Abstract
Regulation of microtubule polarization is an important aspect of establishing body axes during
Drosophila
oocyte development. Siomi and colleagues identify the Maelstrom protein (mael) as an essential player in MTOC establishment. Mael forms specific complexes with MTOC components, and its mutation leads to their mislocalization and centrosome segregation defects.
The establishment of body axes in multicellular organisms requires accurate control of microtubule polarization. Mutations in
Drosophila
PIWI-interacting RNA (piRNA) pathway genes often disrupt the axes of the oocyte. This results from the activation of the DNA damage checkpoint factor Checkpoint kinase 2 (Chk2) due to transposon derepression. A piRNA pathway gene,
maelstrom
(
mael
), is critical for the establishment of oocyte polarity in the developing egg chamber during
Drosophila
oogenesis. We show that Mael forms complexes with microtubule-organizing center (MTOC) components, including Centrosomin, Mini spindles, and γTubulin. We also show that Mael colocalizes with αTubulin and γTubulin to centrosomes in dividing cyst cells and follicle cells. MTOC components mislocalize in
mael
mutant germarium and egg chambers, leading to centrosome migration defects. During oogenesis, the loss of
mael
affects oocyte determination and induces egg chamber fusion. Finally, we show that the axis specification defects in
mael
mutants are not suppressed by a mutation in
mnk
, which encodes a Chk2 homolog. These findings suggest a model in which Mael serves as a platform that nucleates other MTOC components to form a functional MTOC in early oocyte development, which is independent of Chk2 activation and DNA damage signaling.