Figure 7.

Model of the nucleus-restricted, RNA-mediated premeiotic silencing in A. nidulans. Schematic representation of the prezygotic cell containing two haploid nuclei from a cross between two parental strains is shown. One nucleus carries duplication of the matA gene (solid bars); the other nucleus carries a single copy of matA. Gene silencing is mediated by a transgene-derived matA transcript and appears to be restricted to the nucleus of origin. The silencing effect does not spread between nuclei in the common cytoplasm of the syncytium or dikaryon. Therefore, a parental nucleus with a single wild-type matA gene retains active mat function that is fully able to complement the silenced matA function of the other parental nucleus, resulting in a wild-type sexual phenotype. Framed box with dashed line indicates a potential cytoplasmic compartment that might contribute to nucleus-restricted MatIS in the prezygotic cell. Refer to Discussion for details.