosaccharide modification of asparagine 3. Affinity of glycosylated calcitonin for lentil lectin indicated that the oligosaccharide was a complex processed form. In a standard in vivo bioassay glycosylated calcitonin had a markedly reduced hypocalcemic activity compared to nonglycosylated calcitonin, an effect most likely due to the presence of the oligosaccharide. 相似文献
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Dissociation of double-stranded polynucleotide helical structures by eukaryotic initiation factors, as revealed by a novel assay 总被引:17,自引:0,他引:17
T G Lawson K A Lee M M Maimone R D Abramson T E Dever W C Merrick R E Thach 《Biochemistry》1989,28(11):4729-4734
A new technique has been applied to the study of the RNA secondary structure unwinding activity of the eukaryotic initiation factors (eIFs) 4F, 4A, and 4B. Secondary structures were generated at the 5' ends of reovirus and globin mRNA molecules by hybridization with 32P-labeled cDNA molecules 15 nucleotide residues long. The dissociation of the labeled cDNAs from the mRNAs was assayed by a gel filtration chromatography procedure which separates the free cDNAs from mRNAs and mRNA/cDNA hybrids. When the three factors were tested alone, only eIF-4F stimulated dissociation of hybrids. The combination of eIF-4A plus eIF-4B also exhibited a strong hybrid dissociating activity, which was markedly temperature dependent. Under optimum conditions, up to 90% of the hybrid structures are disrupted in 60 min. These results demonstrate for the first time that stable double-stranded regions can be melted and dissociated by eIFs. They also characterize more precisely the first step in the structure unwinding reaction. 相似文献