| Meiosis is a specialized form of cell division necessary for sexual reproduction in eukaryotes. I was interested in understanding the molecular basis for the difference between meiosis and mitosis in budding yeast. I began by characterizing a gene, NDT80, expressed only during sporulation (the combined processes of meiosis and spore formation) which is necessary for progression from meitoic prophase into the first meiotic division (Xu et al., 1995). I found that Ndt80 is a transcription factor responsible for activating expression of many genes during sporulation, including most of the B-type cyclins, the regulatory subunits of the Cdc28/cyclin complex. In addition, Ndt80 activity appears to be under checkpoint control, being dependent on successful completion of meiotic recombination. These and other observations support the hypothesis that sporulation is regulated by a transcriptional cascade. To pursue this line of study further, I embarked on a comprehensive analysis of gene expression during sporulation at the whole genome level in collaboration with Joe DeRisi and others at Stanford University. Nearly one-tenth of the yeast genome is induced during sporulation. Ndt80 is responsible for transcription of the largest of seven classes of genes induced during sporulation. Using microarray analysis as an unbiased genetic screen, we characterized three novel genes induced with different kinetics during sporulation and found each to be essential for sporulation. We hope that this and additional studies based on the sporulation expression data will bring us one step closer to understanding how meiosis is a specialized form of the cell cycle. |
