- Email: [email protected]
Centriole Assembly: The Origin of Nine-ness
Dispatch R1057
a hereditary component [13]. Thus even quite large differences between small groups of animals may be accidental. The results of Farley et al. [1] suggest two particular conclusions. First, it has always seemed possible that the mechanics of dimension reduction models might have little to do with real visual cortex development, even though the models predict the end result of it well enough. Thus, prenatal development — as optimised by evolution — might have contrived to come up with columnar arrangements that satisfy completeness and continuity constraints, without optimising them explicitly, or being able to adaptively optimize them in the face of perturbations. Farley et al.’s [1] results suggest the opposite and that developmental mechanisms act, like the models, to adaptively optimize coverage at the expense of continuity. Second, because eye removal was performed before thalamic inputs had arrived at the cortex, and most likely before any kind of columnar structures, or precursors of them, would have been present, it could plausibly have resulted in a remodelling of the entire system of columns, not just a sculpting of a pre-existing pattern. This would further support the view of developing cortex as a plastic, self-organizing system, relatively independent of genetic control. This is not an inescapable conclusion however. Removal of an eye might alter chemical, or genetically mediated cues, in
addition to neural activity. A change in pattern periodicity might at first sight imply a wholescale remodelling of columnar structures, but in fact changes of the magnitude seen by Farley et al. [1] (around 10%) can be accomplished by relatively small alterations in structural detail. Figure 2 shows how this can be so. If these experiments do not conclusively resolve the issue of the innate determination of columnar structures, what kinds of experiments might? Comparison of the patterns of gene expression in different columns might give clues and is now technically feasible, although changes in gene expression could be linked to changes in neural activity, making the two hard to disentangle. A more decisive test would be to compare columnar patterns in cloned animals. If these turned out to be different (as are coat patterns [14]), it would strongly support the self-organizing view of columnar development. But while the answers to these questions remain unknown, visual cortex modellers can, for the moment, chalk up another success. References 1. Farley, B.J., Yu, H., Jin, D.Z., and Sur, M. (2007). Alteration of visual input results in a coordinated reorganization of multiple visual cortex maps. J. Neurosci. 27, 10299–10310. 2. Wiesel, T.N., and Hubel, D.H. (1963). Single-cell responses in striate cortex of kittens deprived of vision in one eye. J. Neurophysiol. 26, 1003–1017. 3. Hubel, D.H., Wiesel, T.N., and LeVay, S. (1977). Plasticity of ocular dominance columns in monkey striate cortex. Phil. Trans. R. Soc. Lond. B. 278, 131–163.
Centriole Assembly: The Origin of Nine-ness Recent studies of the Chlamydomonas bld10 mutant have revealed that the ninefold symmetry of the centriole is set by the length of the cartwheel spokes, which fixes the diameter, and thereby the circumference, of the centriole. Wallace F. Marshall The centriole is a cylindrical structure found in the core of the centrosome. Centrioles possess
a remarkable ninefold symmetry, consisting of nine parallel microtubule triplets arranged like the blades of a turbine. At the proximal end of the centriole,
4. Wiesel, T.N., and Hubel, D.H. (1974). Ordered arrangement of orientation columns in monkeys lacking visual experience. J. Comp. Neurol. 158, 307–318. 5. Horton, J.C., and Hocking, D.R. (1996). An adult-like pattern of ocular dominance columns in striate cortex of newborn monkeys prior to visual experience. J. Neurosci. 16, 1791–1807. 6. Crair, M.C., Gillespie, D.C., and Stryker, M.P. (1998). The role of visual experience in the development of columns in cat visual cortex. Science 279, 566–570. 7. Wong, R.O. (1999). Retinal waves and visual system development. Annu. Rev. Neurosci. 22, 29–47. 8. Goodhill, G.J. (2007). Contributions of theoretical modelling to the understanding of neural map development. Neuron 56, 301–311. 9. Durbin, R., and Mitchison, G.J. (1990). A dimension reduction framework for understanding cortical maps. Nature 343, 644–647. 10. Swindale, N.V. (2004). How different feature spaces may be represented in visual cortex. Network 15, 217–242. 11. Carreira-Perpin˜a´n, M.A., Lister, R., and Goodhill, G.J. (2005). A computational model for the development of multiple maps in primary visual cortex. Cerebral Cortex 15, 1222–1233. 12. Horton, J.C., and Hocking, D.R. (1996). Intrinsic variability of ocular dominance column periodicity in normal macaque monkeys. J. Neurosci. 16, 7228–7239. 13. Kaschube, M., Wolf, F., Puhlmann, M., Rathjen, S., Schmidt, K.-F., Geisel, T., and Lo¨wel, S. (2003). The pattern of ocular dominance columns in cat primary visual cortex: intra- and interindividual variability of column spacing and its dependence on genetic background. Eur. J. Neurosci. 18, 3251–3266. 14. Shin, T., Kraemer, D., Pryor, J., Liu, L., Rugila, R., Howe, L., Buck, S., Murphy, K., Lyons, L., and Westhusin, M. (2002). A cat cloned by nuclear transplantation. Nature 415, 859.
