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The mean absolute deviation is also a measure of the variability of data in a sample. It is the absolute value of the average difference between the data values and the mean.
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The absolute value is a mathematical tool that represents the distance of a number from zero on the number line, regardless of its sign. In the context of inequalities, absolute value expressions help define a range of permissible values or boundaries for a variable. These inequalities are commonly used in scientific modeling and data interpretation, where variability within or beyond a certain threshold must be captured precisely.An absolute value inequality of the form ∣x∣ ≤...
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Absolute Copy Numbers of β-Actin Proteins Collected from 10,000 Single Cells.

Beiyuan Fan1,2, Xiufeng Li3,4, Lixing Liu5,6

  • 1State Key Laboratory of Transducer Technology, Institute of Electronics, Chinese Academy of Sciences, Beijing 100190, China. fanbeiyuan@ucas.ac.cn.

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|November 15, 2018
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Summary

Single-cell analysis reveals significant cell-to-cell variation in beta-actin (β-actin) protein levels within the same cell type. These findings question the reliability of β-actin as a consistent internal control in western blot experiments.

Keywords:
microfluidicspolymeric microfluidic flow cytometrysingle-cell analysissingle-cell protein quantification

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Area of Science:

  • Cell Biology
  • Biochemistry
  • Proteomics

Background:

  • Semi-quantitative studies show variable beta-actin (β-actin) protein expression at the population level.
  • The role of β-actin as an internal control in western blots is questioned due to inconsistent expression.
  • Absolute quantification of β-actin at the single-cell level is lacking.

Purpose of the Study:

  • To quantify the absolute copy numbers of β-actin proteins at the single-cell level.
  • To assess the variability of β-actin expression within and between different cell types.
  • To evaluate the suitability of β-actin as an internal control in western blotting.

Main Methods:

  • Utilized polymeric microfluidic flow cytometry for single-cell analysis.
  • Quantified absolute copy numbers of single-cell β-actin proteins in A549, Hep G2, and HeLa cells.
  • Employed neural network analysis to classify cell types based on β-actin expression.

Main Results:

  • Absolute β-actin copy numbers per cell were quantified: A549 (9.9 ± 4.6 × 10⁵), Hep G2 (6.8 ± 4.0 × 10⁵), and HeLa (11.0 ± 5.5 × 10⁵).
  • High coefficients of variation (~50%) and quartile coefficients of dispersion (~30%) indicated significant intra-cell type variability.
  • Low p-values (≪0.01) and high neural network classification rates (~70%) demonstrated significant inter-cell type expression differences.

Conclusions:

  • β-actin protein expression exhibits significant cell-to-cell variation within the same cell type.
  • Distinct differences in β-actin expression exist among A549, Hep G2, and HeLa cell types.
  • The inherent variability strongly questions the use of β-actin as a reliable internal control in western blots.