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Japanese Wagyu cattle are well known for their extremely high marbling, with poorly defined mechanisms.The objective is to evaluate breed differences in the structure of subcutaneous (SQ) fat tissue, adipogenesis and mitogenesis of stromal vascular (SV) cells between Wagyu and Angus cattle.Histologic analysis of fat tissue indicated Wagyu had larger adipocytes and more abundant small cells compared to Angus cattle.At the tissue level, the protein expression of PPARγ in Wagyu was much lower compared to Angus (P < 0.001).Similarly, the lower mRNA expression of PPARγ was found in Wagyu SV cells (P < 0.05).As assessed by oil red-O staining, Wagyu SV cells possessed a notable trend of lower adipogenic ability (P =0.094).Interestingly, significant higher mitogenic ability was discovered in Wagyu SV cells (P =0.028), which was associated with the elevated phosphorylation of extracellular signal-regulated kinase (Erk)-1/2 (P =0.013).Moreover, exogenous fibroblast growth factor (FGF)-2 enhanced mitogenesis and Erk1/2 activity of SV cells to a greater degree in Angus compared to Wagyu (Angus: 176.42 ± 29.17% for mitogenesis and 210.00 ± 100.45% for Erk1/2 phosphorylation, P < 0.001 and P =0.003; Wagyu: 71.86 ± 31.11% for mitogenesis and 42.64 ± 33.51% for Erk1/2 phosphorylation, P =0.065 and P =0.033).Comparisons of mRNA expressions for several autocrine growth factors in Wagyu and Angus cattle showed the expression of transforming growth factor (TGF)-β3 (P =0.008) and bone morphogenetic protein (BMP)-2 (P =0.043) in Wagyu SV cells was lower than that of Angus cattle.Because both TGFβ3 and BMP2 are transforming growth factors known to inhibit proliferation, their lower expression in Wagyu might provide clues for breed differences on proliferation of SV cells in these two cattle breeds.