An early event in the development of multicellular organisms is the establishment of the anteroposterior (AP) and dorsoventral (DV) axes. In Drosophila embryos, the asymmetric localisation of maternal mRNAs,such as gurken (grk) and oskar (osk)mRNAs, is essential for the formation of these axes. mRNA localisation requires an organised microtubule network, and in this issue of Development two papers investigate how microtubules are organised in Drosophila oocytes. On p. , Trudi Schüpbach and colleagues identify a new protein – Spn-F –that affects microtubule organisation and axis determination during Drosophila oogenesis. spn-F was originally identified as a mutation that affects the DV polarity of the eggshell. The researchers now report that, in spn-F mutants, changes in the pattern of the eggshell are due to defects in the localisation of grk mRNA during mid-oogenesis. These arise because of defects in the organisation of the microtubules that move grk mRNA around the oocyte. spn-F,the authors report, encodes a coiled-coil protein that localises to the minus end of oocyte microtubules, where it might, for example, be required for the transport of grk RNA along microtubules. On p. , Shapiro and Anderson report that Drosophila Ik2 is also required for mRNA localisation during oogenesis, and that it helps to link microtubule minus ends to the oocyte cortex. Ik2 is an IκB kinase, which the researchers expected to regulate the localisation of the early patterning determinant Dorsal, an NF-κB transcription factor. Instead, ik2 is essential for the correct localisation of osk and grk mRNAs in oocytes; its absence produces bicaudal and ventralised embryos that closely resemble spn-F mutant embryos. In these mutant embryos, abnormal mRNA localisation is accompanied by defects in the organisation of microtubule minus ends and the oocyte actin cytoskeleton. Interestingly, given the similarities between ik2 and spn-F mutants, both as embryos and as adults, Schüpbach and colleagues show that Spn-F and Ik2 interact directly in a global two-hybrid screen. Both research teams suggest,therefore, that these proteins might cooperate to organise microtubules during Drosophila oogenesis to ensure that axis determination goes smoothly.
