The presence of desmin was characterized in cultured rat and bovine satellite cells and its potential usefulness as a marker for identifying satellite cells in vitro was evaluated. In primary cultures, positive immunohistochemical staining for desmin and skeletal muscle myosin was observed in rat and bovine myotubes. A small number of mononucleated cells (20% of rat satellite cells and 5% of bovine satellite cells) were myosin-positive, indicative of post-mitotic differentiated myocytes. In bovine satellite cell cultures 13% of the mononucleated cells were desmin-positive, while 84% of the mononucleated cells in rat satellite cell cultures were desmin-positive. Rat satellite cell mass cultures and bovine satellite cell clonal density cultures were pulsed with 3H-thymidine, and autoradiographic data revealed that greater than 94% of dividing rat cells were desmin-positive, suggesting that desmin is synthesized in proliferating rat satellite cells. However, no desmin was seen in cells that incorporated labeled thymidine in bovine satellite cell clones. Analysis of clonal density cultures revealed that only 14% of the mononucleated cells in bovine satellite cell colonies were desmin-positive, whereas 98% of the cells in rat satellite cell colonies were desmin-positive. Fibroblast colonies from both species were desmin-negative. In order to further examine the relationship between satellite cell differentiation and desmin expression, 5-bromo-2'-deoxyuridine (BrdU) was added to culture medium at the time of plating to inhibit differentiation. Fusion was inhibited in rat and bovine cultures, and cells continued to divide. Very few desmin-positive cells were found in bovine cultures, but greater than 90% of the cells in rat cultures stained positive for desmin. The presence of desmin and sarcomeric myosin was also evaluated in regenerating rat tibialis anterior five days after bupivacaine injection. In regenerating areas of the muscle many desmin-positive cells were present, and only a few cells stained positive for skeletal muscle myosin. Application of desmin staining to rat satellite cell growth assays indicated that rat satellite cells cultured in serum-containing medium were contaminated with fibroblasts at levels that ranged from approximately 5% in 24 hr cultures to 15% in mature cultures. In defined medium 4 day cultures contain approximately 95% to 98% desmin-positive satellite cells.(ABSTRACT TRUNCATED AT 400 WORDS)

This study examined the effects of basic fibroblast growth factor (bFGF), insulin-like growth factor I (IGF-I) and transforming growth factor beta (TGF-beta) on the proliferation and differentiation of primary bovine satellite cells (BSC) in vitro. Individually, these three factors had the following effects on satellite cells: bFGF stimulated proliferation (P less than .01) but inhibited differentiation (P less than .05); IGF-I had no effect on proliferation but stimulated differentiation (P less than .01); and TGF-beta inhibited both proliferation and differentiation (P less than .01). When combined, the following effects were observed: maximum stimulation of proliferation (P less than .01) occurred in the presence of bFGF and IGF-I and differentiation was not stimulated; TGF-beta and bFGF continued to inhibit differentiation (P less than .01), but in the presence of bFGF, TGF-beta stimulated proliferation (P less than .01). No stimulation was observed in the presence of TGF-beta and IGF-I. Bovine satellite cells respond to these three growth factors that have been shown to regulate the activity of other myogenic cells, and in most instances, the responses among cells from various species are similar. These experiments indicate that the interactions of growth factors may be critical in regulating bovine satellite cell activity.

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Horses competing at a high level of 3-day eventing in 2008 were at risk of reduced performance given the significant rate of gastric ulcers, decreased appetite and weight loss. Research addressing specific causes of and/or feeding management changes that would reduce the incidence of these problems in these horses is needed to ensure optimal health and performance.