A genetic screen to identify factors that regulate expression from maternal nanos mRNA in Drosophila. Y. Song¹, R.P. Wharton^{1, 2}. 1) Dept Mol Genet & Microbio, Duke University, Durham, NC; 2) Howard Hughes Medical Institute.

   In Drosophila embryo, localization and translational activation of nanos (nos) mRNA at the posterior pole are essential for abdomen formation and germ cell migration. While recent studies demonstrate that the initial step in nos localization involves a diffusion and entrapment mechanism, little is known about the factors that anchor nos mRNA. Even less is known about nos translational activation, which overcomes repression at the posterior. Our aim is to identify and characterize nos localization and translational activation factors. We carried out a genetic screen in a sensitized background for mutants that affect Nos-dependent abdominal segmentation in the embryos. Using this approach, we isolated new alleles of two genes known to be involved in abdominal formation, pumilio and spindle-E, validating the premise of this screen. More importantly, we recovered five novel complementation groups. One of these, 966, appears to be a good candidate for a nos localization factor. In 966* heterozygous mutants, a modified nos mRNA is inefficiently localized and little Nos activity accumulates. The 966 gene acts downstream of Oskar, a key component for recruiting nos mRNA to the posterior pole of embryo, suggesting a relatively late role for 966 in nos localization. We are currently mapping 966 as well as the other 4 mutants recovered in the screen.