¹Stem Cell Biology Program at James Graham Brown Cancer Center, University of Louisville, Louisville, KY, USA

Correspondence: Professor MZ Ratajczak, Stem Cell Biology Program, James Graham Brown Cancer Center, University of Louisville, Louisville, KY 40202, USA. E-mail: mzrata01@louisville.edu

Received 29 January 2006; Accepted 10 February 2006; Published online 23 February 2006.

Abstract

By employing multiparameter sorting, we identified in murine bone marrow (BM) a homogenous population of rare (0.02% of BMMNC) Sca-1⁺lin^-CD45^- cells that express by RQ-PCR and immunohistochemistry markers of pluripotent stem cells (PSC) such as SSEA-1, Oct-4, Nanog and Rex-1. The direct electronmicroscopical analysis revealed that these cells are small (2–4 m), posses large nuclei surrounded by a narrow rim of cytoplasm, and contain open-type chromatin (euchromatin) that is typical for embryonic stem cells. In vitro cultures these cells are able to differentiate into all three germ-layer lineages. The number of these cells is highest in BM from young (1-month-old) mice and decreases with age. It is also significantly diminished in short living DBA/2J mice as compared to long living B6 animals. These cells in vitro respond strongly to SDF-1, HGF/SF and LIF and express CXCR4, c-met and LIF-R, respectively, and since they adhere to fibroblasts they may be coisolated with BM adherent cells. We hypothesize that this population of Sca-1⁺lin^-CD45^- very small embryonic-like (VSEL) stem cells is deposited early during development in BM and could be a source of pluripotent stem cells for tissue/organ regeneration.