Comparison of phenotypes between different vangl2 mutants demonstrates dominant effects of the Looptail mutation during hair cell development

Experiments utilizing the Looptail mutant mouse, which harbors a missense mutation in the vangl2 gene, have been essential for studies of planar polarity and linking the function of the core planar cell polarity proteins to other developmental signals. Originally described as having dominant phenotypic traits, the molecular interactions underlying the Looptail mutant phenotype are unclear because Vangl2 protein levels are significantly reduced or absent from mutant tissues. Here we introduce a vangl2 knockout mouse and directly compare the severity of the knockout and Looptail mutant phenotypes by intercrossing the two lines and assaying the planar polarity of inner ear hair cells. Overall the vangl2 knockout phenotype is milder than the phenotype of compound mutants carrying both the Looptail and vangl2 knockout alleles. In compound mutants a greater number of hair cells are affected and changes in the orientation of individual hair cells are greater when quantified. We further demonstrate in a heterologous cell system that the protein encoded by the Looptail mutation (Vangl2(S464N)) disrupts delivery of Vangl1 and Vangl2 proteins to the cell surface as a result of oligomer formation between Vangl1 and Vangl2(S464N), or Vangl2 and Vangl2(S464N), coupled to the intracellular retention of Vangl2(S464N). As a result, Vangl1 protein is missing from the apical cell surface of vestibular hair cells in Looptail mutants, but is retained at the apical cell surface of hair cells in vangl2 knockouts. Similarly the distribution of Prickle-like2, a putative Vangl2 interacting protein, is differentially affected in the two mutant lines. In summary, we provide evidence for a direct physical interaction between Vangl1 and Vangl2 through a combination of in vitro and in vivo approaches and propose that this interaction underlies the dominant phenotypic traits associated with the Looptail mutation.     

Hexose uptake as an indicator of JB6 mouse epidermal cell resistance to the mitogenic activity of TPA

JB6 mouse epidermal cells have been selected for resistance to the tumor-promoting phorbol diester TPA for (1) the plateau density mitogenic (M) response, and (2) the promotion of tumor cell phenotype (P) response. The purpose of this study was to determine the relationship of hexose uptake to the two TPA-dependent processes. Monolayers of JB6 mouse epidermal cells showing one of four different phenotypes (M + P+, M + P?, M? P+, M? P?) were exposed to 60 nM [³H(G)]2 deoxy-D-glucose (2DG) with or without TPA (10 ng/ml) stimulation. The TPA mitogen-sensitive (M + P +/?) cells, when in logarithmic growth, had a lower basal 2DG uptake rate than TPA mitogen-resistant (M? P +/?) cells. At plateau density, however, only the M+P+ cells had a significantly lower basal rate. The M + (TPA mitogen-sensitive) cells (with low basal rates), when preincubated with TPA, exhibited a two to threefold increase in 2DG uptake, while the M? (TPA mitogen-resistant) lines, which already showed elevated rates, remained unchanged. There was also a positive association between TPA mitogen sensitivity and slower growth rate. These results suggest that low hexose sugar uptake is related to TPA mitogen sensitivity, but not to promotion sensitivity. Hence the cell's ability to increase its uptake rate may be required for the cells to respond to mitogenic stimulation by TPA.