Bone marrow-derived very small embryonic-like stem cells: their developmental origin and biological significance.

Data from our and other laboratories provide evidence that bone marrow (BM) contains a population of stem cells that expresses early developmental markers such as (1) stage-specific embryonic antigen (SSEA) and (2) transcription factors Oct-4 and Nanog. These are the markers characteristic for embryonic stem cells, epiblast stem cells, and primordial germ cells (PGC). The presence of these stem cells in adult BM supports the concept that this organ contains some population of pluripotent stem cells that is deposited in embryogenesis during early gastrulation. We hypothesize that these cells could be direct descendants of the germ lineage that, to pass genes on to the next generations, has to create soma and, thus, becomes a "mother lineage" for all somatic cell lineages present in the adult body. Germ potential is established after conception in totipotent zygotes and retained in blastomeres of morula, cells from the inner cell mass of blastocyst, epiblast, and population of PGC. We will present a concept that SSEA(+) Oct-4(+) Nanog(+) cells identified in BM could be descendants of epiblast cells as well as some rare migrating astray PGC. 2007 Wiley-Liss, Inc