Par-1 regulates bicoid mRNA localisation by phosphorylating Exuperantia.
The Ser/Thr kinase Par-1 is required for cell polarisation in diverse organisms such as yeast, worms, flies and mammals. During Drosophila oogenesis, Par-1 is required for several polarisation events, including localisation of the anterior determinant bicoid. To elucidate the molecular pathways triggered by Par-1, we have performed a genome-wide, high-throughput screen for Par-1 targets. Among the targets identified in this screen was Exuperantia (Exu), a mediator of bicoid mRNA localisation. We show that Exu is a phosphoprotein whose phosphorylation is dependent on Par-1 in vitro and in vivo. We identify two motifs in Exu that are phosphorylated by Par-1, and show that their mutation abolishes bicoid mRNA localisation during mid-oogenesis. Interestingly, exu mutants in which Exu phosphorylation is specifically affected can to some extent recover from these bicoid mRNA localisation defects during late oogenesis. These results demonstrate that Par-1 establishes polarity in the oocyte by activating a mediator of bicoid mRNA localisation. Furthermore, our analysis reveals two phases of Exu-dependent bicoid mRNA localisation: an early phase that is strictly dependent on Exu phosphorylation and a late phase that is less phosphorylation dependent.
Riechmann
Veit
V
European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
Ephrussi
Anne
A
D020816:Amino Acid Motifs; D000818:Animals; D015153:Blotting, Western; D029721:Drosophila Proteins / Q000378:metabolism* / Q000502:physiology*; D004331:Drosophila melanogaster / Q000196:embryology / Q000235:genetics; D004527:Egg Proteins / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004625:Embryo, Nonmammalian; D020224:Expressed Sequence Tags; D005260:Female; D018507:Gene Expression Regulation, Developmental; D038362:Glycogen Synthase Kinase 3; D018398:Homeodomain Proteins / Q000378:metabolism*; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence; D008957:Models, Genetic; D016296:Mutagenesis; D009154:Mutation; D010053:Ovary / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism*; D019076:Transgenes
D029721:Drosophila Proteins; D004527:Egg Proteins; D018398:Homeodomain Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D015534:Trans-Activators; C056478:bcd protein, Drosophila; C072067:exu protein, Drosophila; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D038362:Glycogen Synthase Kinase 3; C472496:Par-1 protein, Drosophila