Centrosomal and acentrosomal microtubules collaborate to direct the dorsal localisation of gurken mRNA in Drosophila oocyte. Rippei Hayashi, Mark Wainwright, Sophie Liddell, Sheena Pinchin, David Ish-Horowicz. Developmental Genetics Laboratory, London Research Institute, Cancer Research UK, London, London, United Kingdom.

   Transport of gurken (grk) mRNA along microtubules establishes the two major body-axes of the Drosophila oocyte. To investigate how microtubules are nucleated and polarised in order to pattern the oocyte, we have screened chromosome 3L for EMS-induced mutations that disrupt localisation of fluorescently-labelled grk mRNA. Mapping the causative mutations by SNP recombinational mapping and deep genomic sequencing identified molecular lesions for mutations in 9 complementation groups, affecting grk mRNA localisation, dynein transport, piRNA biogenesis, and other aspects of oogenesis. These mutations include new null alleles of armitage affecting follicle cell development. Analysis of an induced kinesin-light-chain (klc) mutant shows that klc is required for the clustering and the cortex localisation of centrosomes. We find two sites of grk mRNA localisation in the mid stage klc mutant oocytes: near the mispositioned centrosomes and adjacent to the dorsal cortex, suggesting that grk mRNA is transported on two classes of microtubules, only one of which depends on centrosomes. We also discuss how these microtubule populations establish the dorsal localisation of grk mRNA.