Cited by 75Bioinformatics and Genomic NetworksGene Regulatory Network AnalysisComplex Network Analysis Techniques

Mapping the multiscale structure of biological systems

Open access
Schaffer, Leah V., Ideker, Trey·2021·Cell Systems

Abstract

Biological systems are by nature multiscale, consisting of subsystems that factor into progressively smaller units in a deeply hierarchical structure. At any level of the hierarchy, an ever-increasing diversity of technologies can be applied to characterize the corresponding biological units and their relations, resulting in large networks of physical or functional proximities-e.g., proximities of amino acids within a protein, of proteins within a complex, or of cell types within a tissue. Here, we review general concepts and progress in using network proximity measures as a basis for creation of multiscale hierarchical maps of biological systems. We discuss the functionalization of these maps to create predictive models, including those useful in translation of genotype to phenotype, along with strategies for model visualization and challenges faced by multiscale modeling in the near future. Collectively, these approaches enable a unified hierarchical approach to biological data, with application from the molecular to the macroscopic.

AI snapshot

Written from the paper’s full text.

TL;DR

This review argues that biological systems are deeply hierarchical and that pairwise proximity networks across scales can be used to build multiscale hierarchical maps. It surveys methods for constructing, functionalizing, visualizing, and evaluating these maps, from molecular to organismal scales.

Key findings

  • Proximity networks provide a general data structure across biological scales: atoms/residues via crystallography, cryo-EM, and cross-linking MS; proteins via AP-MS, co-elution, yeast two-hybrid, and proximity labeling; DNA via 3C/Hi-C; cells via single-cell RNA sequencing; and tissues/organs via anatomical or functional proximity.
  • Multiscale maps are built by detecting communities at multiple scales and tracing containment relations into a directed acyclic graph; examples include human interactome analysis that split the proteasome into catalytic and regulatory subunits plus kinetochore components, a yeast genetic interaction screen identifying ~1 million interactions, and a yeast histone H3-H4 structure inferred from 350 mutations crossed against 1370 gene deletions.
  • Data-driven hierarchies can be aligned with curated ontologies such as GO, CL, and HPO; NeXO and Mashup efforts recovered the majority of GO cellular components from protein network communities, while unmatched systems may represent novel discoveries.
  • Functionalized multiscale models can guide genotype-to-phenotype prediction and interpretable machine learning, including DCell, DrugCell, and hierarchy-aware function prediction; visualization approaches include DAG-to-tree transformations, circle-packing diagrams, and spatial overlays.

Methods

  • Design: a review and conceptual synthesis, not a primary experimental or computational study.
  • Data or sample: no new dataset; the paper surveys published literature and cited examples across molecular, cellular, tissue, and organismal scales.
  • Main analysis: organizes the field around proximity networks, community detection and hierarchical map construction, ontology alignment, functionalization, visualization, and outstanding challenges.

Limitations

  • Paper-stated: multiscale modeling faces unresolved challenges in choosing the optimal number of communities and hierarchy levels, evaluating models, integrating diverse data modalities, capturing dynamics and context dependence, and broadening beyond one-gene-per-node representations to include protein diversity and small molecules.
  • Evident from the text: as a review, it provides no original empirical validation or quantitative benchmarking of the discussed methods; its claims depend on the cited primary studies.

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Integrity signals

Registry

Crossref · 10.1016/j.cels.2021.05.012

Cites

161 of 161 references verified0 citation errors · 0 not checkable

Statistics

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Claims the paper makes

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  • Premisecitation

    Braberg et al. converted similarities between mutational profiles into an upper bound on distance between mutational residues to create multiscale models of protein complex structures.

    “In another recent study, similarities between mutational profiles were converted into an upper bound on distance between mutational residues to create multiscale models of protein complex structures (Braberg et al., 2020).”
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    There is a notable relation between multiscale hierarchies and biological ontologies, in which a biological entity or concept is recursively factored into a set of subconcepts, sub-subconcepts, and so on.

    “There is a notable relation of the multiscale hierarchies described above and biological ontologies, in which a biological entity or concept is recursively factored into a set of subconcepts, sub-subconcepts, and so on (Gruber, 1995).”
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  • Interpretationreasoning

    Networks provide a core foundation for representing many types of experimental evidence across many scales in the inference of biological structure and function.

