Comparison of clock gene expression across skeletal muscles of different origins and functions

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Circadian rhythms are approximate 24 hour cycles and are associated with many physiological processes in the body. The molecular clock mechanism that underlies circadian rhythms has been found to exist in all cells in both central and peripheral tissues. Our lab has demonstrated that clock genes oscillate in gastrocnemius muscle but nothing is known about clock gene expression in muscles that have different developmental origins and different functions. In this study we compared clock gene expression in gastrocnemius, tongue and diaphragm muscles that were collected from mice every 4 hr for 28 hr. RNA was isolated from each tissue and real time polymerase chain reaction (PCR) was performed to determine mRNA levels of select clock and clock‐controlled genes. The results indicate that core clock genes, Bmal1 and Per2, oscillate with a similar phase across all three muscles. However we found that other clock genes, including Per1 and Cry2 oscillated in gastrocnemius and diaphragm but not tongue. Previously characterized clock controlled genes, MyoD and PGC1 á were found not to oscillate in either diaphragm or tongue. These findings confirm that some core clock genes are oscillating in diverse skeletal muscle but identified that not all components of the clock are conserved.Support for this work is from NIH R01AR055246 to KAE.