Abstract: [Objective] By comparing the differences of proliferation rate, surface marker molecules, pluripotent gene expression and cartilage differentiation potential of umbilical cord mesenchymal stem cells (UC-MSCs) isolated from three different parts of the same umbilical cord of female equine fetus, the umbilical cord site which was suitable for isolation and culture of mesenchymal stem cells (MSCs) was identified. [Method] MSCs were isolated from the umbilical cord near the fetus (proximal end), the center of the umbilical cord (middle segment) and the placenta (distal end), and the proliferation ability of UC-MSCs was compared by plotting cell growth curve, the expression of multipotent genes and surface marker molecules were detected by Real-time quantitative PCR, and the potential of cartilage differentiation was detected by cartilage induction. [Result] The MSCs isolated from the proximal end, middle segment, and distal end attached to the wall and grew in a fibrous shape and the doubling time were 35.4, 25.5 and 34.9 h, respectively, and all of them expressed NANOG homeobox (NANOG), POU class 5 homebox 1 (POU5F1) and SRY-box transcription factor 2 (SOX2), overexpression of 5'-nucleotidase ecto (CD73), Thy-1 cell surface antigen (CD90), endoglin (CD105) and hematopoietic progenitor cell antigen (CD34), low expression of CD14 molecule (CD14), B-lymphocyte surface antigen B4 (CD19), protein tyrosine phosphatase receptor type C (CD45) and B cell antigen receptor complex associated protein α chain (CD79a). The relative expression of pluripotent gene NANOG in middle segment P1 cells was significantly higher than that in proximal end P1 cells (P<0.05), the relative expression of POU5F1 in P5 proximal end cells was significantly higher than that in middle segment cells (P<0.05), and it was extemely significantly higher than that of distal end cells (P<0.01). The relative expressions of CD14, CD19, CD73 and CD90 in P5 proximal end cells were significantly or extemely significantly higher than those in middle segment and distal end cells (P<0.05; P<0.01), the relative expressions of CD34 and CD79a in distal end cells of P5 generation was significantly or very significantly higher than that in proximal end and middle segment cells (P<0.05; P<0.01). The UC-MSCs derived from the proximal end, middle segment and distal end could be induced to differentiate into chondrocytes. On the 14th day of induced differentiation, the relative expression of SOX9 in proximal cells was extremely significantly higher than that in distal cells (P<0.05), and on the 21st day of induction, the relative expression of SOX9 in distal cells was extremely significantly higher than that in middle cells (P<0.01). The relative expressions of specific gene aggrecan (ACAN) and collagen type Ⅱ alpha 1 chain (COL2A1) in middle segment cells were extremely significantly higher than those in proximal and distal cells on the 7th and 14th day of induction (P<0.01), and significantly higher than those in proximal and distal cells on the 21st day (P<0.05). [Conclusion] The proximal end, middle segment and distal end of umbilical cord could be used to prepare MSCs, which could express pluripotent genes and MSCs surface marker molecules, and could be induced to differentiate into chondrocytes. The proliferation ability and cartilage differentiation potential of MSCs from the middle segment were better than those from the proximal and distal ends, so they were more suitable for isolating MSCs.

Key words: equine; umbilical cord mesenchymal stem cells (UC-MSCs); pluripotency; surface marker molecule; chondrogenic differentiation