    “Thus, networks provide a core foundation for representing many types of experimental evidence – across many different scales – in the inference of biological structure and function.”
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    Many measurement techniques underlying structural, systems, and developmental biology are based on observations of pairwise proximity, which are naturally represented by biological proximity networks.

    “Importantly, many of the measurement techniques underlying structural, systems, and developmental biology are based on observations of pairwise proximity, which are naturally represented by biological “proximity” networks.”
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    Single-cell RNA sequencing can generate cell-cell networks in which nodes represent the RNA expression state of individual cells and edges connect pairs of highly similar cells.

    “Above the level of individual proteins and genomic loci, many recent studies use the technique of single-cell RNA sequencing to generate cell-cell networks, in which nodes represent the RNA expression state of an individual cell, and edges connect pairs of cells that are highly similar (Bendall et al., 2014; Trapnell et al., 2014).”
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    Premisecitation

    It is a challenge in single-cell analyses to deconvolve the relationship between cell type and time, resulting in the development of a diversity of algorithms to infer the trajectory of cell differentiation across time.

    “it is a challenge in single-cell analyses to deconvolve the relationship between cell type and time, resulting in the development of a diversity of algorithms to infer the trajectory of cell differentiation across time (Saelens et al., 2019).”
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    Hi-C records pairs of genomic loci at close proximity, and certain pairs emerge close in three dimensions although separated at large nucleotide distances along the linear chromosome.

    “Moving from proteins to DNA, the family of techniques known as chromosome conformation capture, including 3C (Dekker et al., 2002) and Hi-C (Lieberman-Aiden et al., 2009), record pairs of genomic loci that are at close proximity.”
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    Premisecitation

    Genetic interactions can be observed among genes participating in distinct parallel biological pathways, so genes with similar genetic interaction profiles do not always encode proteins in close physical proximity.

    “Although genes with similar genetic interaction profiles can encode proteins in close physical proximity, this does not always have to be the case, as genetic interactions can also be observed among genes participating in distinct parallel biological pathways (Gonatopoulos-Pournatzis et al., 2020).”
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    The community detection approach was well illustrated in recent analyses of protein-protein interaction networks in yeast and human.

    “The community detection approach was well illustrated in recent analyses of protein-protein interaction networks in yeast (Dutkowski et al., 2013) and human (Huttlin et al., 2015).”
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    Premisecitation

    Amino-acid proximity networks are central to many efforts to model protein structure and to protein structure prediction.

    “Such amino-acid proximity networks, whether experimentally generated or inferred, are central to many efforts to model protein structure. They are also central to protein structure prediction.”
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    Premisecitation

    Cell-cell similarity networks from single-cell RNA sequencing can be analyzed to track cell developmental trajectories over time or to recognize groups of cells forming a distinct cell type or tissue.

    “The resulting cell-cell similarity network can then be analyzed to track cell developmental trajectories over time (Farrell et al., 2018; Wagner et al., 2018; Zhong et al., 2018) or to recognize groups of cells forming a distinct cell type or tissue (Jaitin et al., 2014; Zeisel et al., 2015).”
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    Premisecitation

    Developing a multiscale representation requires analyzing communities in biological networks at more than one scale, defining and identifying communities at each scale, and tracing containment to infer a hierarchical map.

    “Developing a multiscale representation requires analyzing communities in biological networks at more than one scale. Communities (clusters of highly interconnected nodes) are first defined and identified at each of multiple scales; subsequently, communities that are contained within other communities, in whole or in part, can be traced to infer a hierarchical map (Figure 2) (Dotan-Cohen et al., 20”
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    The Mashup algorithm analyzes the topology of each network separately and learns a single weighted network representation that best explains the topological patterns observed across all networks.

    “In a related method, the Mashup algorithm analyzes the topology of each network separately and learns a single weighted network representation that best explains the topological patterns observed across all networks (Cho et al., 2016).”
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    Premisereasoning

    Once multiple datasets have been combined into a unified network, community detection algorithms may be run on this network to build hierarchical maps.

