Graded transcriptional response to different concentrations of a single transactivator

Abstract

Threshold mechanisms of transcriptional activation are thought to be critical for translating continuous gradients of extracellular signals into discrete all-or-none cellular responses, such as mitogenesis and differentiation. Indeed, unequivocal evidence for a graded transcriptional response in which the concentration of inducer directly correlates with the level of gene expression in individual eukaryotic cells is lacking. By using a novel binary tetracycline regulatable retroviral vector system, we observed a graded rather than a threshold mechanism of transcriptional activation in two different model systems. When polyclonal populations of cells were analyzed at the single cell level, a dose-dependent, stepwise increase in expression of the reporter gene, green f luorescent protein (GFP), was observed by f luorescence-activated cell sorting. These data provide evidence that, in addition to the generally observed all-or-none switch, the basal transcription machinery also can respond proportionally to changes in concentration of extracellular inducers and trancriptional activators.

Modulation of cell cycle by graded expression of MLL-AF4 fusion oncoprotein

“…[29][30][31] Flow cytometric analysis of the representative clone D7 grown 96 h at varying tetracycline concentration confirmed a modulating effect of the MLL-AF4 expression levels on cell cycle progression. Cells cultured without tetracycline and therefore expressing MLL-AF4 at maximal level had one-half of the S phase redistributed in the G1 phase of the cell cycle then compared to nonexpressing cells grown at 1 mg/ml tetracycline (Figure 2).…”

Cotransduction of nondividing cells using lentiviral vectors

“…A potential superinfecting virus is thus thwarted by the receptor down-regulation. Thus, while sequential transductions can be used to deliver transgenes into single cells, 32 receptor interference apparently precludes the use of two amphotropic viruses to transduce single cells simultaneously. 7 Our use of vsvg-pseudotyped vectors derived from the documentation of Walker et al, 7 from the observation that vsvg-mediated entry is receptor independent, 33 and from our hypothesis that use of vsvg pseudotyping would allow simultaneous cotransduction into single cells.…”

Adeno-associated viral vector-mediated hypoxia-regulated VEGF gene transfer promotes angiogenesis following focal cerebral ischemia in mice

“…Several inducible promoters have been used to control gene expression, such as tetracycline operons, RU 486, edyasone and other inducible systems. [18][19][20][21][22][23][24][25] For the treatment of ischemic diseases, an ideal control would be the expression of angiogenic factors responding to hypoxia/ischemic. Hypoxia-inducible factor-1 (HIF-1) is a protein that accumulates in the tissue under hypoxic/ ischemia conditions.…”