Submitted to: Joint Abstracts of the American Dairy Science and Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: February 8, 2006
Publication Date: July 9, 2006
Citation: Gressley, T., Connor, E.E., Dahl, G.E. 2006. Liver expression of the clock gene TIMELESS is reduced by long day photoperiod in dairy steers [abstract]. J. Dairy Sci. 89(Suppl1):289.
Regulation of circadian rhythms in the brain and peripheral organs occurs via differential expression of clock genes in response to external stimuli including light and feeding time. An experiment was conducted to determine whether expression of five clock genes in the liver of steers is affected by photoperiod manipulation. Eight Holstein steers averaging 100 d of age were exposed to 12 h of light and 12 h of darkness (12L:12D) for a 14-d acclimation period. Following acclimation, steers were assigned to a crossover design with a long day photoperiod (LDPP) or a short day photoperiod (SDPP) for 9 weeks followed by the opposite treatment for 4 weeks. Light cycles were 16L:8D for LDPP and 8L:16D for SDPP, with lights on at 0800h for both treatments. Steers were fed a grain and alfalfa cube mix at 1000h daily and had free access to water. Liver biopsies were taken beginning at 0830h during week 1 of the acclimation period and on week 4 of each treatment period. Liver samples were analyzed by quantitative real-time RT-PCR for mRNA expression of five clock genes (BMAL1, CLOCK, Per1, Per2, and TIMELESS) and three housekeeping genes (RPS18, GAPDH, and ACTB). Fold difference in clock gene expression between each treatment period and the acclimation period was calculated after normalizing to the three housekeeping genes and correcting for PCR efficiency. Results indicated expression levels of BMAL1, CLOCK, Per1, and Per2 in LDPP were 99%, 97%, 101%, and 112%, respectively, of SDPP levels, with no significant differences between treatments. However, expression of TIMELESS for LDPP was reduced to 73% of SDPP (P = 0.08). The TIMELESS protein is involved in regulating circadian rhythms and has recently been implicated in coupling the cell division cycle to circadian rhythms. Photoperiod manipulation appears to entrain the circadian rhythm of clock gene expression in the bovine liver and may consequently affect liver metabolism.