A. J. Friedenstein, J. F. Gorskaja and N. N. Kulagina, “Fibroblast Precursors in Normal and Irradiated Mouse Hematopoietic Organs,” Experimental Hematology, Vol. 4, No. 5, 1976, pp. 267-274.
 D. J. Prockop, “Marrow Stromal Cells as Stem Cells for Nonhematopoietic Tissues,” Science, Vol. 4, No. 276, 1997, pp. 71-74.
 M. F. Pittenger, A. M. Mackay, S. C. Beck, R. K. Jaiswal, R. Douglas, J. D. Mosca, M. A. Moorman, D. W. Simonetti, S. Craig and D. R. Marshak, “Multilineage Potential of Adult Human Mesenchymal Stem Cells,” Science, Vol. 284, No. 5411, 1999, pp. 143-147.
 C. E. Sarraf, W. R. Otto and M. Eastwood, “In Vitro Mesenchymal Stem Cell Differentiation after Mechanical Stimulation,” Cell Proliferation, Vol. 44, No. 1, 2011, pp. 99-108.
 V. Lettry, K. Hosoya, S. Takagi and M. Okumura, “Co-culture of Equine Mesenchymal Stem Cells and Mature Equine Articular Chondrocytes Results in Improved Chondrogenic Differentiation of the Stem Cells,” Japanese Journal of Veterinary Research, Vol. 58, No. 1, 2010, pp. 5-15.
 J. Koerner, D. Nesic, J. D. Romero, W. Brehm, P. Mainil-Varlet and S. P. Grogan, “Equine Peripheral Blood- Derived Progenitors in Comparison to Bone Marrow-Derived Mesenchymal Stem Cells,” Stem Cells, Vol. 24, No. 6, 2006, pp. 1613-1619.
 F. Barry and J. Murphy, “Mesenchymal Stem Cells: Clinical Applications and Biological Characterization,” The International Journal of Biochemistry & Cell Biology, Vol. 36, No. 4, 2004, pp. 568-584.
 H. Castro-Malaspina, R. E. Gay, G. Resnick, N. Kapoor, P. Meyers, D. Chiarieri, S. McKenzie, H. E. Broxmeyer and M. A. Moore, “Characterization of Human Bone Marrow Fibroblast Colony-Forming Cells (CFU-F) and Their Progeny,” Blood, Vol. 56, No. 2, 1980, pp. 289- 301.
 E. Karaoz, A. Aksoy, S. Ayhan, A. E. Sariboyaci, F. Kaymaz and M. Kasap, “Characterization of Mesenchymal Stem Cells from Rat Bone Marrow: Ultrastructural Properties, Differentiation Potential and Immunophenotypic Markers,” Histochemistry and Cell Biology, Vol. 132, No. 5, 2009, pp. 533-546.
 S. Raimondo, C. Penna, P. Pagliaro and S. Geuna, “Morphological Characterization of GFP Stably Transfected Adult Mesenchymal Bone Marrow Stem Cells,” Journal of Anatomy, Vol. 208, No. 1, 2006, pp. 3-12.
 I. Sekiya, D. C. Colter and D. J. Prockop, “BMP-6 Enhances Chondrogenesis in a Subpopulation of Human Marrow Stromal Cells,” Biochemical and Biophysical Research Communications, Vol. 284, No. 2, 2001, pp. 411-418. http://dx.doi.org/10.1006/bbrc.2001.4898
 G. Pasquinelli, P. Tazzari, F. Ricci, C. Vaselli, M. Buzzi, R. Conte, C. Orrico, L. Foroni, A. Stella, F. Alviano, G. P. Bagnara and E. Lucarelli, “Ultrastructural Characteristics of Human Mesenchymal Stromal (Stem) Cells Derived From Bone Marrow and Term Placenta,” Ultrastructural Pathology, Vol. 31, No. 1, 2007, pp. 23-31.
 G. Teti, C. Cavallo, B. Grigolo, S. Giannini, A. Facchini, A. Mazzotti and M. Falconi, “Ultrastructural Analysis of Human Bone Marrow Mesenchymal Stem Cells during in Vitro Osteogenesis and Chondrogenesis,” Microscopy Research and Technique, Vol. 75, No. 5, 2012, pp. 596-604.
 C. Csaki, U. Matis, A. Mobasheri, H. Ye and M. Shakibaei, “Chondrogenesis, Osteogenesis and Adipogenesis of Canine Mesenchymal Stem Cells: A Biochemical, Morphological and Ultrastructural Study,” Histochemistry and Cell Biology, Vol. 128, No. 6, 2007, pp. 507-520.