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1.
Extracellular matrix organization modulates fibroblast growth and growth factor responsiveness 总被引:13,自引:0,他引:13
To learn more about the relationship between extracellular matrix organization, cell shape, and cell growth control, we studied DNA synthesis by fibroblasts in collagen gels that were either attached to culture dishes or floating in culture medium during gel contraction. After 4 days of contraction, the collagen density (initially 1.5 mg/ml) reached 22 mg/ml in attached gels and 55 mg/ml in floating gels. After contraction, attached collagen gels were well organized; collagen fibrils were aligned in the plane of cell spreading; and fibroblasts had an elongated, bipolar morphology. Floating collagen gels, however, were unorganized; collagen fibrils were arranged randomly; and fibroblasts had a stellate morphology. DNA synthesis by fibroblasts in contracted collagen gels was suppressed if the gels were floating in medium but not if the gels were attached, and inhibition was independent of the extent of gel contraction. Therefore, growth of fibroblasts in contracted collagen gels could be regulated by differences in extracellular matrix organization and cell shape independently of extracellular matrix density. We also compared the responses of fibroblasts in contracted collagen gels and monolayer culture to peptide growth factors including fibroblast growth factor, platelet-derived growth factor, transforming growth factor-beta, and interleukin 1. Cells in floating collagen gels were generally unresponsive to any of the growth factors. Cells in attached collagen gels and monolayer culture were affected similarly by fibroblast growth factor but not by the others. Our results indicate that extracellular matrix organization influenced not only cell growth, but also fibroblast responsiveness to peptide growth factors. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
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After dopachrome? 总被引:4,自引:0,他引:4
J M Pawelek 《Pigment cell research / sponsored by the European Society for Pigment Cell Research and the International Pigment Cell Society》1991,4(2):53-62
Dopachrome, an intermediate in melanin biosynthesis, exhibits some unusual properties. At physiologic pH (e.g., pH 6-8) it is unstable and spontaneously loses its carboxyl group to form 5,6-dihydroxyindole (DHI) and CO2. However, over this same pH range, if various metals or a melanocyte-specific enzyme are present, it rapidly rearranges to its isomer form--5,6-dihydroxyindole-2-carboxylic acid (DHICA)--which is far more stable than dopachrome in its ability to retain the carboxyl group. Whether or not the carboxyl group is retained could have important implications for the regulation of melanogenesis, since in the presence of oxygen DHI spontaneously forms a black precipitate, whereas DHICA forms a golden-brown solution. The solubility of "DHICA-melanin" is due to the presence of carboxyl groups, which provide negative charges and hydrophilicity. Thus, in vivo, the extent to which dopachrome is converted to DHI or DHICA may well influence the solubility and color of the melanin formed. The purpose of this article is to review recent findings in these areas and to discuss the possible significance of dopachrome conversion in the regulation of melanogenesis and color formation. 相似文献
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