Department of Ophthalmology and Visual Sciences, University of British Columbia, 2550 Willow St., Vancouver, V5Z 3N9, British Columbia, Canada. E-mail: [email protected] DOI: 10.1016/j.cub.2007.10.030
where the minus-ends of the microtubule blades are located, is a structure called the ‘cartwheel’ consisting of a central hub joined to the blades by nine spokes. So, how does the ninefold symmetry of the centriole arise? One possible model is that assembly is templated from a single molecule or complex that is located in the cartwheel hub and itself has a ninefold symmetrical repeat structure. This central template would then produce an
Current Biology Vol 17 No 24 R1058
Figure 1. Testing the central-template model versus the blade-packing model. The central-template model predicts that a gap will result from the removal of one subunit, with the remaining subunits staying in their normal places. The blade-packing model predicts that removal of one subunit would lead to the formation of a smaller centriole with eight subunits arranged around a smaller circumference.
Removal of one subunit
8-fold symmetry
9-fold symmetry with gap
Blade-packing model
Central-template model Current Biology
array of spokes protruding at appropriate angles to give the overall symmetry to the organelle. The fundamental structure of a helices allows for repeats with ninefold rotational symmetry and has therefore been proposed as the origin of symmetry in centrioles [1]. Another version of the central-template model proposes a central core with nine microtubule docking sites [2]. Both forms of the central-template model posit some template structure with ninefold symmetry. The alternative model is that the ninefold symmetry arises from packing interactions between the triplet blade-containing subunits which set the size of the centriole by fitting together like slices of a pie [3]. In this type of model, the number of triplets around the rim of the centriole, and hence the degree of symmetry, is determined simply by the number of triplet subunits that can be packed within the circumference of the centriole. Although more complex models can of course be imagined, here I will focus on these two simple models. The simplest way to distinguish between the central-templating and blade-packing models is to reduce the number of blades from nine down to eight, and then ask whether the angular relationship between adjacent blades is changed (Figure 1). The blade-packing
model predicts that if a piece of the pie is missing, the remaining pieces would redistribute themselves evenly to yield an eightfold symmetrical arrangement. The central-template model predicts that a gap would form, with the eight remaining subunits keeping their normal positions. A genetic test of these models based on missing blades requires a mutant in which the number of blades is reduced. The ideal mutant would satisfy two criteria. The first criterion is that the missing blades must be missing all along their lengths, and not simply truncated. If one or more blades are shorter than the others, this might produce a gap in some cross sections but the remaining short blade at one end could still maintain normal packing interactions leading to ninefold symmetry. Such a mutant would therefore not be informative. A second criterion is that the mutation should not be in a gene encoding a centrally located protein. If there is some protein with an intrinsic ninefold symmetry resulting from, for example, nine repeat subunits, a mutation that deleted one of the nine repeats might produce eightfold symmetry. We now review several experiments in which blade number is altered. Chlamydomonas delta and epsilon tubulin mutations in
which the number of microtubules in a blade is reduced from three down to two or one do not result in a change in symmetry [4], but this does not necessarily rule out the blade-packing model since the microtubules probably do not determine the effective width of the blade unit. An extragenic suppressor of an epsilon tubulin allele forms centrioles with fewer than nine blades in some cross sections, and in this case a clear gap was seen with the remaining triplets arranged according to the normal ninefold symmetry [5]. However, analysis of adjacent sections showed that the blades corresponding to the gaps were not actually missing, but merely truncated, so that at the distal end there were still nine blades present [5]. This type of mutant therefore fails to meet our first criterion. In Drosophila primary spermatocytes defective in the centriole protein SAS-6, centrioles were observed that contained fewer than nine triplets [3]. Importantly, these centrioles with reduced numbers of blade units had a reduced diameter, which is consistent with the blade-packing model. However, the remaining blades were not symmetrically arranged, showing pronounced gaps in the structure, so the results do not exactly match the predictions of the blade-packing model. Although