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6. Zelhof, A.C., Hardy, R.W., Becker, A., and matrix on tissue deformation. Philos. Transact. activates ezrin/radixin/moesin (ERM) proteins: Zuker, C.S. (2006). Transforming the A Math. Phys. Eng. Sci. 364, 1407–1422. activation mechanisms and physiological architecture of compound eyes. Nature 443, 12. Felix, C.F., Moreira, C.C., Oliveira, M.S., implications. Am. J. Physiol. Cell. Physiol. 294, 696–699. Sola-Penna, M., Meyer-Fernandes, J.R., C197–C212. 7. Johnson, K., Grawe, F., Grzeschik, N., and Scofano, H.M., and Ferreira-Pereira, A. (1999). 15. Kunda, P., Pelling, A.E., Liu, T., and Baum, B. Knust, E. (2002). Drosophila crumbs is required Protection against thermal denaturation by (2008). Moesin controls cortical rigidity, cell to inhibit light-induced photoreceptor trehalose on the plasma membrane H+-ATPase rounding, and spindle morphogenesis during degeneration. Curr. Biol. 12, 1675–1680. from yeast. Synergetic effect between mitosis. Curr. Biol. 18, 91–101. 8. Osorio, D. (2007). Spam and the evolution of trehalose and phospholipid environment. the fly’s eye. BioEssays 29, 111–115. Eur. J. Biochem. 266, 660–664. 9. Kiger, A.A., Baum, B., Jones, S., Jones, M.R., 13. Hill, W.G., Kaetzel, M.A., Kishore, B.K., MRC Laboratory for Molecular Cell Biology, Coulson, A., Echeverri, C., and Perrimon, N. Dedman, J.R., and Zeidel, M.L. (2003). and the Department of Cell and (2003). A functional genomic analysis of cell Annexin A4 reduces water and proton Developmental Biology, UCL, Gower Street, morphology using RNA interference. permeability of model membranes but does London, UK. J. Biol. 2, 27. not alter aquaporin 2-mediated water transport 10. Hohmann, S., Krantz, M., and Nordlander, B. in isolated endosomes. J. Gen. Physiol. 121, E-mail: [email protected], [email protected], (2007). Yeast osmoregulation. Methods 413–425. [email protected] Enzymol. 428, 29–45. 14. Rasmussen, M., Alexander, R.T., Darborg, B.V., 11. Lu, Y., Parker, K.H., and Wang, W. (2006). Mobjerg, N., Hoffmann, E.K., Kapus, A., and Effects of osmotic pressure in the extracellular Pedersen, S.F. (2008). Osmotic cell shrinkage DOI: 10.1016/j.cub.2008.04.032

Insect Migration: Do Migrant Moths migrants have been assumed to hitch a ride in both directions on winds that Know Where They Are Heading? are usually seasonally ‘favorable’. The silver Y moth, Autographa gamma (Figure 1), migrates in Moth migration has been assumed to involve hitching a ride in favorable winds. autumn from northern Europe to A new study has shown that silver Y moths migrate only on nights when winds North Africa and the Mediterranean would displace them southward, implying that they detect their direction of basin; in spring its descendants movement while airborne, likely by a magnetic sense. re-migrate northward. In a recent report in Current Biology [8], the Ring T. Carde´ Migration thus need not involve vertical-looking radar (VLR) technique return trips by the same individuals, [9] was coupled with meteorological Migration is a persistent, nor does a migrant need to direct its data to provide new insights into how straightened-out movement that takes track [4], as the monarch does; in this noctuid moth heads toward its an organism from a habitat lacking small insects, like aphids, migration is overwintering habitat, in this case en a resource to another, more favorable subject to the vagaries of the route over central England toward location. During migration, the prevailing wind. While much debate the Mediterranean basin. What is organism’s ‘vegetative’ behaviors remains on the proximate unique in this study is the such as feeding and reproduction are mechanisms governing these mass simultaneous measurement by VLR temporarily suppressed [1]. In insects, movements, the ultimate selective of the body orientation and track the distances traveled can exceed force explaining these displacements directions of numerous individual 3,000 km, as in the case of monarch is spread of reproductive efforts in moths on many evenings and the butterflies, Danaus plexippus, flying in time and space [5]. availability of wind movement data at autumn from New England to their Many noctuid moths migrate in relevant altitudes. overwintering home in the Sierra spring from mild-weather temperate In autumn, mass migratory flights Madre Mountains in Mexico. This regions to exploit higher latitude occur on those nights when the wind butterfly migrates in daytime, and regions in summer. Migration to high flow is favorable for rapid southward usually near ground level. Using latitudes has been likened to a Pied movement and moths are concentrated a novel tethering system to simulate Piper effect, leading migrants to at altitudes that maximize their free flight, the monarch’s only exploit a temporarily favorable displacement. VLR pinpoints the body orientation mechanism verified