Cell Systems
Volume 6, Issue 2, 28 February 2018, Pages 230-244.e1
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Article
GeneGini: Assessment via the Gini Coefficient of Reference “Housekeeping” Genes and Diverse Human Transporter Expression Profiles

https://doi.org/10.1016/j.cels.2018.01.003Get rights and content
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Highlights

  • Gini index (0–1) is a convenient means of summarizing inequalities of distribution

  • We apply it to two, large transcriptome datasets from tissues and cell lines

  • Membrane transporters (SLCs) have unusually heterogeneous distributions

  • Low Gini index transcripts make great reference genes; we describe many new ones

Summary

The expression levels of SLC or ABC membrane transporter transcripts typically differ 100- to 10,000-fold between different tissues. The Gini coefficient characterizes such inequalities and here is used to describe the distribution of the expression of each transporter among different human tissues and cell lines. Many transporters exhibit extremely high Gini coefficients even for common substrates, indicating considerable specialization consistent with divergent evolution. The expression profiles of SLC transporters in different cell lines behave similarly, although Gini coefficients for ABC transporters tend to be larger in cell lines than in tissues, implying selection. Transporter genes are significantly more heterogeneously expressed than the members of most non-transporter gene classes. Transcripts with the stablest expression have a low Gini index and often differ significantly from the “housekeeping” genes commonly used for normalization in transcriptomics/qPCR studies. PCBP1 has a low Gini coefficient, is reasonably expressed, and is an excellent novel reference gene. The approach, referred to as GeneGini, provides rapid and simple characterization of expression-profile distributions and improved normalization of genome-wide expression-profiling data.

Keywords

drug transporters
cell atlas
Gini index
SLCs
housekeeping genes
Human Protein Atlas
transcriptome
tissue specificity

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