The Influence of Short-term Fasting on Muscle Growth and Fiber Hypotrophy Regulated by the Rhythmic Expression of Clock Genes and Myogenic Factors in Nile Tilapia.

Circadian clock genes and myogenic factors are tightly integrated to influence muscle growth upon dietary deprivation in animals. In this study, we reported that upon short-term fasting of Nile tilapia juveniles for 7 and 15 days, the growth of the fish stagnated and the size of muscle fibers decreased. To reveal the molecular mechanisms of how starvation affects fish muscle growth, we analyzed the rhythmic expression of circadian clock genes and myogenic factors. After 7 and 15 days of fasting treatment, the muscle tissues were collected for 24 h (at zeitgeber times ZT0, ZT3, ZT6, ZT9, ZT12, ZT18, ZT21, and ZT24) from tilapia juveniles. Among the 27 clock genes, the expression of cyr1b, nr1d1, per1, clocka, clockb, ciarta, and aanat2 displayed a daily rhythmicity in normal daily cycle, while arntl2, cry1a, cry1b, npas2, nr1d2b, per2, per3, rorαb, clocka, clockb, nfil3, cipca, and cipcb exhibited daily rhythmicity in the fasting fish muscles. The transcript levels of clockb showed moderate positive correlation with the aanat2, ciarta, cry1b, and nr1d1 in the muscle tissue of normally fed Nile tilapia juvenile. In comparison of the two treatment modes, the expression levels of clocka, clockb, and cry1b showed the rhythmicity, but clockb expression was significantly decreased and the acrophase had shifted. The transcript levels of fbxo32 and pdk4 had either moderate or strong positive correlations with other daily expression of clock genes except arntl2 in the muscle after 7-day fasting. The expressions of myogenic regulatory factors were also either upregulated or downregulated. These observations demonstrated that dietary starvation might affect fish muscle growth by modulating the differential expression of circadian clock genes and myogenic factors. Thus, our work provides a better understanding of the molecular mechanism of dietary starvation on fish growth and may provide dietary administration in aquiculture.