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71.
We have used hydrothermal isometric tension (HIT) techniques in a sheep model to assess collagen crosslink stability and its contribution to the mechanical properties of the ovine thoracic aorta during perinatal and postnatal development. Aortic tissue was studied from fetal sheep, lambs, and adult sheep. Strips of tissue were loaded under isometric tension and heated to a 90 degrees C isotherm which was sustained for 3 hours. The decrease in load at this temperature is associated with collagen peptide bond hydrolysis and chain slippage, and the rate of this decrease is an inverse indicator of collagen crosslinking. The half-time of load decay (t1/2) was computed before and after tissue was treated with NaBH4 which stabilizes immature, reducible crosslinks. We observed a two-fold increase in t1/2 of untreated tissue from the lamb to the adult, indicating that aortic collagen crosslinking increased during postnatal development. Furthermore, the t1/2 of NaBH4-stabilized lamb tissue was similar to that of the untreated adult tissue, suggesting that much of the immature crosslinking in the lamb is stabilized during postnatal development. These observations suggest (a) increased crosslinking occurs during postnatal development and (b) that this increase is largely due to a conversion of immature crosslinks into their mature heat stable form. 相似文献
72.
Wolfgang H. Goldmann Reinhard Galneder Markus Ludwig Weiming Xu Eileen D. Adamson Ning Wang Robert M. Ezzell 《Experimental cell research》1998,239(2):235
We have investigated a mouse F9 embryonic carcinoma cell line, in which both vinculin genes were inactivated by homologous recombination, that exhibits defective adhesion and spreading [Collet al.(1995)Proc. Natl. Acad. Sci. USA92, 9161–9165]. Using a magnetometer and RGD-coated magnetic microbeads, we measured the local effect of loss and replacement of vinculin on mechanical force transfer across integrins. Vinculin-deficient F9Vin(−/−) cells showed a 21% difference in relative stiffness compared to wild-type cells. This was restored to near wild-type levels after transfection and constitutive expression of increasing amounts of vinculin into F9Vin(−/−) cells. In contrast, the transfection of vinculin constructs deficient in amino acids 1–288 (containing the talin- and α-actinin-binding site) or substituting tyrosine for phenylalanine (phosphorylation site, amino acid 822) in F9Vin(−/−) cells resulted in partial restoration of stiffness. Using atomic force microscopy to map the relative elasticity of entire F9 cells by 128 × 128 (n= 16,384) force scans, we observed a correlation with magnetometer measurements. These findings suggest that vinculin may promote cell adhesion and spreading by stabilizing focal adhesions and transferring mechanical stresses that drive cytoskeletal remodeling, thereby affecting the elastic properties of the cell. 相似文献
73.
Out of Africa and back again: nested cladistic analysis of human Y chromosome variation 总被引:18,自引:3,他引:15
Hammer MF; Karafet T; Rasanayagam A; Wood ET; Altheide TK; Jenkins T; Griffiths RC; Templeton AR; Zegura SL 《Molecular biology and evolution》1998,15(4):427-441
We surveyed nine diallelic polymorphic sites on the Y chromosomes of 1,544
individuals from Africa, Asia, Europe, Oceania, and the New World.
Phylogenetic analyses of these nine sites resulted in a tree for 10
distinct Y haplotypes with a coalescence time of approximately 150,000
years. The 10 haplotypes were unevenly distributed among human populations:
5 were restricted to a particular continent, 2 were shared between Africa
and Europe, 1 was present only in the Old World, and 2 were found in all
geographic regions surveyed. The ancestral haplotype was limited to African
populations. Random permutation procedures revealed statistically
significant patterns of geographical structuring of this paternal genetic
variation. The results of a nested cladistic analysis indicated that these
geographical associations arose through a combination of processes,
including restricted, recurrent gene flow (isolation by distance) and range
expansions. We inferred that one of the oldest events in the nested
cladistic analysis was a range expansion out of Africa which resulted in
the complete replacement of Y chromosomes throughout the Old World, a
finding consistent with many versions of the Out of Africa Replacement
Model. A second and more recent range expansion brought Asian Y chromosomes
back to Africa without replacing the indigenous African male gene pool.
