New phenotypes associated with the swallow gene of Drosophila: evidence for a general role in oocyte cytoskeletal organization

During oogenesis in Drosophila, several mRNAs and proteins are localized to discrete regions of the developing oocyte, resulting in a mature oocyte wi th a well-defined anterior-posterior axis. The product of the swallow (sww) gene is required for the localization of two different mRNAs during oogene sis, bicoid (bcd) and Adducin-like/hu-li tai shao (hts). We initiated a det ailed characterization of the phenotypes associated with each of eight swww alleles as a means of investigating the role of sww in oogenic patterning. RNA localization defects in various sww mutants were examined by radioacti ve in situ hybridization to paraffin sections. Using this technique, severa l previously unreported RNA localization defects have been observed. Althou gh bcd RNA localization is often lost completely in sww oocytes, in a high proportion of cases, bcd RNA is localized inappropriately along the periphe ry of the mature oocyte. In several sww mutants, a portion of the bcd mRNA population becomes concentrated at the posterior pole of the oocyte during late oogenesis. Several sww mutations also result in oskar RNA localization defects, consistent with a global role for sww in cytoskeletal regulation or organization. A detailed temporal and spatial analysis of hts RNA locali zation in sww mutants and in drug-treated ovaries reveals many similarities to bcd RNA localization, and implies the two independent localization even ts are accomplished by the same mechanism.