Global profiling of the circadian transcriptome using microarrays.

Circadian rhythms are biological cycles with a period length of approximately 24 h that are generated by endogenous clocks. The application of microarrays for high-throughput transcriptome analysis has led to the insight that substantial portions of the transcriptomes of both humans and many model organisms are clock-regulated. In a typical circadian time course microarray experiment, samples are collected from organisms maintained in constant environmental conditions, gene expression at each time point is determined using microarrays, and finally clock-regulated transcripts are identified using statistical algorithms. Here, we describe how to design the experiment, process RNA, determine expression profiles using ATH1 microarrays, and use a nonparametric statistical algorithm named JTK_CYCLE in order to identify circadian-regulated transcripts in Arabidopsis. This basic procedure can be modified to identify clock-regulated transcripts in different organisms or using different expression analysis platforms.