REQUIREMENT FOR DROSOPHILA CYTOPLASMIC TROPOMYOSIN IN OSKAR MESSENGER-RNA LOCALIZATION

THE localization of oskar (osk) RNA to the posterior pole of the devel oping fruit fly (Drosophila) oocyte induces the assembly of pole plasm , causing development of tbe abdomen and germ line(1,2). Failure to lo calize oskar RNA results in embryos that lack abdomen and germ cells. Conversely, mis-targeting of oskar RNA to the anterior of the oocyte c auses formation of ectopic abdomen and germ cells at the anterior pole (3). Maternal mutants that have reduced pole plasm activity produce st erile adults with normal abdominal development, suggesting that germ c ells are more sensitive than abdomen to defects in pole plasm assembly (4). Thus mutations in genes that reduce oskar RNA localization or act ivity can be recovered as viable sterile adults. In a screen for mutan ts defective in germ cell formation, we isolated nine alleles of the t ropomyosin II gene(5). Here we show that mutations in tropomyosin II ( TmII) virtually abolish oskar RNA localization to the posterior pole, suggesting an involvement of the actin network in oskar RNA localizati on.