Originally published as Genetics Published Articles Ahead of Print on September 9, 2008.

Genetics, Vol. 180, 821-834, October 2008, Copyright © 2008
doi:10.1534/genetics.108.093690

A Computational Approach to the Functional Clustering of Periodic Gene-Expression Profiles

* Department of Statistics, University of Florida, Gainesville, Florida 32611, {dagger} Department of Quantitative Health Sciences, Cleveland Clinic Foundation, Cleveland, Ohio 44195 and {ddagger} Department of Operation Research and Financial Engineering, Princeton University, Princeton, New Jersey 08544

2 Corresponding author: Department of Statistics, University of Florida, Gainesville, FL 32611.
E-mail: rwu{at}stat.ufl.edu

DNA microarray analysis has emerged as a leading technology to enhance our understanding of gene regulation and function in cellular mechanism controls on a genomic scale. This technology has advanced to unravel the genetic machinery of biological rhythms by collecting massive gene-expression data in a time course. Here, we present a statistical model for clustering periodic patterns of gene expression in terms of different transcriptional profiles. The model incorporates biologically meaningful Fourier series approximations of gene periodic expression into a mixture-model-based likelihood function, thus producing results that are likely to be closer to biological relevance, as compared to those from existing models. Also because the structures of the time-dependent means and covariance matrix are modeled, the new approach displays increased statistical power and precision of parameter estimation. The approach was used to reanalyze a real example with 800 periodically expressed transcriptional genes in yeast, leading to the identification of 13 distinct patterns of gene-expression cycles. The model proposed can be useful for characterizing the complex biological effects of gene expression and generate testable hypotheses about the workings of developmental systems in a more precise quantitative way.