Thus, the previously observed high levels of Y chromosomal genetic
diversity in Africa may be due in part to bidirectional population
movements. Finally, a comparison of our results with those from nested
cladistic analyses of human mtDNA and beta-globin data revealed different
patterns of inferences for males and females concerning the relative roles
of population history (range expansions) and population structure
(recurrent gene flow), thereby adding a new sex-specific component to
models of human evolution.
相似文献
74.
75.
L. Desprs F. J. Kruger D. Imbert-Establet M. L. Adamson 《International journal for parasitology》1995,25(12):1509-1514
The internal transcribed spacer region of the ribosomal RNA, ITS2, was sequenced from a singlé specimen of S. hippopotami collected from a pulmonary artery of the hippopotamus, Hippopotamus amphibius in South Africa. The nucleotide sequence was aligned with those of S. mansoni, S. rodhaini, S. haematobium, S. intercalatum, S. curassoni. S bovis and S. japonicum. Both maximum parsimony and genetic distance analyses were performed on these data sets. Using S. japonicum as outgroup to the African schistosomes, a single most-parsimonious tree was obtained of length 64 steps with a consistency index of 1. S. hippopotami was the sister-group to the remaining African species. This species has lateral-spined eggs and its basal position in the tree suggests that this condition is primitive and that terminal-spined eggs developed secondarily. Molecular data clearly show that S. hippopotami cannot be considered synonymous with S. mansoni. Assuming the hippopotamus is the normal host of S. hippopotami, phylogenetic analysis is consistent with an ancient association between schistosomes and ungulates. 相似文献
76.
Summary Microsomal and soluble fractions of Pleurotus pulmonarius exhibited a reduced carbon monoxide difference spectrum with P450 maxima at 448nm and 450–452nm respectively. Substrate induced Type I spectra were observed on addition of benzo(a)pyrene to both fractions. Benzo(a)pyrene hydroxylation was measured using the aryl hydrocarbon hydroxylase assay and was observed to be P450 dependent as indicated by carbon monoxide inhibition together with the substrate binding characteristics. The activity of the fractions were observed to give Km of 200mM and 660mM and Vmax of 1.25 nmol/min/nmol P450 and 0.57 nmol/min/nmol P450 for the microsomal and cytosolic fractions respectively. 相似文献
77.
Epithelial layer formation in differentiating aggregates of F9 embryonal carcinoma cells 总被引:16,自引:7,他引:9 下载免费PDF全文
F9 embryonal carcinoma (EC) cells, cultured in suspension in medium containing 5 X 10(-8) M retinoic acid, aggregate and differentiate into embryoid bodies with an outer layer of visceral endoderm cells that synthesize and secrete alphafetoprotein (AFP) (Hogan, B. L. M., A. Taylor, and E. Adamson, 1981, Nature (Lond.). 291:235-237). Here we analyze the formation of the outer layer of cells as a model for epithelial differentiation. Three morphological phases are described, but analyses of cell numbers and the synthetic rates of some proteins, as well as the appearance of markers of visceral endoderm and basement membrane, show that the formation of the outer layer occurs as an orderly progression of multiple events. The markers used to follow the ontogeny of epithelial layer formation include SSEA-1, l, and i blood group antigens, laminin, fibronectin, type IV collagen, cytoskeletal intermediate filament proteins (vimentin, Endo A, and B), and AFP. The onset of epithelium formation occurs between the third and fourth day of culture, but its function is maximally expressed only when it is well organized. We found the rate of AFP secretion to be a measure of the proper alignment and maturity of the epithelium which occurs at the seventh or eighth day. This model of epithelium formation may help to explain how similar processes occur during embryogenesis. 相似文献
78.
79.
The Egr-1 (zfp-6) gene encodes a zinc-finger-containing nuclear protein that is rapidly and transiently induced in quiescent cells treated with mitogens. We have constructed baculovirus vectors that synthesize mouse Egr-1 protein initiating at two putative ATG start sites. The ATG site producing the larger protein (Mr, 80,000) is similar, if not identical, to Egr-1 synthesized by serum-stimulated quiescent mouse fibroblasts, thus identifying the likely site for translation. The protein synthesized by the insect cells is active as assayed by its ability to bind to a specific DNA sequence that has been identified as an Egr-1 binding site. The insect cell system will allow further studies of the structure and function of the Egr-1 product, a protein that appears to be an important "master switch" for other genes. 相似文献