Figure 6. A model for the development of and the escape from pica.
The pica phenotype is generated by the expression and presumable aggregation of Q56-YFP (yellow) and the subsequent inability of cells to follow the normal haploid growth cycle, potentially caused by compromised septin deposition (green). Deletion of Group I genes and treatment with GdnHCl restores growth as haploid yeast cells and septin ring assembly. An alternative route is switching to diploid growth, which under normal conditions is blocked by Group II (and Group III) genes. This switching event happens for Group II genes only in response to the cytostatic pressure from Q56-YFP. In deletion strains for Group III genes, this switching to 2N states happens also under control conditions, leading to constitutive cycling at higher ploidy and resistance to pica, as well as a restored capability to assemble septin rings.