Strabismus Promotes Recruitment and Degradation of Farnesylated Prickle in Drosophila melanogaster Planar Polarity Specification

Abstract

The core planar polarity proteins are required to specify the orientation of structures that are polarised in the plane of the epithelium. In the Drosophila melanogaster wing, the core proteins localise asymmetrically at either proximal or distal cell edges. Asymmetric localisation is thought to be biased by long-range cues, causing asymmetric complexes to become aligned with the tissue axes. Core proteins are then thought to participate in feedback interactions that are necessary to amplify asymmetry, and in order for such feedback interactions to operate correctly, the levels of the core proteins at junctions must be tightly regulated. We have investigated regulation of the core protein Prickle (Pk) in the pupal wing. The core protein Strabismus (Stbm) is required to recruit Pk into asymmetric complexes at proximal cell ends, and we report here that it also promotes proteasomal degradation of excess Pk, probably via a Cullin-1 dependent process. We also show for the first time that Pk is farnesylated in vivo, and this is essential for Pk function in the wing. Notably, farnesylation of Pk is necessary for it to be recruited into asymmetric complexes and function in feedback amplification, probably by reinforcing weak direct interactions between Stbm and Pk. Furthermore, farnesylation is also required for Stbm to promote proteasomal degradation of Pk. We propose that Stbm recruits farnesylated Pk into asymmetric complexes, but also promotes degradation of excess Pk that would otherwise perturb feedback amplification.

Control of vertebrate core PCP protein localization and dynamics by Prickle2

“…S4A-C). In light of previous evidence that Vang participates in the control of Pk protein levels (Strutt et al, 2013b), our results suggest that Vangl1 overexpression might be leading to increased levels of Pk2 degradation, which in turn leads to a reduction in Pk2 and to associated Dvl1 patterning defects.…”

Prickle/spiny-legs isoforms control the polarity of the apical microtubule network in planar cell polarity

“…1C,D,E). Under similar conditions, Sple tagged with green fluorescent protein (GFP) localizes to the distal side of the cell, opposite to the proximal localization of Pk in wild-type wings (Strutt et al, 2013). This is indicative of reversal of the entire core complex, as confirmed here by the clonal expression of Vang::YFP (Fig.…”

“…Overexpressing Sple in wings produces varying degrees of polarity reversal (supplementary material Fig. S1) (Gubb et al, 1999;Lee and Adler, 2002;Doyle et al, 2008;Lin and Gubb, 2009;Strutt et al, 2013). Similar dependence on a single Pk-Sple isoform is seen for A-abd, P-abd and eye (Gubb et al, 1999;Lawrence et al, 2004), and ectopic expression of the alternative isoform has been observed to produce reversals of polarity in A-abd and P-abd (Lawrence et al, 2004).…”

“…In vang mutant wings, the plus-end bias is less pronounced with or without Sple overexpression when compared with wild-type wings. We speculate that this might be because Pk-Sple is partially dependent on Vang for membrane localization (Strutt et al, 2013).…”

Prickle1 promotes focal adhesion disassembly in cooperation with CLASP-LL5β complex in migrating cells

“…Fz, Dsh and Dgo concentrate on the one face of a cell, and Stbm and Prickle1 concentrate on the opposite; Fmi is present at both. Stbm is required for the recruitment of Prickle1 at proximal cell ends in the pupa wing and promotes the degradation of excess Prickle1 to maintain its asymmetrical localization (Strutt et al, 2013). Arf1 and adaptor protein-1 (AP-1) are required for the planar polarized enrichment of core PCP proteins along the proximaldistal axis (Carvajal-Gonzalez et al, 2015).…”