Statistical Analysis
Data were analyzed using the general linear model procedure of Statistical Analysis Systems (SAS Institute, 1995) to determine differences within the control and LSN lines at each sampling interval. Differences between means were determined using Student's t-test. Differences were considered significant if P < 0.05.
Results and Discussion
Expression levels of the β1 integrin subunit were compared in control and LSN satellite cell cultures. Satellite cell cultures offer the advantage of being able to induce differentiation by changing the culture medium (Blaschuk and Holland, 1994). Therefore, β1 integrin expression can be examined separately during proliferation and differentiation. During the 96 hours of proliferation, β1 integrin levels did not differ between control and LSN satellite cells (Figure 1). After inducing differentiation, β1 integrin expression rapidly increased during the first 24 hours of differentiation and then declined. The β1 integrin expression levels increased after 36 hours of differentiation but never exhibited amounts measured at 24 hours. Throughout differentiation, LSN β1 integrin expression was significantly lower than that measured for control satellite cell cultures.
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| Figure 1: The b1 integrin expression during normal and Low Score Normal (LSN) satellite cell proliferation and differentiation. Sampling times during proliferation are indicated on the X-axis with a P and differentiation with a D. *Indicates a significant difference (P < 0.05) between control and LSN satellite cells at each sampling interval. Error bars represent the standard deviation. OD = optical density. |
Integrin expression is associated with adhesion of the cell to the extracellular matrix and cell migration (Boettiger et al., 1995; Chon et al., 1998). Early in differentiation, cell migration is occurring at a high rate resulting in the formation of multinucleated myotubes. It is likely that initial differentiation requires a high expression of integrins to adhere cells to the matrix substrate, permit cellular migration, and initiate the differentiation process. The down modulation of the β1 integrin subunit during later stages of differentiation suggests a decreased requirement for a high affinity interaction with the matrix during the transition to multinucleated myotubes. How the decreased amounts of LSN β1 integrin during differentiation affects sarcomere assembly and cytoskeletal structure is the subject of ongoing studies.