title: Stem cells: shibboleths of development, part II: Toward a functional definition.
abstract: Our previous discourse on stem cell characteristics led to the conclusion that the qualities deemed essential for a cell to be considered a "stem cell" are neither firmly established nor universally accepted, and this we accept as editorial policy. In that study, self-renewal, asymmetric division, phenotypic markers, and other attributes touted as being indicative of cells being stem cells were critically questioned as fundamental to the definition of a stem cell, leading us to seek a functional definition instead. Here, we offer further considerations, and elaborate on the characteristics that diverse investigators feel are essential for a cell to function as a stem cell, either in development or body maintenance. We hope that this discourse will promote further reflection, culminating with a definition that is widely accepted and universally applicable. We confess this goal has not been reached, neither here nor elsewhere. The outstanding goal of understanding what stem cells are, a prerequisite of characterizing what stem cells do and how they do it, is still outstanding.
authors.affiliation: Children's Research Center of Michigan, the Carman and Ann Adams Department of Pediatrics, Wayne State University School of Medicine, Detroit, MI 48201, USA.
authors.forename: Graham C
authors.initials: GC
authors.lastname: Parker
authors.forename: Marlene
authors.initials: M
authors.lastname: Anastassova-Kristeva
authors.forename: Leonard M
authors.initials: LM
authors.lastname: Eisenberg
authors.forename: Mahendra S
authors.initials: MS
authors.lastname: Rao
authors.forename: Marc A
authors.initials: MA
authors.lastname: Williams
authors.forename: Paul R
authors.initials: PR
authors.lastname: Sanberg
authors.forename: Denis
authors.initials: D
authors.lastname: English
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D006801:Humans; D013234:Stem Cells / Q000145:classification / Q000166:cytology / Q000502:physiology