Figure 10.—

Model for regulation of meiotic progression by the Spo1 lipase. The model proposes that a reduction in PI [and PI(4)P] levels below a critical threshold is required for progression of meiosis at MI, MII, and spore formation. This implies that at higher levels PIPs negatively regulate the process. The decrease can be achieved by Spo1 or in part by other PI-specific lipases (such as Plb3) and/or high-copy expression of GPI-anchored proteins, which utilize PI for their anchor synthesis. In this model, the accumulation of Lyso-PI and fatty acids (products of PLB activity) may also serve as positive signals for meiotic progression. Other components of this pathway identified by genetic (Spo14 and Spo19) and physical (Spo23) interaction studies are indicated at the stages where they are thought to function in meiosis (see text for details).