Hedgehog signaling and cell cycle control in differentiating erythroid progenitors.

Hedgehog (Hh) signaling regulates differentiation in numerous systems, but its functions in the control of hematopoietic differentiation have not been extensively explored. Initial studies have indicated that hedgehog signaling affects the proliferation and differentiation of erythroid progenitors (Detmer, K., et al.

Clonogenic analysis reveals reserve stem cells in postnatal mammals. II. Pluripotent epiblastic-like stem cells.

Undifferentiated cells have been identified in the prenatal blastocyst, inner cell mass, and gonadal ridges of rodents and primates, including humans. After isolation these cells express molecular and immunological markers for embryonic cells, capabilities for extended self-renewal, and telomerase activity. When allowed to differentiate, embryonic stem cells express phenotypic markers for tissues of ectodermal, mesodermal, and endodermal origin.

Adult reserve stem cells and their potential for tissue engineering.

Tissue restoration is the process whereby multiple damaged cell types are replaced to restore the histoarchitecture and function to the tissue. Several theories have been proposed to explain the phenomenon of tissue restoration in amphibians and in animals belonging to higher orders. These theories include dedifferentiation of damaged tissues, transdifferentiation of lineage-committed progenitor cells, and activation of reserve precursor cells.