so far environment, but without the prospect orientation of individual moths as they is a sun compass; earlier evidence that of their progeny surviving the winter pass hundreds of meters overhead, the monarch uses magnetic cues or [6]. The question of whether the and thereby can indicate whether they polarized light in navigation has been descendants of wind-borne migrant are contributing to their downwind discounted [2,3]. Migration can also be moths have a return migration in displacement by heading with the wind. a relatively local phenomenon, on the autumn to lower latitudes has been The silver Y does not use changes at order of a kilometer or less, as with the debated, but there is now evidence in ground level in temperature, humidity, seasonal movement of the black bean some species from mark-release- wind speed, wind direction or aphid, Aphis fabae, which has two recapture experiments — in which barometric pressure to forecast generations on a woody host before a many moths are marked and a very a directionally favorable wind springtime flight that takes it into bean few are recovered at considerable above — indeed, in autumn the wind fields where it reproduces asexually distances from their release direction at migratory height was found until fall, when sexual, winged forms point — that such to and fro migration to be randomly distributed and nights return to the woody host [4]. can occur (for example [7]). Such with a southerly wind flow at migratory Dispatch R473 altitudes were not correlated with any obvious meteorological cues at ground level [8]. This indicates that moths have a mechanism for determining their direction of displacement while they are airborne and then deciding whether to migrate. If on a given night the wind is blowing in the ‘wrong’ direction, they presumably descend to ground level and do not migrate. The silver Y must detect an unfavorable displacement — net movement away from the favored direction — by sensing that the flow of the visual field below is not advancing front-to-rear. By heading with the wind, the silver Y can add about 5 m sec21 in their airspeed to a southerly movement, with a potential overall nightly migration of up to 650 km. Moreover, when the wind is generally but not precisely Figure 1. The silver Y moth, Autographa gamma. (Photograph courtesy of Ian Woiwod.) (more than 20) aligned with the favored migratory direction, moths can migrate more than 100 km in during the dry season, the African adjust their trajectory to compensate a single evening’s flight, transported armyworm moth, Spodoptera for wind-induced, sideways drift, by an advancing weather front. Such exempta, is carried downwind, the providing further evidence that they displacements from outbreak direction toward the Inter-Tropical can sense their direction of populations can exceed aerial Convergence Zone, where convergent movement and actively direct their densities of 10,000 moths over winds are likely to produce rain and path. Although the compass a hectare, with moths cruising at to concentrate moth density [18]. mechanism remains to be established, altitudes of hundreds of meters. Similarly, the movement of Spodoptera a magnetic sense appears to be the These flights were among the first frugiperda in Central America may be only plausible explanation. insect mass migrations to be a strategy to locate areas of recent There is experimental evidence of monitored by radar [16], and in this rain and therefore to elevate the a magnetic sense in flies, beetles, case the moths were observed to prospect of finding a host [19]. It has ants, bees and termites [10]. orientate directly downwind (when been assumed that these moths take Experiments with a four-armed choice wind direction veered with height so flight and allow themselves to be chamber with two migratory noctuids did the orientation). The exodus carries transported downwind, trading in most in normal and reversed artificial males and females out of defoliated cases an unfavorable habitat for magnetic fields suggested forests to a new habitat. Because the a favorable one. a geomagnetic effect on the moths’ fir-spruce forests dominate the region, New findings generate new cardinal settling position at evening’s as morning approaches moths often questions. How does the supposed end [11,12], but the endpoint settle in exploitable forests, although compass system work? Do springtime measurement of this assay is far the destination also can be unfavorable movements of the silver Y moth have removed from the orientation of freely habitats and even open ocean. a directed heading northward, or do flying moths. Although the role of Essentially all migrating females have moths simply hitch a ride on winds a magnetic sense in monarch migration already mated, usually once, and many that are on average directionally remains speculative [3], the direction re-mate after migration. Similarly, ‘favorable’? If seasonal movement of initial departure of released migrants mated female gypsy moths, Lymantria northward by the silver Y in the spring is [13] can be disrupted by prior dispar, in central Siberia migrate up to also guided by a sense of direction, exposure to a strong magnetic field. 