1. Linking Cell Cycle to Asymmteric Division: Aurora-A phosphorylates the Par Complex to Regulate Numb Localization Frederik Wirtz-Peitz, Takashi Nishimura and Juergen A. Knoblich Cell, 136, 161-173, 2008

2. Cells divide into two daughters of different fates Extrinsic and intrinsic regulation of asymmetric cell division Cells segregate cell fate determinants  Numb Drosophila larvael brain: balances differentiation /self renewal Asymmetric cell division Introduction

3. Controls integrin endocytosis Repressor of Notch signaling Cell fate determinant in asymmetric cell division  numb mutant neuroblasts divide symmetrically into two neuroblasts (Lee et al., 2006) Par complex provides spatial cue for Numb localization:  Phosphorylation by aPKC releases Numb into the cytoplasm  Numb and aPKC localize to opposite sites of the dividing cell The cell fate determinant Numb Introduction www.biologie.ens.fr/desnpcs/IMG/jpg_fig2.jpg

4. Molecular mechanism for asymmetric localization of Numb during mitosis?  Aurora-A is required for Numb asymmetry (Berdnik and Knoblich, 2002)  Numb is mislocalized upon expression of Lgl 3A (Betschinger et al., 2003)

5. AurA activates aPKC by phosphorylating the aPKC complex aurA mutants:

6. Par6 is phosphorylated by Aur-A in vivo  AurA phosphorylates Par6 in on Ser34 in vitro and in vivo

7. Par6 phosphorylation negatively regulates its physical interaction with aPKC  AurA activates aPKC by dissociating it from Par6

8. Par6 phosphorylation controls localization of Numb during mitosis  Additional substrates for AurA?

9. Lgl is insoluble when unphosphorylated (Betschinger et al., 2003) aPKC releases Lgl from the cell cortex in mitosis

10. Aur-A is necessary and sufficient to induce cortical Lgl release

11. Baz acts downstream of Lgl  Numb asymmetry requiers Baz (= Par3; Bellaiche et al., 2001)

12. Aur-A regulates subunit composistion of the Par Complex  Lgl inhibits cortical localization of Baz  Interaction of Baz with Par6/aPKC is inhibited by Lgl  AurA triggers remodeling of Par complex

13. Numb localization requires appropiate levels of Baz complex

14. Exchange of Lgl for Baz enables the Par complex to phosphorylate Numb  Baz changes the substrate specifity of aPKC

15. Interaction of Numb with the Baz complex is essential for its asymmetric localization  numb S52F : localizes symmetrically in SOP cells can still be phosphorylated by aPKC  AurA induces asymmetric localization of Numb by promoting interaction of Numb with aPKC

16. Proposed mechanism

17. Summary Cascade of interactions that culminate in Numb asymmetric localization  Par6 is a cortical substrate for Aurora-A  Par6 phosphorylation triggers exchange of Lgl for Baz in the Par complex  Bax/Par complex phosphorylates Numb  Restict Numb into a crescent on the opposite site Lgl acts as a inhibitory subunit of the Par complex