title: Drosophila patterning is established by differential association of mRNAs with P bodies.
abstract: The primary embryonic axes in flies, frogs and fish are formed through translational regulation of localized transcripts before fertilization. In Drosophila melanogaster, the axes are established through the transport and translational regulation of gurken (grk) and bicoid (bcd) messenger RNA in the oocyte and embryo. Both transcripts are translationally silent while being localized within the oocyte along microtubules by cytoplasmic dynein. Once localized, grk is translated at the dorsoanterior of the oocyte to send a TGF-α signal to the overlying somatic cells. In contrast, bcd is translationally repressed in the oocyte until its activation in early embryos when it forms an anteroposterior morphogenetic gradient. How this differential translational regulation is achieved is not fully understood. Here, we address this question using ultrastructural analysis, super-resolution microscopy and live-cell imaging. We show that grk and bcd ribonucleoprotein (RNP) complexes associate with electron-dense bodies that lack ribosomes and contain translational repressors. These properties are characteristic of processing bodies (P bodies), which are considered to be regions of cytoplasm where decisions are made on the translation and degradation of mRNA. Endogenous grk mRNA forms dynamic RNP particles that become docked and translated at the periphery of P bodies, where we show that the translational activator Oo18 RNA-binding protein (Orb, a homologue of CEPB) and the anchoring factor Squid (Sqd) are also enriched. In contrast, an excess of grk mRNA becomes localized inside the P bodies, where endogenous bcd mRNA is localized and translationally repressed. Interestingly, bcd mRNA dissociates from P bodies in embryos following egg activation, when it is known to become translationally active. We propose a general principle of translational regulation during axis specification involving remodelling of transport RNPs and dynamic partitioning of different transcripts between the translationally active edge of P bodies and their silent core.
authors.affiliation: Department of Biochemistry, The University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Timothy T
authors.initials: TT
authors.lastname: Weil
authors.forename: Richard M
authors.initials: RM
authors.lastname: Parton
authors.forename: Bram
authors.initials: B
authors.lastname: Herpers
authors.forename: Jan
authors.initials: J
authors.lastname: Soetaert
authors.forename: Tineke
authors.initials: T
authors.lastname: Veenendaal
authors.forename: Despina
authors.initials: D
authors.lastname: Xanthakis
authors.forename: Ian M
authors.initials: IM
authors.lastname: Dobbie
authors.forename: James M
authors.initials: JM
authors.lastname: Halstead
authors.forename: Rippei
authors.initials: R
authors.lastname: Hayashi
authors.forename: Catherine
authors.initials: C
authors.lastname: Rabouille
authors.forename: Ilan
authors.initials: I
authors.lastname: Davis
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000196:embryology* / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D017404:In Situ Hybridization, Fluorescence; D008854:Microscopy, Electron; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D016211:Transforming Growth Factor alpha / Q000235:genetics / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D015534:Trans-Activators; D016211:Transforming Growth Factor alpha; C056478:bcd protein, Drosophila; C083730:grk protein, Drosophila; C089932:orb protein, Drosophila; C081480:sqd protein, Drosophila