James P Mahaffey

Publications (2)16.28 Total impact

• Article: Cofilin and Vangl2 cooperate in the initiation of planar cell polarity in the mouse embryo.

  James P Mahaffey, Joaquim Grego-Bessa, Karel F Liem, Kathryn V Anderson
  [show abstract] [hide abstract]
  ABSTRACT: The planar cell polarity (PCP; non-canonical Wnt) pathway is required to orient the cells within the plane of an epithelium. Here, we show that cofilin 1 (Cfl1), an actin-severing protein, and Vangl2, a core PCP protein, cooperate to control PCP in the early mouse embryo. Two aspects of planar polarity can be analyzed quantitatively at cellular resolution in the mouse embryo: convergent extension of the axial midline; and posterior positioning of cilia on cells of the node. Analysis of the spatial distribution of brachyury(+) midline cells shows that the Cfl1 mutant midline is normal, whereas Vangl2 mutants have a slightly wider midline. By contrast, midline convergent extension fails completely in Vangl2 Cfl1 double mutants. Planar polarity is required for the posterior positioning of cilia on cells in the mouse node, which is essential for the initiation of left-right asymmetry. Node cilia are correctly positioned in Cfl1 and Vangl2 single mutants, but cilia remain in the center of the cell in Vangl2 Cfl1 double mutants, leading to randomization of left-right asymmetry. In both the midline and node, the defect in planar polarity in the double mutants arises because PCP protein complexes fail to traffic to the apical cell membrane, although other aspects of apical-basal polarity are unaffected. Genetic and pharmacological experiments demonstrate that F-actin remodeling is essential for the initiation, but not maintenance, of PCP. We propose that Vangl2 and cofilin cooperate to target Rab11(+) vesicles containing PCP proteins to the apical membrane during the initiation of planar cell polarity.
  Development 03/2013; 140(6):1262-71. · 6.60 Impact Factor
• Article: Tissue-specific roles of Axin2 in the inhibition and activation of Wnt signaling in the mouse embryo.

  Lihui Qian, James P Mahaffey, Heather L Alcorn, Kathryn V Anderson
  [show abstract] [hide abstract]
  ABSTRACT: Axin proteins are key negative regulators of the canonical Wnt signal transduction pathway. Although Axin2 null mice are viable, we identified an unusual ENU-induced recessive allele of Axin2, canp, that causes midgestation lethality in homozygotes. We show that the Axin2(canp) mutation is a V26D substitution in an invariant N-terminal sequence motif and that the Axin2(canp) protein is more stable than wild type. As predicted for an increased level of a negative regulator, the Axin2(canp) mutation leads to decreased Wnt signaling in most tissues, and this can account for most of the morphological phenotypes of Axin2(canp) mutants. In contrast, there is a paradoxical increase in canonical Wnt activity in the late primitive streak of all Axin2(canp) mutant embryos that is associated with the formation of an ectopic tail in some mutants. Treatment of wild-type embryos with an inhibitor of Tankyrase that stabilizes Axin proteins also causes inhibition of Wnt signaling in anterior regions of the embryo and a gain of Wnt signaling in the primitive streak. The results indicate that although increased stability of Axin2 leads to a loss of canonical Wnt signaling in most tissues, stabilized Axin2 enhances Wnt pathway activity in a specific progenitor population in the late primitive streak.
  Proceedings of the National Academy of Sciences 05/2011; 108(21):8692-7. · 9.68 Impact Factor