ABSTRACT
The localization of mRNAs to discrete cytoplasmic sites is important for the function of many, and perhaps all, cells. Many mRNAs are thought to be localized in a directed fashion along microtubule tracts. This appears to be the case for several mRNAs that are synthesized in Drosophila nurse cells and then transported into, and localized within, the oocyte. In this report, we compare the transport/localization kinetics and dynamics of three such mRNAs, K10, bicoid, and oskar. We generated flies carrying heat shock-K10, -bicoid, or -oskar fusion genes, which allowed us to carry out the molecular genetics equivalent of a pulse chase experiment. Our analyses indicate that K10, bicoid, and oskar mRNA transport and localization are a continuous process involving multiple movements of the same mRNA molecules. The transport and early localization dynamics of the three mRNAs are indistinguishable from each other and, in order, include accumulation in the apical regions of nurse cells, transport to the posterior pole of the oocyte, and movement to the oocyte's anterior cortex at stage 8. We also show that the rate of transport is the same in each case, approximately 1.1 microns/min. Only after stage 8 are RNA-specific movements seen. The similarities in the transport/ early localization kinetics and dynamics of K10, bicoid, and oskar mRNAs suggest that such events are mediated by a common set of factors. We also observe that all three mRNAs localize to the apical regions of somatic follicle cells when expressed in such cells, suggesting that the transport/early localization factors are widespread and involved in the localization of mRNAs in many tissues.
Subject(s)
Drosophila Proteins , Drosophila/metabolism , Homeodomain Proteins , Insect Hormones/genetics , Nuclear Proteins/genetics , Proteins/genetics , RNA, Messenger/metabolism , Trans-Activators , Animals , Biological Transport , Drosophila/embryology , Drosophila/genetics , HSP70 Heat-Shock Proteins/genetics , Kinetics , Oocytes/metabolism , Promoter Regions, Genetic , Recombinant Fusion Proteins/genetics , Transcription FactorsABSTRACT
A critical step in Drosophila dorsoventral patterning is the movement of gurken mRNA from the anterior cortex of the oocyte to the oocyte's anterodorsal corner at stage 8 of oogenesis. Such movement is dependent on fs(1)K10. It has been proposed that fs(1)K10 mediates gurken mRNA movement by down-regulating gurken mRNA levels, thus ensuring that gurken mRNA does not saturate its receptors located in the oocyte's anterodorsal corner. In contradiction to this model, we show here--both genetically and immunocytochemically--that GRK protein levels are lower in the anterodorsal region of fs(1)K10 mutant oocytes than in the anterodorsal region of fs(1)K10+ oocytes. From this and other data, we propose a more direct role for fs(1)K10 in the gurken mRNA localization process.