100 km. This lymantrid moth flies in how is this reversal of orientation Similarly, the direction of a neotropical a random direction within meters of the orchestrated? Do other migrant pierid butterfly’s migration also is ground, evidently not influenced by noctuids use a similar orientation shifted by prior exposure to a strong synoptic wind flow [17]. In these two mechanism — indeed, is this magnetic field [14]. A strong magnetic species, the moths do not direct their specialized form of orientation during field, however, may have a disruptive displacement toward a known migration found in other moth and effect on other compass mechanisms direction. insect lineages? What is clear from the or on general physiology [15]. Long-distance migration in moths, new study [8] is that the silver Y moth Migration, often termed ‘dispersal’, however, is most prevalent among has a sophisticated system of compass is known in other moth lineages. noctuids. Some movement patterns navigation, presumably magnetically The tortricid spruce budworm, appear to maximize the discovery of based, that ensures that its autumn (Christoneura fumiferana), a defoliator short-lived, dispersed and migration is not subject to the vagaries of fir-spruce forests in eastern Canada, unpredictable habitats. For example, of the wind. Current Biology Vol 18 No 11 R474

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ER Biogenesis: Self-Assembly of Unlike the ‘classical’ curvature scaffolds, such as coat proteins, that Tubular Topology by Protein Hairpins densely cover the membrane, just a small fraction of reticulons and DP1/Yop1p proteins in a membrane is The structure of the endoplasmic reticulum (ER) depends on members of the sufficient to maintain the curvature of reticulon and DP1/Yop1p families. Two of these proteins are sufficient to form the ER tubules [5]. Thus plenty of the tubular membrane networks from pure phospholipid vesicles, thus revealing membrane surface remains accessible a new paradigm of ER morphogenesis. from the cytoplasm, a feature critical for ER functionality. Another important Anna Shnyrova, Vadim A. Frolov actively involved in ER biogenesis [3]. characteristic of this new type of and Joshua Zimmerberg* Members of these families were first curvature machinery is its stable found to play a critical role in the association with the membrane. The endoplasmic reticulum (ER) is process of in vitro formation of DP1/Yop1p and reticulons are integral an extremely dynamic membrane tubular networks from microsomes of membrane proteins [5], thus their organelle consisting of interconnecting Xenopus oocytes [4,6]. Furthermore, curvature activity is not based on tubules and sheets that are deeply simultaneous knock-out of Yop1p the traditional pathway of the involved in various signaling and and reticulons led to the disappearance classical curvature scaffolds [7,8], transport processes in cells [1–3]. of tubular ER in Saccharomyces where the binding of these proteins ER tubules are arranged in conduits cerevisiae [4], thus confirming the to the membrane precedes protein spanning the entire cytoplasm. The key role of these proteins in the ER self-assembly. Likewise, these proteins structural stability of this tubular formation. In the recent study, Hu are not removed from the membrane network must be combined with the and co-authors [5] revealed that upon the completion of membrane high plasticity of tubule membranes Yop1p and Rtn1p proteins are not shape transformation. Thus, their required for ER functionality [3]; only required but also sufficient to form action is revealed more in the maintaining ER shape is therefore an ER-like tubular membrane network evolution of a membrane subsystem a challenging task. However, recent from pure phospholipid membranes than in a localized membrane findings reveal that tubular membrane [5]. These findings establish the role deformation. networks can be organized by of Yop1p and Rtn1p as key regulators To understand the modus operandi a single protein species — either Yop1p of the ER morphology, encoding and of these proteins in detail, it is or Rtn1p proteins — isolated from the supporting the curvature of the ER instructive to follow step-by-step the ER membrane [4,5]. tubules. in vitro reaction that results in the Yop1p and Rtn1p proteins belong The functionality of these proteins self-assembly of ER-like structures to DP1/Yop1p and reticulon protein is based on their specific molecular from proteolipid vesicles containing families, respectively, which are design and interaction patterns. Yop1p and Rtn1p proteins. The small