    “Once the data have been combined into a unified network, community detection algorithms may then be run on this network to build hierarchical maps as described above.”
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    Premisenone given

    At any level of the biological hierarchy, an ever-increasing diversity of technologies can characterize biological units and their relations, yielding large networks of physical or functional proximities.

    “At any level of the hierarchy, an ever-increasing diversity of technologies can be applied to characterize the corresponding biological units and their relations, resulting in large networks of physical or functional proximities”
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    Premisecitation

    In the human protein interaction study, clique percolation determined high-level protein communities, and modularity-based clustering subdivided them into more granular subsystems, resulting in a multi-layer hierarchical structure.

    “In the human study, the authors first performed clique percolation to determine high-level protein communities; subsequently, they ran modularity-based clustering to further subdivide these communities into more granular subsystems, resulting in a multi-layer hierarchical structure (Figure 3A).”
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    Interpretationnone given

    Anatomical dissection results can be thought of as generating a network of tissue types interrelated by physical or functional proximity.

    “Finally, at the highest level in the structural hierarchy of an organism, results from anatomical dissection can be thought of as generating a network of tissue types interrelated to one another by physical or functional proximity.”
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    Premisereasoning

    There is an important tradeoff between conveying the complete information represented in the hierarchy and avoiding a graphic that is too complex to interpret or investigate.

    “In this common case, there is an important tradeoff between conveying the complete information represented in the hierarchy while avoiding a graphic that is too complex to interpret or investigate.”
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    Premisecitation

    In the DCell study, the structure of a deep neural network was constrained to mirror the hierarchy of cellular components recorded by GO or a multiscale map of cellular components derived from molecular interaction data, and DCell learned to translate genotype to phenotype and capture the functional state of cell subsystems throughout the hierarchy.

    “In this study, the structure of a deep neural network (i.e. configuration of artificial neurons) was constrained to mirror the hierarchy of cellular components recorded by GO or, alternatively, a multiscale map of cellular components derived from molecular interaction data. This model, called DCell, was able to learn not only to translate genotype to phenotype, but also to capture the functional”
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    Even with a multiscale model, translation of genotype to phenotype can be complex, and the use of standard black-box machine learning algorithms prevents straightforward biological interpretation.

    “Even with a multiscale model, the translation of genotype to phenotype can be complex, and the use of standard “black-box” machine learning algorithms prevents a straightforward biological interpretation (Rudin, 2019).”
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    Premisecitation

    Gaudelet et al. modeled a neural network structure on the multiscale functional organization of a cell by integrating gene-pathway annotations in the Reactome database, and their model accurately determined patient diagnoses based on gene expression data.

    “In a related study, Gaudelet et al. modeled a neural network structure on the multiscale functional organization of a cell by integrating gene-pathway annotations in the Reactome database; their model was able to accurately determine patient diagnoses based on gene expression data.”
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    Premisecitation

    Gaudelet et al. modeled pairwise protein interactions, complexes, and pathways as multiscale hypernetworks, and analysis of these hypergraphs resulted in determining protein function for many uncharacterized genes.

    “For example, Gaudelet et al. modeled pairwise protein interactions, complexes, and pathways as multiscale hypernetworks; analysis of these hypergraphs resulted in determining protein function for many uncharacterized genes (Gaudelet et al., 2018).”
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    Premisecitation

    The Ohmnet multiscale approach at the level of biological tissues enabled prediction of tissue-specific cellular functions for different proteins, outperforming competing methods that did not account for the multiscale hierarchical organization of tissues.

    “This multiscale approach at the level of biological tissues enabled prediction of tissue-specific cellular functions for different proteins, outperforming competing methods which did not account for the multiscale hierarchical organization of tissues.”
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    Premisereasoning

    Ontology alignment seeks to address the challenge of determining entities in different hierarchies that represent the same concept, including how to handle multiple overlapping entities and differences in ontology organization.

    “For this purpose, the area known as ”ontology alignment” seeks to address the challenge of determining entities in different hierarchies that represent the same concept, including how to handle multiple overlapping entities and differences in ontology organization.”
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    Premisereasoning

    Visualization of results as a hierarchy communicates the hierarchical relationships among subsystems across multiple levels.

