Differential Expression of Titin and Obscurin mRNA in Striated Muscles of the Long-Tailed Ground Squirrel Urocitellus undulatus

Seasonal changes in mRNA levels of the giant sarcomeric cytoskeletal proteins titin and obscurin were studied in the skeletal m. longissimus dorsi and the cardiac (left ventricular) muscle in the long-tailed ground squirrel Urocitellus undulatus using real-time RT-PCR. The animals were divided into the following experimental groups: “summer activity”, “fall activity”, “hypothermia” (hibernation), “winter activity” (n = 5 per group). In the cardiac muscle of “hypothermia” animals, titin mRNA levels decreased by 28% (p ≤ 0.01); in the other three groups, no statistically significant differences in this parameter were found. In m. longissimus dorsi of “hypothermia” and “winter activity” animals, titin mRNA levels increased by 2.9 (p ≤ 0.01) and 3.6 (p ≤ 0.01) times, respectively, with no statistically significant differences in this parameter in “summer activity” and “fall activity” animals. Obscurin mRNA levels increased by 3.4–3.6 times (p ≤ 0.01) in the cardiac muscle of “fall activity”, “hypothermia” and “winter activity” animals, and by 3.0 and 3.6 times (p ≤ 0.01) in the skeletal muscle of “hypothermia” and “winter activity” animals, respectively. Thus, we report here for the first time the data on the differential expression of titin and obscurin mRNAs, indicating concerted changes in the giant cytoskeletal proteins in muscles of the long-tailed ground squirrel during hibernation. The results are discussed in the context of striated muscle adaptation to hibernation in this rodent species.