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51.
Glycosaminoglycans (GAG) are known to participate in central nervous system
processes such as development, cell migration, and neurite outgrowth, but
little is known with respect to their regulation through soluble
neurotrophic factors. In the present study, we have addressed this issue
using cell culture models of three distinct cell populations derived from
young rat retinas, namely, purified M uller glia, pigmented epithelium, and
neurons respectively. Cultures were maintained in chemically defined media
in the presence or absence of either basic fibroblast or epidermal growth
factor. In control glial and epithelial cultures, hyaluronic acid dominated
the soluble GAG pool, with lesser contributions from dermatan sulfate,
chondroitin sulfate, and heparan sulfate (in decreasing order). Retinal
neuronal GAG were almost exclusively chondroitin sulfate (approximately
90%). Treatment of glial and epithelial cultures with either factor led to
dose-dependent increases in especially hyaluronic acid synthesis (a maximum
6-fold increase relative to control levels), with smaller but consistent
changes in chondroitin sulfate. Similar treatment of retinal neurons did
not lead to any changes in GAG synthesis. These data indicate that glia and
pigment epithelia are the principal sources of GAG components in retina at
least in vitro, and that endogenous neurotrophic growth factors can greatly
modify GAG synthesis in these two retinal cell populations. Such data
suggest that a delicate balance may exist between growth factor
availability and glycoconjugate metabolism in vivo, participating in normal
or pathological states of the retina.
相似文献
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The technique of gene fusion, in which the gene of interest, severed from its 3' end, is in-phase fused to a reporter gene--usually lacZ--is widely used to study translational regulation in Escherichia coli. Implicit in these approaches is the assumption that the activity of the ribosome binding site (RBS) fused in-phase with lacZ, does not per se modify the steady-state level of the lacZ mRNA. Herein, we have tested this hypothesis, using a model system in which the RBS of the lamB gene is fused to lacZ. Several point mutations affecting translation initiation have been formerly characterized in this RBS, and we used Northern blots to study their effect upon the lacZ mRNA pattern. Two series of constructs were assayed: in the first one, a 51-bp fragment centered around the lamB initiator codon, was inserted in front of lacZ within the natural lactose operon, whereas in the second the lacZ gene was fused to the genuine malK-lamB operon just downstream from the lamB RBS. We observed that in the first series, the concentration and average molecular weight of the lacZ mRNA dropped sharply as the efficiency of the RBS decreased. This apparently arose from a decreased stability of the message, since the mRNA patterns are equalized when the endonuclease RNase E is inactivated. We suggest that in this case the rate limiting step in the decay process is an RNase E cleavage that is outcompeted by translation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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Culture conditions differentially affect the translation of individual Escherichia coli mRNAs. 总被引:4,自引:0,他引:4
Our aim is to investigate whether changes in growth conditions can differentially affect the initiation of translation from individual Escherichia coli mRNAs that are not subjected to specific translational control. As a model system, we have constructed a series of point-mutated lacZ genes which differ in their Shine-Dalgarno (SD) sequence, their initiator codon, or the secondary structure around these elements. Alterations in growth conditions produced large (up to 8-fold) changes in the relative expression from these genes, which, we argue, stem from changes in their relative efficiencies of translation initiation. In particular, compared to genes bearing mutations outside the SD or initiator codon, genes mutated in these elements experience a significant decrease in their expression when cells are grown in minimal rather than rich medium; at 42 degrees C rather than 37 degrees C; or under amino acid starvation. We discuss the mechanisms underlying these effects, and evocate their possible generality. 相似文献
58.
J L Huret H Mossafa A Brizard B Dreyfus F Guilhot X Q Xue P Babin J Tanzer 《Annales de génétique》1989,32(3):155-159
We report on 33 unpublished patients with clonal anomalies in chronic lymphocytic leukaemia. The literature was thoroughly reviewed in order 1) to quantify the frequency of anomalies found in chronic lymphocytic leukaemia and to give new status to the rarest, 2) to determine whether a given anomaly was an additional anomaly and/or a primary anomaly, and 3) to find out whether strong associations between different anomalies exist in this disease. 相似文献
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