Jumeaux, a novel Drosophila winged-helix family protein, is required for generating asymmetric sibling neuronal cell fates.

The great majority of neurons in the Drosophila embryonic CNS are generated through two successive asymmetric cell divisions; neuroblasts (NBs) divide to produce another NB and a smaller ganglion mother cell (GMC); GMCs divide to generate two sibling neurons which can adopt distinct identities. During the division of the first born GMC from the NB4-2 lineage, GMC4-2a, Inscuteable (Insc) is localised to the apical cortex, Pon/Numb is localised to the basal cortex and two daughters with distinct identities, the RP2 motoneuron and its sibling RP2sib, are born. Resolution of distinct sibling neuronal fates requires correct apical localisation of Insc to facilitate the asymmetric localisation and preferential segregation of Pon/Numb to the basal daughter destined to become RP2. Here we report that jumeaux (jumu), which encodes a new member of the winged-helix family of transcription factors, is required to mediate the asymmetric localisation and segregation of Pon/Numb but is dispensable for Insc apical localisation during the GMC4-2a cell division. In jumu mutants GMC4-2a Pon/Numb asymmetric localisation is defective and both daughter neurons can adopt the RP2 identity. Jumu protein shows nuclear localisation and within the NB4-2 lineage is first detected only after the first neuroblast cell division, in GMC4-2a. Our results suggest that in addition to the correct formation of an apical complex, transcription mediated by Jumu is also necessary to facilitate the correct asymmetric localisation and segregation of Pon/Numb.