Cilia are microtubule-based organelles that project into the extracellular space, function in the perception and integration of environmental cues, and regulate Hedgehog signal transduction. The emergent association of ciliary defects with diverse and pleiotropic human disorders has fuelled investigations into the molecular genetic regulation of ciliogenesis. Although recent studies implicate planar cell polarity (PCP) in cilia formation, this conclusion is based on analyses of proteins that are not specific to, or downstream effectors of PCP signal transduction. Here we characterize zebrafish embryos devoid of all Vangl2 function, a core and specific component of the PCP signalling pathway. Using Arl13b-GFP as a live marker of the ciliary axoneme, we demonstrate that Vangl2 is not required for ciliogenesis. Instead, Vangl2 controls the posterior tilting of primary motile cilia lining the neurocoel, Kupffer's vesicle and pronephric duct. Furthermore, we show that Vangl2 is required for asymmetric localization of cilia to the posterior apical membrane of neuroepithelial cells. Our results indicate a broad and essential role for PCP in the asymmetric localization and orientation of motile primary cilia, establishing directional fluid flow implicated in normal embryonic development and disease.

Development of antiangiogenic therapies would be significantly facilitated by quantitative surrogate pharmacodynamic markers. Circulating peripheral blood endothelial cells (CECs) and/or their putative progenitor subset (CEPs) have been proposed but not yet fully validated for this purpose. Herein, we provide such validation by showing a striking correlation between highly genetically heterogeneous bFGF- or VEGF-induced angiogenesis and intrinsic CEC or CEP levels measured by flow cytometry, among eight different inbred mouse strains. Moreover, studies using genetically altered mice showed that levels of these cells are affected by regulators of angiogenesis, including VEGF, Tie-2, and thrombospondin-1. Finally, treatment with a targeted VEGFR-2 antibody caused a dose-dependent reduction in viable CEPs that precisely paralleled its previously and empirically determined antitumor activity.