CELL CYCLE GENE EXPRESSION DURING SKELETAL MUSCLE GROWTH

Abstract

PURPOSE Skeletal muscle growth, under some conditions, is thought to be dependent on the proliferation of satellite cells. The proliferation of satellite cells is dependent on the interaction of a number of proteins involved with the control of the cell cycle. The objective of this study was to test the hypothesis that the longitudinal growth of skeletal muscle results in the upregulation of mRNA levels of key genes responsible for promoting the cell cycle. METHODS Female Sprague-Dawley rats were assigned to the following groups: 1) control (CON; n =14); 2) frame-control; (FC; n=6); and 3) tibial osteotomy and distraction; (DIST; n = 8). Following 8 days of tibial distraction (lengthening), the soleus muscles were harvested and used for oligonucleotide microarray analyses (Affymetrix; RGU34A chipset). Analyses of the microarray data were performed using a statistical package (dCHIP) in combination with an analytical/visualization software package (GeneSpring). The results from these analyses were then integrated into a pathway for cell cycle control obtained from the Kyoto Encyclopedia of Genes and Genomes (www.kegg.com). RESULTS Approximately 30 different genes associated with the cell cycle were examined. Interestingly, the mRNA levels that were upregulated the most belonged to genes (GADD45, p21, PCNA, rb) that promote cell cycle arrest. Supplemental analyses of GADD45 (growth arrest and DNA destruction) isoforms (alpha, beta, and gamma) via RTPCR revealed significant increases (P < 0.05) in the alpha and beta isoforms. CONCLUSION The findings of this study are paradoxical to the satellite cell hypothesis, which states that skeletal muscle growth is associated with proliferation of satellite cells. It may be that the changes observed in the mRNA levels in the current study are not reflective of the protein-protein interactions involved in the regulation of cell cycle control. Funded by NIH AR46856 (VJC), AR44743 (VJC), AR45594 (GRA), and AR30346 (KMB)