Gene expression profiling of HeLa cells in G1 or G2 phases.

The cell division cycle is regulated through both transcriptional and post-transcriptional mechanisms. The altered expression of a number of genes at the mRNA level is known to be essential for progression through the cell cycle, however, a comprehensive gene expression profile of human cells remains to be completed. Here we sought to monitor the differential gene expression of genes after the transition of G2 cells into G1 prior to the restriction point. GeneChip containing microarrays of oligonucleotides corresponding to over 12 000 human genes were employed to profile differential gene expression in G1 and G2. After three independent experiments the resultant data was filtered and a set of genes was compiled based on at least threefold-altered expression, no background noise in determining expression and observation in all experiments. Our analysis identified 154 genes that were elevated in G2 phase of cells as compared to early G1 phase including 15 novel genes. This number included mRNAs whose upregulation is known to occur in G2 phase. Surprisingly only 19 genes were upregulated in G1 phase, among these six genes were novel. Some of these genes are candidates for transition through early G1. This gene inventory for G1 and G2 phases of cell cycle will provide the basis for understanding of cell cycle delay as a result of DNA damage.