共查询到20条相似文献,搜索用时 15 毫秒
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Post-transcriptional regulation of ribosome accumulation during myoblast differentiation 总被引:3,自引:0,他引:3
The synthesis, accumulation and stability of rRNA were examined in embryonic quail myoblasts differentiating in cell culture. Quail myoblasts initially divide rapidly in culture, and accumulate 28S and 18S rRNA and ribosomes at a rate which maintains a constant ribosome content during cell division. After these myoblasts fuse, cell division ceases and ribosomes accumulate in fibers, but at a reduced rate which is only one fourth that in dividing myoblasts. Measurements of rRNA stability by 3H-methyl-methionine pulse-chase analysis show that 28S and 18S rRNA formed by fibers turn over with half-lives of 45 hr, and rRNA formed by myoblasts remains stable until fusion and then also turns over in fibers. Turnover of rRNA in fibers accounts for only half the reduction in ribosome accumulation following myoblast fusion. Measurements of the incorporation of 3H-adenosine into rRNA and ATP pools show that the rates of synthesis of rRNA precursor do not decrease after myoblast fuse, but half the rRNA molecules synthesized by fibers are degraded during processing. Degradation of rRNA during processing reduces the rate of formation of 28S and 18S rRNA, and together with rRNA turnover quantitatively accounts for the reduced rate of ribosome accumulation in fibers. 相似文献
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Control of cell differentiation during proliferation. I. Monocytic differentiation of HL-60 promyelocytes 总被引:1,自引:0,他引:1
The cell proliferation relating an uncommitted precursor cell to a differentiated terminal cell has been quantitated. HL-60 promyelocytes, a bipotent precursor cell capable of differentiating along either the myeloid or monocytic pathway, were induced by a human lymphocyte-conditioned medium (CM) to differentiate into macrophage-like cells. The promyelocytes had a generation time of approx. 42 h. Most promyelocytes which differentiated became macrophage-like cells after only one cell division. Some, a minority, underwent more than one division. The time between induction of differentiation and expression of differentiated characteristics could thus be very short. Labelled S-phase promyelocytes could differentiate after traversing S. G2 and undergoing mitosis. Some, approx. 21%, required a subsequent complete cell cycle before differentiating. The data suggest a model in which cells must undergo a S-phase-specific differentiation control event in the presence of CM in order to differentiate in the subsequent G1 phase. This model proposes that a discrete time in S phase exists when cells are susceptible to exogenous regulation directing them to yield differentiated daughter cells. 相似文献
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N Takahashi T R Breitman T Saito A Ichikawa 《The Journal of biological chemistry》1989,264(26):15624-15627
The human promyelocytic leukemia cell line HL60 differentiates to monocyte/macrophage cells when incubated with NADPH-linked high-Km aldehyde reductase (EC 1.1.1.2) purified from the cytosol of rat kidney. Differentiation was assessed by cell growth, morphology, adhesiveness, nitro blue tetrazolium reduction, and nonspecific esterase activity. The extent of differentiation induced by the reductase and measured at 4 days by nitro blue tetrazolium reduction is dose-dependent with an ED50 (dose required for half-maximal effect) of 71 nM. In the presence of 10 nM retinoic acid the ED50 for reductase is reduced to 18 nM and an isobologram analysis of this effect indicates that the combination is synergistic. Inactivation of the enzymatic activity is not associated with a decrease in differentiation-induced activity. These results suggest that the structure of the enzyme protein and not its enzymatic activity is involved with induction of differentiation. This view is supported by the demonstration that aldehyde reductase binds specifically to HL60 cells with a KD of 70 nM and that there are 13,000 binding sites/cell. Thus, the extent of differentiation induced by various concentrations of aldehyde reductase are directly related to the expected level of receptor occupancy. 相似文献
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