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Open Access Research article

The Drosophila IKK-related kinase (Ik2) and Spindle-F proteins are part of a complex that regulates cytoskeleton organization during oogenesis

Dikla Dubin-Bar1, Amir Bitan1, Anna Bakhrat1, Rotem Kaiden-Hasson2, Sharon Etzion3, Boaz Shaanan2 and Uri Abdu1*

  • * Corresponding author: Uri Abdu abdu@bgu.ac.il

  • † Equal contributors

Author Affiliations

1 Department of Life Science, National Institute for Biotechnology in the Negev, Ben-Gurion University, Beer-Sheva, 84105 Israel

2 Department of Life Science, Ben-Gurion University, Beer-Sheva, 84105 Israel

3 National Institute for Biotechnology in the Negev, Ben-Gurion University, Beer-Sheva, 84105 Israel

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BMC Cell Biology 2008, 9:51  doi:10.1186/1471-2121-9-51

Published: 17 September 2008

Abstract

Background

IkappaB kinases (IKKs) regulate the activity of Rel/NF-kappaB transcription factors by targeting their inhibitory partner proteins, IkappaBs, for degradation. The Drosophila genome encodes two members of the IKK family. Whereas the first is a kinase essential for activation of the NF-kappaB pathway, the latter does not act as IkappaB kinase. Instead, recent findings indicate that Ik2 regulates F-actin assembly by mediating the function of nonapoptotic caspases via degradation of DIAP1. Also, it has been suggested that ik2 regulates interactions between the minus ends of the microtubules and the actin-rich cortex in the oocyte. Since spn-F mutants display oocyte defects similar to those of ik2 mutant, we decided to investigate whether Spn-F could be a direct regulatory target of Ik2.

Results

We found that Ik2 binds physically to Spn-F, biomolecular interaction analysis of Spn-F and Ik2 demonstrating that both proteins bind directly and form a complex. We showed that Ik2 phosphorylates Spn-F and demonstrated that this phosphorylation does not lead to Spn-F degradation. Ik2 is localized to the anterior ring of the oocyte and to punctate structures in the nurse cells together with Spn-F protein, and both proteins are mutually required for their localization.

Conclusion

We conclude that Ik2 and Spn-F form a complex, which regulates cytoskeleton organization during Drosophila oogenesis and in which Spn-F is the direct regulatory target for Ik2. Interestingly, Ik2 in this complex does not function as a typical IKK in that it does not direct SpnF for degradation following phosphorylation.