the presence of gaps fits the prediction of the central-templating model, the angles between the remaining blades were not consistent with a normal ninefold symmetry, so the results do not exactly match the central-templating model either. Besides, as SAS-6 is thought to form a tube corresponding to the cartwheel hub [6], SAS-6 mutations fail to meet our second criterion as discussed above. A new study has finally presented a clear result based on a mutant that alters blade number and satisfies our two criteria outlined above. Null alleles of the Chlamydomonas gene BLD10 lack centrioles [7]. The BLD10 protein is a coiled-coil protein localizing to the cartwheel spoke pinhead, which is the portion of the spoke that attaches to the microtubule blades. The key to
Dispatch R1059
testing the two models came from constructing truncated BLD10 alleles predicted to make shorter coiled coils. Expressing these truncated proteins in the bld10 null mutant background led to production of structurally abnormal centrioles in which the number of triplet blades was reduced [8]. Centrioles with eight blades had a reduced diameter with the remaining eight blades arranged in an eightfold symmetric arrangement. The construct affected the blades along their entire length, and was due to mutation in a protein that does not localize to the central hub but rather to a structure associated with the blades themselves, thus the study satisfies both of our criteria defined above for a useful mutation. The result thus suggests that the normal ninefold symmetry of the centriole does not arise from an underlying symmetry in the cartwheel hub. How then does BLD10 determine centriole symmetry? Significantly, many of the abnormal centrioles show an abnormally short cartwheel spoke length and
a reduced diameter. Since the circumference of a circle is proportional to its diameter, a reduction in diameter by 1/9 would reduce the circumference by 1/9, corresponding to loss of one triplet. Thus it appears that the symmetry of the centriole is ultimately set by the diameter of the centriole, which is in turn set by the length of the cartwheel spokes [8]. The shorter spokes produced by truncated BLD10 set the diameter to a smaller value, so that only eight triplets can now be accommodated. This study provides an interesting geometrical mechanism by which a length can control a number. Understanding centriole assembly is likely to reveal many more engineering-design principles that cells use to build complex structures.
1. Satir, P., and Satir, B. (1964). A model for ninefold symmetry in a keratin and cilia. J. Theor. Biol. 7, 123–128. 2. Albrecht-Buehler, G. (1990). The iris diaphragm model of centriole and basal body formation. Cell Motil. Cytoskel. 17, 197–213. 3. Rodrigues-Martins, A., BettencourtDias, M., Riparbelli, M., Ferreira, C.,
Cuttlefish are masters of disguise, rapidly changing colour to blend with their backgrounds. A new study shows that they break camouflage to direct warning messages at certain predators, but only those likely to be dissuaded by visual signals.
The study of anti-predator signals has proven to be a rich hunting ground for evolutionary biologists and cognitive psychologists. Empirical support for a number of classical evolutionary processes, such as kin-selected altruism, aposematism and mimicry, has come from studies of the signals made by prey to potential predators [1]. Perhaps even more striking, the use of different signals for different threats, and their apparently deceptive use for social manipulation, provide tantalising glimpses of the origins of language
5.
6.
7.
8.
References
Animal Behaviour: Strategic Signalling by Cephalopods
Innes C. Cuthill
4.
Ferreira, I., Callaini, G., and Glover, D.M. (2007). DSAS-6 organizes a tube-like centriole precursor, and its absence suggests modularity in centriole assembly. Curr. Biol. 17, 1465–1472. O’Toole, E.T., Giddings, T.H., McIntosh, J.R., and Dutcher, S.K. (2003). Three-dimensional organization of basal bodies from wild-type and delta-tubulin deletion strains of Chlamydomonas reinhardtii. Mol. Biol. Cell 14, 2999–3012. Preble, A.M., Giddings, T.H., and Dutcher, S.K. (2001). Extragenic bypass suppressors of mutations in the essential gene BLD2 promote assembly of basal bodies with abnormal microtubules in Chlamydomonas reinhardtii. Genetics 157, 163–181. Pelletier, L., O’Toole, E., ASchwager, A., Hyman, A.A., and Muller-Reichert, T. (2006). Centriole assembly in Caenorhabditis elegans. Nature 444, 619–623. Matsuura, K., Lefebvre, P.A., Kamiya, R., and Hirono, M. (2004). Bld10p, a novel protein essential for basal body assembly in Chlamydomonas: localization to the cartwheel, the first ninefold symmetrical structure appearing during assembly. J. Cell Biol. 165, 663–671. Hiraki, M., Nakazawa, Y., Kamiya, R., and Hirono, M. (2007). Bld10p constitutes the cartwheel-spoke tip and stabilizes the 9-fold symmetry of the centriole. Curr. Biol. 17, 1778–1783.
