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Minerva Biotecnologica 2005 June;17(2):55-63

Copyright © 2005 EDIZIONI MINERVA MEDICA

language: English

Adult-derived stem cells

Young H. E. ^{1, 2}, Black A. C. Jr. ^{1, 3}

¹ Division of Basic Medical Sciences, Mercer University School of Medicine, Macon, GA, USA; ² Department of Pediatrics, Mercer University School of Medicine, Macon, GA, USA; ³ Department of Obstetrics and Gynecology, Mercer University School of Medicine, Macon, GA, USA

Four categories of cells have been previously identified in postnatal mammals, including humans. These categories are differentiated cells, cell- and tissue-committed progenitor cells, germ layer lineage-committed stem cells and lineage-uncommitted pluripotent stem cells. All 4 categories of cells display normal karyotypes. Differentiated cells are variable in size. They form the physiological functional components of the tissue. Progenitor cells are also variable in size and are the immediate precursors of differentiated cells. Germ layer lineage stem cells range in size from 10-20 µm and can be induced to form multiple cell types belonging to their respective ectodermal, mesodermal, and endodermal embryological lineages. Pluripotent stem cells range in size from 6-8 µm and will form somatic cell types from all 3 primary germ layer lineages, but will not form the sperm or ova. Differentiated cells, progenitor cells, and germ layer lineage stem cells are contact inhibited at confluence. In contrast, pluripotent stem cells can form multiple layers of cells post confluence. Differentiated cells and progenitor cells demonstrate a finite life span before replicative senescence and cell death occur. Both germ layer lineage stem cells and pluripotent stem cells are telomerase positive and display extensive capabilities for self-renewal. Recently, a 5th category of cell was discovered in postnatal tissues. These putative stem cells are less than 1 µm in size. They demonstrate a normal karyotype. These cells are the immediate precursors to the pluripotent stem cells. They can form all somatic cells of the body and spermatogonia. These cells have shown extensive capabilities for self-renewal. They will form multiple layers of cells post confluence. Shared and unique characteristics will be discussed for these 5 categories of adult-derived cells.