Previous studies have noted the presence of mesenchymal stem cells located within the connective tissue matrices of avian skeletal muscle, dermis, and heart. In these studies, clonal analysis coupled with dexamethasone treatment revealed the presence of multiple populations of stem cells composed of both lineagecommitted progenitor mesenchymal stem cells and lineage-uncommitted pluripotent mesenchyma1 stem cells. The present study was undertaken to assess the distribution of these stem cells in the connective tissues throughout various regions of the body. Day 11 chick embryos were divided into 26 separate regions. Heart, limb skeletal muscle, and limb dermis were included as control tissues. Cells were harvested enzymatically and grown using conditions optimal for the isolation, cryopreservation, and propagation of avian mesenchymal stem cells. Cell aliquots were plated, incubated with various concentrations of dexamethasone, and examined for differentiated phenotypes. Four recurring phenotypes appeared in dexamethasone-treated stem cells: skeletal muscle myotubes, fat cells, cartilage nodules, and bone nodules. These results suggest that progenitor mesenchymal stem cells and putative pluripotent mesenchymal stem cells with the potential to form at least four tissues of mesodermal origin have a widespread distribution throughout the body, being located within the connective tissue compartments of many organs and organ systems.

Progenitor and pluripotent stem cells reside within connective tissue compartments. They are also present in granulation tissue. This study examined the effects of treating these two cell populations with eight bioactive factors. Cells were assayed for DNA content as a measure of proliferation and for tissue-specific phenotypic markers as measures of lineage progression and lineage commitment. Platelet-derived endothelial growth factor and insulin-like growth factor-II did not induce proliferation in either population. However, dexamethasone, insulin, insulin-like growth factor-I, muscle morphogenetic protein, platelet-derived growth factor-AA, and platelet-derived growth factor-BB stimulated proliferation in one or both cell populations. Platelet-derived growth factor-BB was the most potent stimulator of proliferation in either population. Phenotypic expression markers were induced in the progenitor cells by insulin, insulin-like growth factor-I, insulin-like growth factor-II, dexamethasone, and muscle morphogenetic protein. However, only dexamethasone and muscle morphogenetic protein induced phenotypic expression markers in the pluripotent cells. Platelet-derived endothelial cell growth factor, platelet-derived growth factor-AA, and platelet-derived growth factor-BB did not induce phenotypic expression markers in progenitor or pluripotent cells. This study suggests the potential for using progenitor and pluripotent cells as an in vitro model to ascertain the effects of various bioactive factors on stem cells potentially involved in tissue maintenance and repair.

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