Actin dynamics are required for proper cilia spacing, global coordination of cilia polarity, and coordination of metachronic cilia beating, whereas cytoplasmic microtubule dynamics are required for local coordination of polarity between neighboring cilia.

Planar cell polarity (PCP) is a property of epithelial tissues where cellular structures coordinately orient along a two-dimensional plane lying orthogonal to the axis of apical-basal polarity. PCP is particularly striking in tissues where multiciliate cells generate a directed fluid flow, as seen, for example, in the ciliated epithelia lining the respiratory airways or the ventricles of the brain. To produce directed flow, ciliated cells orient along a common planar axis in a direction set by tissue patterning, but how this is achieved in any ciliated epithelium is unknown. Here, we show that the planar orientation of Xenopus multiciliate cells is disrupted when components in the PCP-signaling pathway are altered non-cell-autonomously. We also show that wild-type ciliated cells located at a mutant clone border reorient toward cells with low Vangl2 or high Frizzled activity and away from those with high Vangl2 activity. These results indicate that the PCP pathway provides directional non-cell-autonomous cues to orient ciliated cells as they differentiate, thus playing a critical role in establishing directed ciliary flow.

We have used a 100 000 frame-per-second video to analyze the pinch-off of nitrogen gas bubbles in fluids with a wide range of viscosity. If the external fluid is highly viscous (eta(ext)>100 cP), the bubble neck radius is proportional to the time before break, tau, and decreases smoothly to zero. If the external fluid has low viscosity (eta(ext)<10 cP), the radius scales as tau(1/2) until an instability develops in the gas bubble, which causes the neck to rupture and tear apart. Finally, if the viscosity of the external fluid is in an intermediate range, an elongated thread is formed, which breaks apart into micron-sized bubbles.

We have studied the adsorption of 4 He on cesium in the temperature range from 1.3 to 4.1 K. The 4 He film undergoes a first-order phase transition known as prewetting. The prewetting line intersects the coexistence curve at the wetting temperature, 7^** 1.95 K, and terminates at 7^-2.5. K, the prewetting critical point. There are dramatic hysteresis effects when the temperature of the system is varied at coexistence in the vicinity of T w . This is the first experimental realization of a complete prewetting phase diagram.PACS numbers: 67.70.+n, 68.45.Gd On weak binding substrates, the interaction of an adatom with the surface can become comparable to the interaction of the adatoms with each other, and subtle free energy tradeoffs have large qualitative effects on the growth [1-5] and properties [6,7] of an adsorbed film. If, for example, a coexisting liquid and vapor are placed in a container at low temperature with sufficiently weakly binding walls, the walls will typically be covered with a fluid film that is only a few monolayers thick, i.e., they will be nonwet. As the temperature is raised, the energetic cost of forming a liquid-vapor interface (the liquidvapor surface tension) decreases, while the entropy of the film increases. Calculations [8][9][10] show that for many model systems the free energy of the film becomes equal to that of the bulk liquid at a characteristic temperature 7" w , the wetting temperature. For T >: 7 W , a macroscopically thick film wets the walls at coexistence. The phase transition between nonwet and wet walls can be either continuous or first order. If the transition is first order, with a discontinuous jump in the film thickness on the coexistence curve, thermodynamics requires that a phase boundary extend smoothly into the region of unsaturated films with n < /icoex-The phase boundary which separates regions of thick and thin films is known as the prewetting line, and is expected to terminate at a prewetting critical point. Although the prewetting line is a generic feature of a first-order wetting transition and its existence was first predicted 15 years ago [11], it has not been previously observed.Cheng, Cole, Saam, and Treiner (CCST) [1] have recently shown that the interaction of helium with substrates made of alkali metals is more than an order of magnitude weaker than with conventional substrates such as graphite. They also suggested that the phenomena of nonwetting and prewetting might be observable in these systems. Their calculations stimulated a number of experimental investigations [2-5] which have shown that adsorption on these substrates is highly anomalous. In this paper we present measurements of the complete wetting phase diagram for helium on cesium. We show that a first-order wetting transition occurs on the coexistence curve at 7^ = 1.95 K. Isotherms above T w show an abrupt step in the film thickness at pressures below the saturated vapor pressure characteristic of prewetting. Below T Wi there are large hysteresis effects and the film thickness of coexisten...

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