A putative lipid-binding protein and two cyclin-dependent kinases act in a pathway coordinating nuclear divisions and gametogenesis in S. cerevisiae.
Gela G. Tevzadze, Jessica V. Pierce, Rochelle E. Esposito
Mol Genetics and Cell Biology, The University of Chicago, 920 East 58th Str, Chicago, IL, 60637, USA
We previously showed that Spo1, a meiosis-specific phospholipase B homolog, is required for progression of the nuclear divisions and spore wall development. High copy suppression by GPI (lipid-anchored) proteins and partial complementation by PLB3 (a PI-specific lipase), suggested Spo1 acts on PI to generate Lyso-PI and fatty acid signaling molecules required for progression of meiosis. This report identifies other factors in the Spo1-dependent pathway. A screen for mutant suppressors enhancing sporulation of a spo1 null recovered an allele of SPO73 (a mid-late meiosis-specific gene) suppressing the last stage where spo1 is defective. Spo73 has a Dysferlin (lipid-binding) domain, consistent with the view that it responds to lipid signals generated by Spo1. Spo73 has both positive and negative roles (separable by mutation) in sporulation: it is required for prospore membrane synthesis in Spo1 + , and for a checkpoint-like control blocking the process in Spo1 - . Two more factors, both associated with kinase activities, were found in other screens. One, a cdc28 allele, increases spore formation in spo1 spo73 strains by partially suppressing spo1 's defect in MI and MII, as well as the sporulation defect of spo73. The other, EFR3, a high copy suppressor of spo73, encodes a mitochondrial protein interacting with Pho85, a non-essential CDK. Our findings support a model in which these CDKs and Spo73 respond to a Spo1-generated lipid signal regulating successive stages of gametogenesis.