G.2 Terminology relating to developmental potential
Pluripotent: The state of a single cell that is capable of differentiating into all tissues of an organism, with exception of the extraembryonic cell types.
Multipotent: The state of single cells that are capable of differentiating into multiple cell types, but not all of the cells of an organism. Multipotent cells, exemplified by the hematopoietic stem cell, give rise to a range of cells within a specific tissue. Within the developing organism multipotent cells may give rise to derivatives of more than one embryonic germ layer, as for mesendodermal progenitors. In the adult, multipotent cells are typically restricted to becoming derivatives of a specific germ layer (endoderm, ectoderm, mesoderm), organ, or tissue.
Teratoma: A benign, encapsulated mass of complex differentiated tissues comprising elements of all three embryonic germ layers: ectoderm, endoderm, and mesoderm. In the context of stem cell research, the teratoma assay entails injection of cell populations into immune-deficient murine hosts to assess their pluripotency (their capacity to produce derivatives from all three germ layers). These structures are distinct from teratocarcinomas in which, in addition to the differentiated derivatives, undifferentiated stem cells persist.
Totipotent: The state of a cell that is capable of giving rise to all types of differentiated cells found in an organism, as well as the supporting extra-embryonic structures of the placenta. A single totipotent cell might, by division in utero, reproduce the whole organism, but to date this has only been demonstrated by zygotes or blastomeres of early cleavage stage embryos.
Unipotent: The state of single cells that are capable of differentiating only along a specific cell lineage and are exemplified by lineage-committed progenitors of the hematopoietic system (for example, erythroblasts). Unipotent stem cells undergo self-renewal and differentiation along a single lineage, as exemplified by the spermatogonial stem cell.