    “While many applications of clustering and community detection show the detected communities as a flat list or network (Figure 3A), visualization of results as a hierarchy (Figure 5A) communicates the hierarchical relationships among subsystems across multiple levels.”
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    Premisecitation

    Yu et al. proposed an explicit hierarchical approach for translation of genotype to phenotype in which mutations were propagated upward through a hierarchy of cellular components and processes, and mutation states of entities were used as features to explain phenotype.

    “An explicit hierarchical approach for translation of genotype to phenotype was proposed by (Yu et al., 2016), in which mutations were propagated upward through a hierarchy of cellular components and processes. The mutation states of these entities (i.e. entities containing mutated genes) were then used as features to explain phenotype, enabling the appropriate scale in the cell to be used for”
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    Premisecitation

    Biological ontologies are large hierarchies with a DAG structure, so existing tools for visualizing ontologies can have direct application to data-driven multiscale models.

    “Biological ontologies are large hierarchies which also have a DAG structure; as such, existing tools for visualizing ontologies can also have direct application to data-driven multiscale models (Binns et al., 2009; Eden et al., 2009; Sealfon et al., 2006; Supek et al., 2011; Zhu et al., 2019).”
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    Interpretationreasoning

    Multiscale models have great potential for understanding function and predicting outcomes in biological systems, since knowledge of higher-order protein assemblies in which proteins participate provides evidence for their function and relevance to diseases.

    “Multiscale models have great potential for the applications of understanding function and predicting outcomes in biological systems, since knowledge of the higher-order protein assemblies in which proteins participate provides evidence for their function and relevance to particular diseases.”
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    Premisecitation

    Another study generated a multiscale hierarchical map from a co-expression network of a pathogenic fungus; this map was used to identify clusters in the hierarchy associated with plant cell infection, determining genes not previously reported to function in these pathways.

    “Another study generated a multiscale hierarchical map from a co-expression network of a pathogenic fungus; this map was used to identify clusters in the hierarchy associated with plant cell infection, determining genes not previously reported to function in these pathways (Ames, 2017).”
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    Interpretationreasoning

    Systems not found in GO may correspond to novel discoveries.

    “Conversely, systems not found in GO may correspond to novel discoveries.”
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    Premisecitation

    DrugCell is an interpretable deep learning model of cancer cell proliferation trained on the response of tumor cell lines to a large panel of drugs, combining genotype and drug structure to predict drug response along with specific cellular subsystems mediating that response.

    “This thread was recently extended through the development of DrugCell, an interpretable deep learning model of cancer cell proliferation (Kuenzi et al., 2020). Here, the model was trained on the response of tumor cell lines to a large panel of drugs, combining genotype and drug structure to predict the drug response along with the specific cellular subsystems mediating that response.”
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    Neural networks have been used to perform interpretable deep learning on biological networks to differentiate cell types and determine regulatory differences in single-cell RNA sequencing data.

    “Related work has used neural networks to perform interpretable deep learning on biological networks to differentiate cell types and determine regulatory differences in single cell RNA sequencing data (Fortelny and Bock, 2020).”
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    Premisecitation

    The Yu et al. hierarchical approach accurately predicted yeast growth phenotypes from pairwise deletions of non-essential yeast genes, determining affected areas in the hierarchy.

    “This hierarchical approach was used to accurately predict yeast growth phenotypes from pairwise deletions of non-essential yeast genes, determining affected areas in the hierarchy.”
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    Premisecitation

    Programs have been developed to analyze and visualize cross-linking data as a network of amino acid nodes, where edges represent a detected cross-link, and organizing clusters of nodes spatially according to subunit is one approach applied in these networks.

    “For example, programs have been developed to analyze and visualize cross-linking data as a network of amino acid nodes, where edges represent a detected cross-link (Combe et al., 2015; Courcelles et al., 2017; Grimm et al., 2015; Riffle et al., 2016); organizing clusters of nodes spatially according to subunit is one approach that has been applied in these networks (Figure 5C).”
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    Interpretationreasoning

    Genetic mutations may exert their effects at the level of the gene, the protein complex, or the broader pathway or organelle, and determining the relevant scale in the biological hierarchy can enable accurate prediction of phenotype.

