Various cell types
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Understanding Various Cell Types: Definitions, Classifications, and Evolution
Evolutionary Definition of Cell Types
Cell types are fundamental units of multicellular organisms, exhibiting extensive diversity, especially in animals. Recent research proposes an evolutionary definition of cell types, emphasizing the role of the 'core regulatory complex' (CoRC) of transcription factors. These factors are crucial in distinguishing emergent sister cell types, enabling their independent evolution and regulating cell type-specific traits known as apomeres. This approach helps delineate and compare cell types within and between species, providing a clearer classification scheme1.
Conceptual Definitions in Mature Organisms
In mature organisms, cell types are traditionally viewed as hard-wired entities, each representing a unique endpoint of a developmental journey from a single fertilized oocyte. However, cells in established tissues can exist in different maturation and activation states and may even convert into other cell types within the same tissue. This dynamic nature suggests that cell types should be defined by both hard-wired characteristics and softer features such as morphology, gene expression patterns, location, function, and plasticity2.
Comprehensive Cell Taxonomy
The Cell Taxonomy repository offers a curated and comprehensive collection of cell types and associated markers across various species, tissues, and conditions. This resource integrates data from single-cell transcriptomic profiles, providing a well-structured taxonomy for over 3,000 cell types and housing a vast collection of associated markers. Such a repository is invaluable for understanding cellular heterogeneity, developmental processes, and tumorigenesis at a single-cell resolution3.
Human Cell Atlas and Ontologies
The Human Cell Atlas (HCA) project, involving over 2,000 scientists, has generated extensive molecular profiles of millions of single cells across multiple organs and systems. This effort has significantly advanced our understanding of cell types and states, particularly in fields like immunology and neuroscience. The HCA emphasizes the need for unified cell ontologies to harmonize and integrate diverse annotations, thereby consolidating and advancing our knowledge of cell types across scientific communities4.
Brain Cell Types and Taxonomy
The diversity of brain cell types has been a central focus in neuroscience. Despite advances in single-cell transcriptome and epigenome profiling, a complete taxonomy of brain cell types remains elusive. Defining brain cell types involves considering networks of genes and regulatory elements, emphasizing self-stabilizing regulation. Integrating data from molecular profiling, epigenetic landscapes, cellular morphology, connectivity, and physiology is essential for a meaningful definition of brain cell types5.
Periodic Table of Cell Types
A novel hypothesis proposes a 'periodic table of cell types' as a framework to distinguish cell types from cell states. This table aligns cell types according to their developmental stages, connecting them based on their differentiation trajectories. Such a framework could predict new cell types and states and recognize relationships between cell types throughout development and evolution6.
Cell Types as Species
The concept of cell types has been compared to the classification of species in systematics and evolutionary biology. Both fields grapple with defining entities that exhibit continuous variation rather than discrete categories. This metaphor highlights the parallels between cell type differentiation and species evolution, suggesting that models for evolutionary divergence could inform our understanding of cell type differentiation8.
Integrative Approaches to Cell Identity
Defining cell types requires integrating diverse single-cell measurements from multiple experiments and biological contexts. Algorithms like LIGER help delineate shared and dataset-specific features of cell identity, facilitating the analysis of complex datasets. Such integrative approaches are crucial for advancing our understanding of cell-type definition, gene regulation, and disease states10.
Conclusion
The study of cell types is a dynamic and evolving field, with significant advancements in defining and classifying cell types through evolutionary, conceptual, and integrative approaches. Resources like the Cell Taxonomy repository and projects like the Human Cell Atlas are pivotal in consolidating our knowledge and providing a comprehensive understanding of cellular diversity across species and tissues.
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The origin and evolution of cell types
Cell type identity is primarily determined by evolutionary changes in the core regulatory complex, which enable distinct sister cell types to emerge, evolve, and regulate specific traits.
Highly CitedWhat Is Your Conceptual Definition of "Cell Type" in the Context of a Mature Organism?
Cell type in the human body involves both hard-wired characteristics and softer features like morphology, gene expression pattern, location, function, and plasticity.
Rigorous JournalHighly CitedCell Taxonomy: a curated repository of cell types with multifaceted characterization
Cell Taxonomy is a comprehensive and curated repository of cell types and associated markers, aiding in understanding cellular biology in diverse species.
Cell type ontologies of the Human Cell Atlas
Human Cell Atlas data reveals a wide variety of cell types and states, highlighting the need for a unified cell ontology to consolidate and advance our understanding of cell types across scientific communities and biological domains.
Rigorous JournalHighly CitedPerspectives on defining cell types in the brain
A definition of brain cell type emphasizing self-stabilizing regulation is essential for a complete census and taxonomy of brain cell types, requiring integration of data from multiple modalities.
The definition of cell type.
Cell type definition is evolving, with systematic genomics accelerating this process and providing a more comprehensive understanding of blood vessel development and function.
Cell types as species: Exploring a metaphor
Cell types and species share parallels in philosophy, lineage structures, and evolutionary divergence, inspiring biologists to explore new solutions to similar problems in both fields.
What is a cell type?
Cell types in humans are assigned based on molecular features, but there is often phenotypic diversity among cells of the same type, raising the question: what is a human cell type?
Single-Cell Multi-omic Integration Compares and Contrasts Features of Brain Cell Identity
LIGER, an algorithm for integrating single-cell measurements, effectively delineates shared and dataset-specific features of brain cell identity in diverse biological contexts.
In Vitro Study
Very Rigorous JournalHighly Cited