The Drosophila dCREB2 gene affects the circadian clock

Abstract

We report the role of dCREB2, the Drosophila homolog of CREB/CREM, in circadian rhythms. dCREB2 activity cycles with a 24 hr rhythm in flies, both in a light:dark cycle and in constant darkness. A mutation in dCREB2 shortens circadian locomotor rhythm in flies and dampens the oscillation of period, a known clock gene. Cycling dCREB2 activity is abolished in a period mutant, indicating that dCREB2 and Period affect each other and suggesting that the two genes participate in the same regulatory feedback loop. We propose that dCREB2 supports cycling of the Period/Timeless oscillator. These findings support CREB's role in mediating adaptive behavioral responses to a variey of environmental stimuli (stress, growth factors, drug addiction, circadian rhythms, and memory formation) in mammals and long-term memory formation and circadian rhythms in Drosophila.

Figure 1.

Cycling of a dCREB2-Responsive Reporter (A) Constructs used to generate CRE–luc and mCRE–luc transgenic flies. Abbreviations: P, P transposable element inverted repeats; INS, SCS and SCS′ insulator elements; TATA, TATA box sequence from hsp 70 promoter. These constructs were cloned into the pCaSpeR transformation vector. (B) In vivo cycling of CRE–luc and mCRE–luc reporter expression as measured in a Packard TopCount Luminometer (see Experimental Procedures). All time points represent an average of data points from 30 flies. The bar below the graph indicates light:dark conditions. White box, light period; black box, dark period; gray box, dark period during former light hours (subjective day). Vertical bars in the graph represent lights out and are spaced 24 hr apart. (C) Similar graph as in (B) but with standard error bars added.

Figure 2.

Characterization of the S162 Mutation (A) Crossing S162/FM7 heterozygous females to wild-type males results in fewer than 0.5% of the male progeny carrying the S162 mutation (left panel). This percentage of S162 males can be increased by crossing S162/FM7 females to transgenic males homozygous for a heat shock–inducible form of dCREB2, hs-dCREB2–10. This construct encodes an isoform of dCREB2 (see Experimental Procedures). The transgene is induced by a daily 60 min heat shock of 37°C during the larval and pupal stages of development. This results in 50% of the male progeny carrying the S162 mutation (right panel). (B) Western blot analysis of extracts from wild-type males and S162 escaper males. Extracts were prepared from whole flies and were analyzed on a 12% denaturing SDS–polyacrylamide gel followed by Western blot analysis. A mouse monoclonal antibody (mAb 27) raised against full-length dCREB2 was used to probe the membrane. This antibody recognizes two wild-type dCREB2 proteins of about 38–40 kDa, indicated by the arrow. The S162 mutant forms are indicated by an arrowhead. The high molecular weight band observed in both lanes is a cross-reacting band. (C) Expression of the CRE–luc reporter in S162 mutant flies. S162/FM7 females were mated to males homozygous for the CRE–luc reporter transgene. Escaper males of the genotype S162/Y; CRE–luc/+ were assayed in the luminometer. The traces represent an average of data from 15 flies (S162 mutants) or 30 flies (wild type). See Figure 1 legend for description of the graph.

Figure 3.

dCREB2 Protein Levels Do Not Appear to Cycle in a Circadian Rhythm Western blot analysis of extracts prepared from adult fly heads. Flies were collected every 4 hr over a 24 hr period. Total extracts were prepared from heads, and equal amounts of protein were loaded and analyzed by Western blot as described in Figure 2.

Figure 4.

Circadian Locomotor Activity Defect of S162 Mutant Flies and Rescue by hs-dCREB2–10 Flies were analyzed for circadian locomotor activity as described in the Experimental Procedures. Both S162 mutant flies (black bars) and S162 mutants that had been rescued by developmental induction of hs-dCREB2–10 (gray bars) were assayed. See also Table 1.

Figure 5.

Expression of per–luc and BG–luc Reporters in the S162 Mutant Background (A) Expression of the per–luc reporter in a wild-type or S162 mutant background. For the wild-type background, +/+ females were crossed to per–luc homozygous males, and per–luc/+ male progeny were tested. For the S162 background, S162/FM7 females were crossed to homozygous per–luc males, and escaper males of the genotype S162/Y; per–luc/+ were tested. Crosses were similar for experiments with BG–luc. (B) Expression of the BG–luc reporter in a wild-type or S162 mutant background. (C) Replotting of the first 48 hr of the graph in (B). The solid lines are placed at the peaks of the wild-type curve, and the dashed lines are at the peaks of the S162 curve.

Figure 6.

Per Protein Expression in Wild-Type and S162 Mutant Flies (A) Head extracts from wild-type flies were analyzed by Western blot using a Per antibody. Flies were collected every 2 hr throughout the circadian cycle and are plotted from ZT 0 (far left lane) to ZT 22 (far right lane). Per protein is present as a series of bands indicated by the arrow. (B) Head extracts from S162 flies analyzed as in panel (A). (C and D) Same blots as in (A) and (B) but probed with an antibody to Tim protein.

Figure 7.

Expression of the CRE–luc Reporter in per Mutant Backgrounds Females homozygous for one of three per mutations (described in the text) were crossed to males homozygous for the CRE–luc reporter, and male progeny of the genotype per/Y; CRE–luc/+ were assayed in the luminometer. Abbreviations: pero, per⁰ or per null; perl, per^l or per long; pers, per^s or per short. The flies had been entrained to a 12 hr light:12 hr dark cycle for 4 days before the start of the experiment. The flies were then switched to constant darkness for the duration of the experiment. Each trace represents the average of data from 40 flies.