    “For example, genetic mutations in a genotype may exert their effects at the level of the gene, the protein complex, or the broader pathway or organelle; determining the relevant scale in the biological hierarchy can enable accurate prediction of phenotype, revealing the importance of multiple scales in modeling biological function.”
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    Interpretationnone given

    Hierarchical multiscale representations have the major advantages of generality across analytical methods and their scales and a comprehensive scope.

    “On the other hand, the hierarchical multiscale representations have the major advantages of generality across analytical methods (and their scales) and a comprehensive scope (genome-wide, see Box 1).”
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    Premisecitation

    DeepGO used features from protein sequences and interactions to predict protein function; the features were used to build a hierarchical neural network classifier based on GO, so that predictions and features could be refined at each level of the biological hierarchy, resulting in a model optimized for function prediction.

    “DeepGO used features from protein sequences and interactions to predict protein function; the features were used to build a hierarchical neural network classifier based on GO, so that predictions and features could be refined at each level of the biological hierarchy, resulting in a model optimized for function prediction (Kulmanov et al., 2018).”
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    Premisecitation

    In the Yu et al. analysis, many genetic interactions were predicted within the oxidative phosphorylation subsystem; negative interactions occurred between the two subsystems of electron and protein transport, whereas positive interactions occurred solely within electron transport.

    “For example, many genetic interactions were predicted within the oxidative phosphorylation subsystem; negative interactions (worse than expected growth) occurred between the two subsystems of electron and protein transport, whereas positive interactions (better than expected growth) occurred solely within electron transport.”
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    One strategy for integrating hierarchical maps with spatial organization is to overlay the localization coordinates of each entity in 2D or 3D.

    “One strategy for integrating hierarchical maps with spatial organization is to overlay the localization coordinates of each entity in 2D or 3D.”
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    Premisecitation

    Clustering analysis of networks is sensitive to network noise, and biochemical experimental challenges as well as cell-to-cell variation can contribute to this issue.

    “Clustering analysis of networks is sensitive to network noise (Stacey et al., 2020), and biochemical experimental challenges as well as cell-to-cell variation can contribute to this issue.”
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    Community detection algorithms such as Louvain or Newman-Girvan determine the approximate number of communities by optimizing modularity, or the density of links within communities versus links between communities.

    “Community detection algorithms such as Louvain (Blondel et al., 2008) or Newman Girvan (Girvan and Newman, 2002) determine the approximate number of communities by optimizing modularity, or the density of links within communities versus links between communities.”
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    Premisecitation

    A complementary multiscale visualization strategy is to integrate 3D structural information with associated nodes in a hierarchy; software tools have been developed that display available 3D structural data for selected proteins and physical pairwise interactions in protein-protein interaction networks.

    “A complementary multiscale visualization strategy is to integrate 3D structural information with associated nodes in a hierarchy; software tools have been developed that display available 3D structural data for selected proteins and physical pairwise interactions in protein-protein interaction networks (Morris et al., 2007; Mosca et al., 2013; Nepomnyachiy et al., 2015).”
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    Premisereasoning

    Another well-known problem in community detection is the tradeoff between quality control and completeness, since not all biological entities of interest may be detected or meet a quality threshold due to experimental challenges.

    “Another well-known problem in community detection is the tradeoff between quality control and completeness, since not all biological entities of interest may be detected or meet a quality threshold due to experimental challenges.”
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    Premisenone given

    Various experimental data types and analytical methods generate networks of proximity between biological entities at different levels of the hierarchy and thus at different scales.

    “Various experimental data types and analytical methods generate networks of proximity between biological entities at different levels of the hierarchy and thus at different scales.”
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    Premisecitation

    Some approaches have used machine learning to integrate pairwise distance measurements at different scales.

    “Some approaches have used machine learning to integrate pairwise distance measurements at different scales (Qin et al., 2020)”
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    Many of the multiscale models described in the paper are presented as a static snapshot of biological structure.

    “While many of the multiscale models that have been described herein are presented as a static snapshot of biological structure”
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    Interpretationreasoning

    Collectively, these techniques provide the opportunity to create unified hierarchical models across multiple relevant biological scales, from the very small (angstroms) to the very large (meters).

