Global mRNA expression analysis in myosin II deficient strains of Saccharomyces cerevisiae reveals an impairment of cell integrity functions

Background: The Saccharomyces cerevisiae MYO1 gene encodes the myosin II heavy chain (Myo1p), a protein required for normal cytokinesis in budding yeast. Myo1p deficiency in yeast (myo1 Delta) causes a cell separation defect characterized by the formation of attached cells, yet it also causes abnormal budding patterns, formation of enlarged and elongated cells, increased osmotic sensitivity, delocalized chitin deposition, increased chitin synthesis, and hypersensitivity to the chitin synthase III inhibitor Nikkomycin Z. To determine how differential expression of genes is related to these diverse cell wall phenotypes, we analyzed the global mRNA expression profile of myo1 Delta strains. Results: Global mRNA expression profiles of myo1 Delta strains and their corresponding wild type controls were obtained by hybridization to yeast oligonucleotide microarrays. Results for selected genes were confirmed by real time RT-PCR. A total of 547 differentially expressed genes (p < 0.01) were identified with 263 up regulated and 284 down regulated genes in the myo1 Delta strains. Gene set enrichment analysis revealed the significant over-representation of genes in the protein biosynthesis and stress response categories. The SLT2/MPK1 gene was up regulated in the microarray, and a myo1 Delta slt2 Delta double mutant was non-viable. Overexpression of ribosomal protein genes RPL30 and RPS31 suppressed the hypersensitivity to Nikkomycin Z and increased the levels of phosphorylated Slt2p in myo1 Delta strains. Increased levels of phosphorylated Slt2p were also observed in wild type strains under these conditions. Conclusion: Following this analysis of global mRNA expression in yeast myo1 Delta strains, we conclude that 547 genes were differentially regulated in myo1 Delta strains and that the stress response and protein biosynthesis gene categories were coordinately regulated in this mutant. The SLT2/MPK1 gene was confirmed to be essential for myo1 Delta strain viability, supporting that the up regulated stress response genes are regulated by the PKC1 cell integrity pathway. Suppression of Nikkomycin Z hypersensitivity together with Slt2p phosphorylation was caused by the overexpression of ribosomal protein genes RPL30 and RPS31. These ribosomal protein mRNAs were down regulated in the myo1 Delta arrays, suggesting that down regulation of ribosomal biogenesis may affect cell integrity in myo1. strains.