Fig. 4
PP2A-Tws promotes the localization of Polo to microtubules during karyokinesis in syncytial embryos. (A) PP2A-B55/Tws is inhibited by phosphorylated Endos during mitotic entry. During mitotic exit, PP2A-B55/Tws is reactivated when Endos is dephosphorylated. See text for more details. B-C. Injection of a phosphopeptide from Endos (pENDOS) to inhibit PP2A-Tws causes the mislocalization of GFP-Polo-GFP to the central spindle during karyokinesis. (B) Experimental scheme. (C) Transgenic embryos expressing GFP-Polo and H2A-RFP were imaged immediately after injection. T0: immediately before anaphase onset. After control injection (PBS only, top) during metaphase, GFP-Polo is faintly localized to microtubules already in metaphase (white arrowhead) and becomes concentrated on the central spindle after anaphase (yellow arrowhead). After injection of the pENDOS phospho-peptide, the localization of GFP-Polo to microtubules is strongly reduced (white arrow). In addition, GFP-Polo accumulates on the central spindle later, at the midbody core (yellow arrow). Scale bar: 5 μm