    “Collectively, these techniques provide the opportunity to create unified hierarchical models across multiple relevant biological scales, from the very small (angstroms) to the very large (meters).”
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    Interpretationreasoning

    Collectively, these approaches enable a unified hierarchical approach to biological data, with application from the molecular to the macroscopic.

    “Collectively, these approaches enable a unified hierarchical approach to biological data, with application from the molecular to the macroscopic.”
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    Premisereasoning

    When performing community detection at multiple scales to develop a hierarchy, there is the additional challenge of determining a suitable number of levels for the hierarchy, as this number is also typically not known beforehand.

    “When performing community detection at multiple scales to develop a hierarchy, there is the additional challenge of determining a suitable number of levels for the hierarchy, as this number is also typically not known beforehand.”
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    Premisecitation

    Protein diversity, including sequence isoforms and post-translational modifications, controls interactions between proteins and individual protein function.

    “in reality protein diversity (including sequence isoforms and post-translational modifications) controls interactions between proteins and individual protein function (Aebersold et al., 2018).”
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    In integrative structural biology, data from multiple methods are collected and translated to spatial restraints, which are used in scoring sampled structures.

    “In integrative structural biology, data from multiple methods are collected and translated to spatial restraints, which are used in scoring sampled structures (Rout and Sali, 2019)”
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    Premisecitation

    Some approaches have used machine learning to integrate single cell data with context-independent data to create cell-type specific interactomes.

    “or to integrate single cell data with context-independent data to create cell-type specific interactomes (Mohammadi et al., 2019).”
    Quote in the paperNot a substantial claim0 of 1 sources checked
    • cites Mohammadi et al., 2019 source

      Not checked in the free run.

47 of 47
  • The authors state this as an assumption.

    Cells related in developmental lineage will have similar expression profiles.

    “under the assumption that cells related in developmental lineage will have similar expression profiles”
  • The paper relies on this without support.

    Cellular processes are highly dynamic, involving transient regulatory interactions and control of protein interactions via post-translational modifications.

    “cellular processes are highly dynamic, involving transient regulatory interactions and control of protein interactions via post-translational modifications.”
2 of 2

Claims other papers make about this one

Each is checked against this paper’s own text: does it say what the citing paper says it does?

Cites

Flagged first, then by citations

Research works printed but not linked: 1

  1. Qin, 2020, Mapping cell structure across scales by fusing protein images and interactions, bioRxiv

Cited by

Sorted by citations

Authors
Schaffer, L. V., & Ideker, T.
Affiliations
University of California San Diego (US)
Corresponding author
Ideker, Trey
Venue
Cell Systems
Publisher
Elsevier BV
Published
2021-06
Volume
12
Issue
6
Pages
622-635
ISSN
2405-4712 (ISSN-L)
OpenAlex
W3167882125
Cited by
75
References
161
Citations by year
2026: 14 · 2025: 28 · 2024: 16 · 2023: 9 · 2022: 6 · 2021: 2
FWCI
0.87
Type
journal article
Language
en
Open access
Locations
  • Cell Systems (publishedVersion)
  • PubMed (publishedVersion)
  • PubMed Central (acceptedVersion)
  • eScholarship (California Digital Library) (submittedVersion)
Funders
  • National Institutes of Health
  • National Human Genome Research Institute (HG009979)
  • National Institute of Environmental Health Sciences (ES014811)
  • University of California, San Diego
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Bioinformatics and Genomic Networks
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Gene Regulatory Network Analysis
  • Physical Sciences › Physics and Astronomy › Statistical and Nonlinear Physics › Complex Network Analysis Techniques
Keywords
multiscale biological systems, biological networks, protein structure, protein complexes, prediction model, model visualization, multiscale modeling
MeSH terms
Proteins, Systems Biology

About these checks

Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.

Claims read by deepseek-v4.1-flash under definition version 3 (extract-v3) on 2026-10-10.

Classified by jev-1.13-20260917 (gold-guideline-v0.2) on 2026-10-10.

Statistics and arithmetic are recomputed, not judged.

Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.

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