Pattern Formation: Gurken meets torpedo for the first time

AbstractIntercellular communication between oocyte and follicle cells, mediated by the gurken–torpedo/DER signalling pathway, has a crucial role in determining both anterior–posterior and dorsal–ventral polarity in Drosophila

The translational repressors Nanos and Pumilio have divergent effects on presynaptic terminal growth and postsynaptic glutamate receptor subunit composition

Pumilio (Pum) is a translational repressor that binds selectively to target mRNAs and recruits Nanos (Nos) as a corepressor. In the larval neuromuscular system, Pum represses expression of the translation factor eIF-4E and the glutamate receptor subunit GluRIIA. Here, we show that Nos, like Pum, is expressed at the neuromuscular junction (NMJ) and in neuronal cell bodies. Surprisingly, however, Nos and Pum have divergent functions on both the presynaptic and postsynaptic sides of the NMJ. In nos mutant and nos RNA interference larvae, the number of NMJ boutons is increased, whereas loss of Pum reduces the bouton number. On the postsynaptic side, Nos acts in opposition to Pum in regulating the subunit composition of the glutamate receptor. NMJ active zones are associated with GluRIIA- and GluRIIB-containing receptor clusters. Loss of Nos causes downregulation of GluRIIA and increases the levels of GluRIIB. Consistent with this finding, the electrophysiological properties of NMJs lacking postsynaptic Nos suggest that they use primarily GluRIIB-containing receptors. Nos can regulate GluRIIB in the absence of GluRIIA, suggesting that the effects of Nos on GluRIIB levels are at least partially independent of synaptic competition between GluRIIA and GluRIIB. Nos is a target for Pum repression, and Pum binds selectively to the 3' untranslated regions of the nos and GluRIIA mRNAs. Our results suggest a model in which regulatory interplay among Pum, Nos, GluRIIA, and GluRIIB could cause a small change in Pum activity to be amplified into a large shift in the balance between GluRIIA and GluRIIB synapses

Combinatorial use of translational co-factors for cell type-specific regulation during neuronal morphogenesis in Drosophila

AbstractThe translational regulators Nanos (Nos) and Pumilio (Pum) work together to regulate the morphogenesis of dendritic arborization (da) neurons of the Drosophila larval peripheral nervous system. In contrast, Nos and Pum function in opposition to one another in the neuromuscular junction to regulate the morphogenesis and the electrophysiological properties of synaptic boutons. Neither the cellular functions of Nos and Pum nor their regulatory targets in neuronal morphogenesis are known. Here we show that Nos and Pum are required to maintain the dendritic complexity of da neurons during larval growth by promoting the outgrowth of new dendritic branches and the stabilization of existing dendritic branches, in part by regulating the expression of cut and head involution defective. Through an RNA interference screen we uncover a role for the translational co-factor Brain Tumor (Brat) in dendrite morphogenesis of da neurons and demonstrate that Nos, Pum, and Brat interact genetically to regulate dendrite morphogenesis. In the neuromuscular junction, Brat function is most likely specific for Pum in the presynaptic regulation of bouton morphogenesis. Our results reveal how the combinatorial use of co-regulators like Nos, Pum and Brat can diversify their roles in post-transcriptional regulation of gene expression for neuronal morphogenesis

The nanos translational control element represses translation in somatic cells by a Bearded box-like motif

AbstractDevelopmental control of translation is frequently mediated by regulatory elements that reside within 3′ untranslated regions (3′ UTRs). Two stem-loops within the nanos 3′ UTR translational control element (TCE) act independently to direct translational repression of maternal nanos mRNA in the ovary or embryo. We have previously shown that the nanos TCE can also function in select somatic sites. Using an ectopic expression screen, we now identify a new site of TCE function, the dorsal pouch epithelium. Analysis of TCE mutants reveals that TCE activity in the dorsal pouch does not depend on either of the stem-loops required for maternal TCE function, but instead requires a third feature—a sequence that closely matches the Bearded box, a regulatory motif found in the 3′ UTRs of several Notch pathway genes. In addition, we identify pleiohomeotic mRNA as an endogenous candidate for regulation by Bearded box-like motifs in the dorsal pouch. Together, these results suggest that the TCE has appropriated a conserved regulatory motif to expand its function to somatic tissues

bicoid mRNA localises to the Drosophila oocyte anterior by random Dynein-mediated transport and anchoring.

bicoid mRNA localises to the Drosophila oocyte anterior from stage 9 of oogenesis onwards to provide a local source for Bicoid protein for embryonic patterning. Live imaging at stage 9 reveals that bicoid mRNA particles undergo rapid Dynein-dependent movements near the oocyte anterior, but with no directional bias. Furthermore, bicoid mRNA localises normally in shot2A2, which abolishes the polarised microtubule organisation. FRAP and photo-conversion experiments demonstrate that the RNA is stably anchored at the anterior, independently of microtubules. Thus, bicoid mRNA is localised by random active transport and anterior anchoring. Super-resolution imaging reveals that bicoid mRNA forms 110-120 nm particles with variable RNA content, but constant size. These particles appear to be well-defined structures that package the RNA for transport and anchoring

Plasticity of Drosophila germ granules during germ cell development.

Compartmentalization of RNAs and proteins into membraneless structures called granules is a ubiquitous mechanism for organizing and regulating cohorts of RNAs. Germ granules are ribonucleoprotein (RNP) assemblies required for germline development across the animal kingdom, but their regulatory roles in germ cells are not fully understood. We show that after germ cell specification, Drosophila germ granules enlarge through fusion and this growth is accompanied by a shift in function. Whereas germ granules initially protect their constituent mRNAs from degradation, they subsequently target a subset of these mRNAs for degradation while maintaining protection of others. This functional shift occurs through the recruitment of decapping and degradation factors to the germ granules, which is promoted by decapping activators and renders these structures P body-like. Disrupting either the mRNA protection or degradation function results in germ cell migration defects. Our findings reveal plasticity in germ granule function that allows them to be repurposed at different stages of development to ensure population of the gonad by germ cells. Additionally, these results reveal an unexpected level of functional complexity whereby constituent RNAs within the same granule type can be differentially regulated