The orb gene of Drosophila encodes sex-specific genn-line proteins that contain two RRM-type RNA-binding domains. Here we report the distribution of Orb protein in wild-type, tumorous, and orb mutant ovaries. The wild-type distribution of Orb protein during oogenesis resembles that of its RNA, preferentially accumulating in the cytoplasm of the developing oocyte shortly after the formation of the 16-cell cyst. As anticipated from its germ-line expression, mutations in orb lead to female sterility. Analysis of the effect of orb mutants on the distribution of RNAs known to be required for oocyte differentiation and polarity suggests that orb functions in RNA localization at multiple points during oogenesis. In addition, phenotypic characterization of the orb mutants indicates that the gene is required early in oogenesis for formation of the 16-cell cyst. It then functions in the differentiation of the oocyte and is required for the three-dimensional reorganization of the germ cells in the cyst as well as for the establishment of normal germ-line-soma interactions in the egg chamber.

Abstract. Coordination of cellular organization requires the interaction of the cytoskeletal filament systems. Recently, several lines of investigation have suggested that transport of cellular components along both microtubules and actin filaments is important for cellular organization and function. We report here on molecules that may mediate coordination between the actin and microtubule cytoskeletons. We have identified a 195-kD protein that coimmunoprecipitates with a class VI myosin, Drosophila 95F unconventional myosin. Cloning and sequencing of the gene encoding the 195-kD protein reveals that it is the first homologue identified of cytoplasmic linker protein (CLIP)–170, a protein that links endocytic vesicles to microtubules. We have named this protein D-CLIP-190 (the predicted molecular mass is 189 kD) based on its similarity to CLIP-170 and its ability to cosediment with microtubules. The similarity between D-CLIP-190 and CLIP-170 extends throughout the length of the proteins, and they have a number of predicted sequence and structural features in common. 95F myosin and D-CLIP-190 are coexpressed in a number of tissues during embryogenesis in Drosophila. In the axonal processes of neurons, they are colocalized in the same particulate structures, which resemble vesicles. They are also colocalized at the posterior pole of the early embryo, and this localization is dependent on the actin cytoskeleton. The association of a myosin and a homologue of a microtubule-binding protein in the nervous system and at the posterior pole, where both microtubule and actin-dependent processes are known to be important, leads us to speculate that these two proteins may functionally link the actin and microtubule cytoskeletons.

IL-15 mRNA levels are increased in diseases caused by human T cell lymphotropic virus type I (HTLV-I). In this study, we demonstrated that IL-15Rα, the IL-15-specific binding receptor, mRNA and protein levels were also elevated in HTLV-I-infected cells. We showed that transient HTLV-I Tax expression lead to increased IL-15Rα mRNA levels. In addition, by using a reporter construct that bears the human IL-15Rα promoter, we demonstrated that Tax expression increased promoter activity by at least 4-fold. Furthermore, using promoter deletion constructs and gel shift analysis, we defined a functional NF-κB-binding motif in the human IL-15Rα promoter, suggesting that Tax activation of IL-15Rα is due, in part, to the induction of NF-κB. These data indicate that IL-15Rα is transcriptionally regulated by the HTLV-I Tax protein through the action of NF-κB. These findings suggest a role for IL-15Rα in aberrant T cell proliferation observed in HTLV-I-associated diseases.

Localization of mRNAs is one of many aspects of cellular organization that requires the cytoskeleton. In Drosophila, microtubules are known to be required for correct localization of developmentally important mRNAs and proteins during oogenesis; however, the role of the actin cytoskeleton in localization is less clear. Furthermore, it is not known whether either of these cytoskeletal systems are necessary for maintenance of RNA localization in the early embryo. We have examined the contribution of the actin and microtubule cytoskeletons to maintenance of RNA and protein localization in the early Drosophila embryo. We have found that while microtubules are not necessary, the actin cytoskeleton is needed for stable association of nanos, oskar, germ cell-less and cyclin B mRNAs and Oskar and Vasa proteins at the posterior pole in the early embryo. In contrast, bicoid RNA, which is located at the anterior pole, does not require either cytoskeletal system to remain at the anterior.