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1.
We propose a mathematical model for pendelluft flow in a single airway bifurcation. The model is motivated by an apparatus used in an experimental study of the pendelluft by Ultman et al. (1988). We derive differential equations governing the fluid flow, which directly connect physiological parameters to the variables determining the pendelluft; this approach allows us to include nonlinearity in the model. If nonlinearity is neglected, our model is identical to the R-I-C circuits used by previous investigators. If nonlinearity is retained, we show that pendelluft can occur even in perfectly symmetric airway bifurcations. For the specific apparatus used in the experiments of High et al. (1991), we demonstrate that two qualitatively different pendelluft flows can occur in the system. 相似文献
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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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Soluble complexes were formed between C1q, a subunit of the first component of human complement, and four different Waldenstr?m IgM proteins at reduced ionic strengths. The equilibria between these complexes and the free proteins were studied in the ultracentrifuge. Complex formation was found to be a very sensitive function of the salt concentration, and at physiological ionic strength complex formation was negligible. The complexes were cross-linked with a water-soluble carbodiimide and separated by sucrose gradient centrifugation. Both 22 S 1:1 and 26 S 2:1 C1q X IgM complexes were formed; stoichiometry was established by cross-linking 125I-C1q with 131I-IgM and determining the ratios of the specific activities of the gradient-purified materials. The association process was studied as a function of protein concentration and was analyzed by Scatchard and Hill plots to yield stoichiometry, association constant, and degree of cooperativity. The results indicated that IgM has two identical and independent binding sites for C1q. The intrinsic association constant was found to vary between 10(6) M-1 at 0.084 M ionic strength to 10(4) M-1 at physiological ionic strength; the slope of the log-log plot gave a value of -6.0. The cross-linked complexes were examined by electron microscopy, and the C1q appeared to be attached to the IgM through the C1q heads, implying that the biologically significant binding sites were involved in this interaction. For the 2:1 complexes, the two C1q appeared to attach to opposite surfaces of the IgM, suggesting the presence of a pseudo-2-fold axis lying in the plane of the IgM disk. 相似文献
6.
Relative molecular mass determination of a major, highest relative molecular mass extracellular amelogenin of developing bovine enamel 总被引:1,自引:0,他引:1
Proteins of developing bovine enamel were fractionated by molecular sieving and ion-exchange chromatography. The major fraction corresponding to the highest Mr amelogenin of Mr approximately 26 000-30 000 was isolated and its Mr determined by SDS-PAGE, molecular sieving on G-100 resin and high performance liquid chromatography and by sedimentation-equilibrium ultracentrifugation, the latter three procedures in guanidine hydrochloride. SDS-PAGE and HPLC molecular sieving, employing commonly used Mr standards, gave Mr values of approximately 22 000-26 000. SDS-PAGE and HPLC molecular sieving, using proline-rich CNBr peptides of collagen as standards, and sedimentation-equilibrium ultracentrifugation, gave Mr values of approximately 15 000-18 000 and approximately 17 385, respectively. These latter values correspond well with those reported earlier and with the Mr of the major amelogenin computed from recent amino acid sequence data (approximately 19 000). It is concluded that the recently described, highest Mr amelogenin of Mr = 26 000-30 000 is not a new component but is identical to the proline-rich components having relative molecular masses ranging from 15 000 to 18 000 described much earlier by several groups of workers. 相似文献
7.
Summary Complex carbohydrates in the human cervix were studied histochemically using lectins, conjugated to horseradish peroxidase and correlated procedures. Stratified squamous epithelium of the exocervix and columnar epithelium of the endocervix in some, but not all specimens showed staining for terminal -N-acetyl-d-galactosamine, -d-galactose, -d-galactose and -l-fucose. the staining for -N-acetylgalactosamine and -galactose, the terminal sugars in blood group A and B antigens respectively, corresponded to a large extent with ABO blood type. One exception was the lack of staining for terminal -N-acetylgalactosamine in endocervical secretions in three of nine blood type A patients. A second exception was the staining for terminal -galactose in endocervical secretions in about half of blood type O and A specimens. The type and amount of glycoprotein formed by endocervical columnar cells differed according to location in superficial compared with deep portions of the glands and according to location at the junction with exocervix compared with the more internal regions. Staining of endothelial cells for blood group A and B antigens was confined to subjects of blood type A and B respectively, although three of nine type A specimens showed no lectin reactivity for group, A antigen. Endothelial cells evidenced affinity forUlex europeus I agglutinin demonstrative of fucose in all specimens. Mast cells disclosed lectin affinity consistent with the presence of terminal or internal mannose orN-acetylglucosamine residues. Two blood type O specimens were examined with conjugated lectins at the ultrastructural level. Secretory granules stained for content of terminal -galactose, -galactose and fucose. These results support and concur with biochemical studies of complex carbohydrates in human cervical tissues. They reveal, in addition, the location of the blood group antigens in the human exocervix and endocervix and the marked heterogeneity among endocervical columnar cells in glycoprotein production. 相似文献
8.
Codon usage in the vertebrate hemoglobins and its implications 总被引:2,自引:0,他引:2
A study of codon usage in vertebrate hemoglobins revealed an evolutionary
trend toward elevated numbers of CpG codon boundary pairs in mammalian
hemoglobin alpha genes. Selection for CpG codon boundaries countering the
generally observed CpG suppression is strongly suggested by these data.
These observations parallel recently published experimental results that
indicate that constitutive expression of the human alpha-globin gene
appears to be determined by regulatory information encoded within the
structural gene. The possibility is raised that, in the absence of
selection, CpG decay can be used to date the evolutionary origin of a
mammalian alpha pseudogene from its active alpha gene.
相似文献
9.
Evolution of crystallins: expression of lens-specific proteins in the blind mammals mole (Talpa europaea) and mole rat (Spalax ehrenbergi) 总被引:3,自引:0,他引:3
Quax-Jeuken Y; Bruisten S; Bloemendal H; de Jong WW; Nevo E 《Molecular biology and evolution》1985,2(4):279-288
The mole (Talpa europaea; Insectivora) and the mole rat (Spalax ehrenbergi;
Rodentia) both have degenerated eyes as a convergent adaptation to
subterranean life. The rudimentary eye lenses of these blind mammals no
longer function in a visual process. The crystallin genes, which display a
lens-specific expression pattern, were studied in these blind mammals and
in related species with normal eyes by hybridizing their genomic DNAs with
probes obtained from cDNA clones for alpha A-, alpha B-, and beta
Bp-crystallins from calf and gamma 3- crystallin from the rat. For all
crystallin genes examined, the hybridization signals of mole and mole rat
genomic DNA were comparable, respectively, with those of shrew and of rat
and mouse, normal-vision representatives of the orders Insectivora and
Rodentia. The expression of the crystallins at the protein level was tested
by using antiserum specific for alpha-crystallin in immunofluorescence
reactions on lens sections of mole and mole rat eyes and by using antisera
against the beta- and gamma-crystallins on sections of the mole eye. All
antisera gave positive fluorescence reactions exclusively with lens tissue
of these blind mammals, indicating that the crystallins are still normally
expressed despite the fact that these lenses have had no function in a
visual process in these mammals for at least many million years. These
findings apparently imply that some unknown selective advantage has
conserved the crystallin genes and their expression after the loss of
normal function of the lenses.
相似文献
10.
A random, unique DNA sequence has been isolated and assigned to human chromosome 8. This sequence (D8MGV1) recognizes two alleles that differ in size by 700 bp. 相似文献