title: Implications of Epigenetic Variability within a Cell Population for "Cell Type" Classification.
abstract: Here, we propose a new approach to defining nerve "cell types" in reaction to recent advances in single cell analysis. Among cells previously thought to be equivalent, considerable differences in global gene expression and biased tendencies among differing developmental fates have been demonstrated within multiple lineages. The model of classifying cells into distinct types thus has to be revised to account for this intrinsic variability. A "cell type" could be a group of cells that possess similar, but not necessarily identical properties, variable within a spectrum of epigenetic adjustments that permit its developmental path toward a specific function to be achieved. Thus, the definition of a cell type is becoming more similar to the definition of a species: sharing essential properties with other members of its group, but permitting a certain amount of deviation in aspects that do not seriously impact function. This approach accommodates, even embraces the spectrum of natural variation found in various cell populations and consequently avoids the fallacy of false equivalence. For example, developing neurons will react to their microenvironments with epigenetic changes resulting in slight changes in gene expression and morphology. Addressing the new questions implied here will have significant implications for developmental neurobiology.
authors.affiliation: Laboratory of Neurobiology and Behavior, The Rockefeller University New York, NY, USA.
authors.forename: Inna
authors.initials: I
authors.lastname: Tabansky
authors.affiliation: Laboratory of Neurobiology and Behavior, The Rockefeller UniversityNew York, NY, USA; Departments of Neurology and Science Education, Hofstra North Shore-LIJ School of MedicineHempstead, NY, USA; Department of Autoimmunity, The Feinstein Institute for Medical Research, North Shore-LIJ Health SystemManhasset, NY, USA.
authors.forename: Joel N H
authors.initials: JN
authors.lastname: Stern
authors.affiliation: Laboratory of Neurobiology and Behavior, The Rockefeller University New York, NY, USA.
authors.forename: Donald W
authors.initials: DW
authors.lastname: Pfaff
keywords: cell type classification; functional equivalence; in vitro culture; single cell analysis; variability in gene expression