Cited by 85Single-cell and spatial transcriptomicsGene Regulatory Network AnalysisGene expression and cancer classification

Geometry of the Gene Expression Space of Individual Cells

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Korem, Yael, Szekely, Pablo, Hart, Yuval, Sheftel, Hila, Hausser, Jean, Mayo, Avi, Rothenberg, Michael E., Kalisky, Tomer +1 more·2015·PLOS Computational Biology

Abstract

There is a revolution in the ability to analyze gene expression of single cells in a tissue. To understand this data we must comprehend how cells are distributed in a high-dimensional gene expression space. One open question is whether cell types form discrete clusters or whether gene expression forms a continuum of states. If such a continuum exists, what is its geometry? Recent theory on evolutionary trade-offs suggests that cells that need to perform multiple tasks are arranged in a polygon or polyhedron (line, triangle, tetrahedron and so on, generally called polytopes) in gene expression space, whose vertices are the expression profiles optimal for each task. Here, we analyze single-cell data from human and mouse tissues profiled using a variety of single-cell technologies. We fit the data to shapes with different numbers of vertices, compute their statistical significance, and infer their tasks. We find cases in which single cells fill out a continuum of expression states within a polyhedron. This occurs in intestinal progenitor cells, which fill out a tetrahedron in gene expression space. The four vertices of this tetrahedron are each enriched with genes for a specific task related to stemness and early differentiation. A polyhedral continuum of states is also found in spleen dendritic cells, known to perform multiple immune tasks: cells fill out a tetrahedron whose vertices correspond to key tasks related to maturation, pathogen sensing and communication with lymphocytes. A mixture of continuum-like distributions and discrete clusters is found in other cell types, including bone marrow and differentiated intestinal crypt cells. This approach can be used to understand the geometry and biological tasks of a wide range of single-cell datasets. The present results suggest that the concept of cell type may be expanded. In addition to discreet clusters in gene-expression space, we suggest a new possibility: a continuum of states within a polyhedron, in which the vertices represent specialists at key tasks.

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  • Some facets of cellular identity are transient in time and space, and temporal processes may progress along trajectories, oscillate, or be influenced by spatial position.

    “First, in contexts such as development and physiology, some facets of cellular identity are transient in time and space. Temporal processes may, for example, progress along one or more trajectories (e.g., differentiation); oscillate continuously between cellular states (e.g., the cell cycle98,99 or circadian rhythm100); or be influenced by the physical position and neighborhood of the cell71,93.”
  • Removing the cell cycle's impact altogether may eliminate important facets of biological variation, for example in differentiation.

    “On the other hand, removing its impact altogether (e.g., regressing it out) may eliminate important facets of biological variation, for example, in differentiation processes98.”

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  1. SC Bendall, 2014, Single-cell trajectory detection uncovers progression and regulatory coordination in human B cell development, Cell, 157, 714, 10.1016/j.cell.2014.04.005 · DOI · Paper page
  2. SC Bendall, 2011, Single-Cell Mass Cytometry of Differential Immune and Drug Responses Across a Human Hematopoietic Continuum, Science, 332, 687, 10.1126/science.1198704 · DOI · Paper page

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Authors
Korem, Y., Szekely, P., Hart, Y., Sheftel, H., Hausser, J., Mayo, A., Rothenberg, M. E., Kalisky, T., & Alon, U.
Affiliations
  • Weizmann Institute of Science (IL)
  • Institute for Stem Cell Biology and Regenerative Medicine (US)
Corresponding author
Alon, Uri
Venue
PLOS Computational Biology
Published
2015-07-10
Volume
11
Issue
7
Pages
e1004224
ISSN
  • 1553-734X (ISSN-L)
  • 1553-7358
OpenAlex
W813853026
Cited by
85
References
103
Citations by year
2026: 9 · 2025: 12 · 2024: 4 · 2023: 6 · 2022: 6 · 2021: 7 · 2020: 10 · 2019: 8 · 2018: 10 · 2017: 7 · 2016: 5 · 2015: 1
FWCI
3.33
Type
journal article
Language
en
Open access
Locations
  • PLoS Computational Biology (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • RePEc: Research Papers in Economics (submittedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
  • Figshare (submittedVersion, cc-by)
Funders
  • Israel Cancer Association (3-10146, 1902/12, 20150911, 2017/13, 1634/13)
  • Israel Science Foundation (1634/13, 2017/13, 1902/12)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Single-cell and spatial transcriptomics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Gene Regulatory Network Analysis
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Gene expression and cancer classification
Keywords
single-cell transcriptomics, polytopes, evolutionary trade-offs, intestinal progenitor cells, dendritic cells, stemness, cell differentiation, spleen, bone marrow, intestinal crypt cells
MeSH terms
Animals, Cell Differentiation, Cells, Cultured, Computer Simulation, Gene Expression Regulation, Humans, Models, Biological, Proteins, Models, Statistical, Mice, Spatio-Temporal Analysis

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