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Inherent characteristics of gene expression for buffering environmental changes without the corresponding transcriptional regulations

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ABSTRACT

Gene expression patterning is crucial for environmental nutritional responses such as the nitrogen response in Escherichia coli. The nitrogen response is primarily regulated by the expression of glutamine synthetase (GS), which catalyzes the sole reaction of glutamine formation, by cis-logic regulatory circuits. Here, by removing the entire corresponding operator and promoter regions required for the control of GS, we constructed an E. coli strain that enables the detection of the basal GS gene expression, which is expressed from a plain promoter unrelated to the nitrogen response, and measured by co-transcribed GFP expression, an indicator of GS expression. Using strain cultures, we found that the GS expression level was able to shift inversely against the change of the environmental glutamine concentration. As a control experiment, we repeated similar experiments with another strain in which the GS regulatory region remained intact and the GFP gene following the plain promoter was introduced into a different chromosomal site. For this strain, we found that the GFP expression level did not shift in accordance with the environmental glutamine concentration. These results showed that GS expression from the plain promoter exhibited a responsive ability to buffer environmental changes, whereas the GS expression shift did not correlate with the specific characteristics of the plain promoter and GFP expression. This study identifies the inherent characteristics of basal gene expression in response to environmental changes, facilitating a deeper understanding of cellular design principles.

No MeSH data available.


Cell-cell variation of isogenic cells at final serial-transfer subculture grown on medium D with 5 mM glutamine or without glutamine (i.e., 0 mM glutamine). (A) Scattering data with two parameters between FS and FL signals measured by a flow cytometer. (B) The distribution of GFP concentration calculated by dividing the FL by FS signal. GFP concentration values are in arbitrary units (a.u.).
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f3-2_63: Cell-cell variation of isogenic cells at final serial-transfer subculture grown on medium D with 5 mM glutamine or without glutamine (i.e., 0 mM glutamine). (A) Scattering data with two parameters between FS and FL signals measured by a flow cytometer. (B) The distribution of GFP concentration calculated by dividing the FL by FS signal. GFP concentration values are in arbitrary units (a.u.).

Mentions: Among the serial-transfer cultures, we analyzed the cells in the final subculture with a flow cytometer and measured the forward scatter (FS) and GFP fluorescence (FL) signals (Fig. 3A). The FS and FL signals represent the size25 and GFP content of each cell, respectively. In addition, the GFP concentration in a cell was estimated by dividing the FL by the FS signal (Fig. 3B). We found that each cell had differences in the FS and FL signals, indicating the existence of a variation in cell size and GFP content. Through the serial-transfer cultures, the distribution pattern of the GFP concentration in cells became constant (data not shown). Recent experimental studies have revealed that stochastic effects force cells to show a cell-cell variation in gene expression, even in isogenic populations15,26,27. Thus, cell-cell variation seems to be naturally observed in cultured E. coli cells.


Inherent characteristics of gene expression for buffering environmental changes without the corresponding transcriptional regulations
Cell-cell variation of isogenic cells at final serial-transfer subculture grown on medium D with 5 mM glutamine or without glutamine (i.e., 0 mM glutamine). (A) Scattering data with two parameters between FS and FL signals measured by a flow cytometer. (B) The distribution of GFP concentration calculated by dividing the FL by FS signal. GFP concentration values are in arbitrary units (a.u.).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5036647&req=5

f3-2_63: Cell-cell variation of isogenic cells at final serial-transfer subculture grown on medium D with 5 mM glutamine or without glutamine (i.e., 0 mM glutamine). (A) Scattering data with two parameters between FS and FL signals measured by a flow cytometer. (B) The distribution of GFP concentration calculated by dividing the FL by FS signal. GFP concentration values are in arbitrary units (a.u.).
Mentions: Among the serial-transfer cultures, we analyzed the cells in the final subculture with a flow cytometer and measured the forward scatter (FS) and GFP fluorescence (FL) signals (Fig. 3A). The FS and FL signals represent the size25 and GFP content of each cell, respectively. In addition, the GFP concentration in a cell was estimated by dividing the FL by the FS signal (Fig. 3B). We found that each cell had differences in the FS and FL signals, indicating the existence of a variation in cell size and GFP content. Through the serial-transfer cultures, the distribution pattern of the GFP concentration in cells became constant (data not shown). Recent experimental studies have revealed that stochastic effects force cells to show a cell-cell variation in gene expression, even in isogenic populations15,26,27. Thus, cell-cell variation seems to be naturally observed in cultured E. coli cells.

View Article: PubMed Central - PubMed

ABSTRACT

Gene expression patterning is crucial for environmental nutritional responses such as the nitrogen response in Escherichia coli. The nitrogen response is primarily regulated by the expression of glutamine synthetase (GS), which catalyzes the sole reaction of glutamine formation, by cis-logic regulatory circuits. Here, by removing the entire corresponding operator and promoter regions required for the control of GS, we constructed an E. coli strain that enables the detection of the basal GS gene expression, which is expressed from a plain promoter unrelated to the nitrogen response, and measured by co-transcribed GFP expression, an indicator of GS expression. Using strain cultures, we found that the GS expression level was able to shift inversely against the change of the environmental glutamine concentration. As a control experiment, we repeated similar experiments with another strain in which the GS regulatory region remained intact and the GFP gene following the plain promoter was introduced into a different chromosomal site. For this strain, we found that the GFP expression level did not shift in accordance with the environmental glutamine concentration. These results showed that GS expression from the plain promoter exhibited a responsive ability to buffer environmental changes, whereas the GS expression shift did not correlate with the specific characteristics of the plain promoter and GFP expression. This study identifies the inherent characteristics of basal gene expression in response to environmental changes, facilitating a deeper understanding of cellular design principles.

No MeSH data available.