Phosphotyrosyl phosphatase activator facilitates Miranda localization through dephosphorylation in dividing neuroblasts

Abstract

The mechanism for the basal targeting of the Miranda (Mira) complex during the asymmetric division of Drosophila neuroblasts (NBs) is yet to be fully understood. We have identified conserved Phosphotyrosyl phosphatase activator (PTPA) as a novel mediator for the basal localization of the Mira complex in larval brain NBs. In mutant Ptpa NBs, Mira remains cytoplasmic during early mitosis and its basal localization is delayed until anaphase. Detailed analyses indicate that PTPA acts independent of and before aPKC to localize Mira. Mechanistically, our data show that the phosphorylation status of the T591 residue determines the subcellular localization of Mira and that PTPA facilitates the dephosphorylation of T591. Furthermore, PTPA associates with the Protein phosphatase 4 complex to mediate localization of Mira. On the basis of these results, a two-step process for the basal localization of Mira during NB division is revealed: cortical association of Mira mediated by the PTPA-PP4 complex is followed by apical aPKC-mediated basal restriction.

aPKC-mediated displacement and actomyosin-mediated retention polarize Miranda inDrosophilaneuroblasts

“…The transition from uniform PM binding to asymmetric basal localization is triggered from prophase, where aPKC activity removes Mira’s ability to bind the PM uniformly ( Figure1, 4 ). NEB appears to be a critical time point for basal crescent formation ( Figure 1 ), which is in line with the recent finding that factors released from the nucleus upon NEB are involved in regulating Mira localization (Zhang et al 2016).…”

Protein phosphatase 4 coordinates glial membrane recruitment and phagocytic clearance of degenerating axons in Drosophila

“…21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 32, 36, 37, 38, 39 Our work now highlights a previously unexplored role for PP4 in governing innate glial immune responses to neurodegeneration and poses interesting questions for future efforts aimed at understanding precisely how PP4 activity promotes cell migration. We show that forced SOS GEF expression rescues loss of PP4c (Figures 7a–i), implicating the SOS GEF complex as one key effector downstream of PP4 required for proper Rac1 activity in responding glia.…”

“…21, 22, 23, 24, 25, 26, 27, 28 The PP4 complex consists of three subunits: one catalytic subunit (PP4c), which is required for dephosphorylation of target proteins, and two regulatory subunits (PP4r2 and Falafel/PP4r3), which control subcellular localization of the complex and specificity of phosphatase target association. 21, 29 Interestingly, PP4 is also linked to cell motility and tumor invasiveness in several organisms and cell types.…”

The Protein Phosphatase 4 complex promotes the Notch pathway andwinglesstranscription

“…4D, S2H). Although aPKC is involved with PP4 and Notch signaling in ACD (Sousa-Nunes et al, 2009; Zhang et al, 2016), it does not appear to be directly involved in Notch signaling and pattering in the developing wing imaginal disc.…”