and of a ‘Theory of Mind’ (where one individual interprets the behaviour of another in terms of some model of the latter’s intentions or knowledge) [2]. The classic example of strategic anti-predator signalling comes from vervet monkeys’ use of different alarm calls for different predators [3], but instances of the use of different signals for different threats have now been substantiated in a number of vertebrates (see references in [4]). A new experimental study by Keri Langridge and colleagues [4], reported in this issue of Current Biology, adds a new and important
Department of Biochemistry and Biophysics, University of California-San Francisco, 600 16th St., San Francisco, California, USA. E-mail: [email protected] DOI: 10.1016/j.cub.2007.10.038
twist to the field of anti-predator signalling. Not only does it concern a cephalopod mollusc, adding weight to the view that these invertebrates can match many vertebrates in their cognitive and behavioural complexity, but it provides the first clear example of strategic choice with respect to the likely effectiveness of different signals against specific predators. Cuttlefish, like their relatives squid and octopus, have excellent vision and skin pigmentation (and texture) that is under direct and rapid neural control [5]. These attributes allow them unparalleled dynamic camouflage [6], combining general background resemblance, disruptive patterns and posture to achieve near-invisibility in a couple of seconds. But in the face of predators using tactile, olfactory or electromagnetic cues, visual deception may fail and here,
a hereditary component [13]. Thus even quite large differences between small groups of animals may be accidental. The results of Farley et al. [1] suggest two particular conclusions. First, it has always seemed possible that the mechanics of dimension reduction models might have little to do with real visual cortex development, even though the models predict the end result of it well enough. Thus, prenatal development — as optimised by evolution — might have contrived to come up with columnar arrangements that satisfy completeness and continuity constraints, without optimising them explicitly, or being able to adaptively optimize them in the face of perturbations. Farley et al.’s [1] results suggest the opposite and that developmental mechanisms act, like the models, to adaptively optimize coverage at the expense of continuity. Second, because eye removal was performed before thalamic inputs had arrived at the cortex, and most likely before any kind of columnar structures, or precursors of them, would have been present, it could plausibly have resulted in a remodelling of the entire system of columns, not just a sculpting of a pre-existing pattern. This would further support the view of developing cortex as a plastic, self-organizing system, relatively independent of genetic control. This is not an inescapable conclusion however. Removal of an eye might alter chemical, or genetically mediated cues, in
addition to neural activity. A change in pattern periodicity might at first sight imply a wholescale remodelling of columnar structures, but in fact changes of the magnitude seen by Farley et al. [1] (around 10%) can be accomplished by relatively small alterations in structural detail. Figure 2 shows how this can be so. If these experiments do not conclusively resolve the issue of the innate determination of columnar structures, what kinds of experiments might? Comparison of the patterns of gene expression in different columns might give clues and is now technically feasible, although changes in gene expression could be linked to changes in neural activity, making the two hard to disentangle. A more decisive test would be to compare columnar patterns in cloned animals. If these turned out to be different (as are coat patterns [14]), it would strongly support the self-organizing view of columnar development. But while the answers to these questions remain unknown, visual cortex modellers can, for the moment, chalk up another success. References 1. Farley, B.J., Yu, H., Jin, D.Z., and Sur, M. (2007). Alteration of visual input results in a coordinated reorganization of multiple visual cortex maps. J. Neurosci. 27, 10299–10310. 2. Wiesel, T.N., and Hubel, D.H. (1963). Single-cell responses in striate cortex of kittens deprived of vision in one eye. J. Neurophysiol. 26, 1003–1017. 3. Hubel, D.H., Wiesel, T.N., and LeVay, S. (1977). Plasticity of ocular dominance columns in monkey striate cortex. Phil. Trans. R. Soc. Lond. B. 278, 131–163.
Centriole Assembly: The Origin of Nine-ness Recent studies of the Chlamydomonas bld10 mutant have revealed that the ninefold symmetry of the centriole is set by the length of the cartwheel spokes, which fixes the diameter, and thereby the circumference, of the centriole. Wallace F. Marshall The centriole is a cylindrical structure found in the core of the centrosome. Centrioles possess
a remarkable ninefold symmetry, consisting of nine parallel microtubule triplets arranged like the blades of a turbine. At the proximal end of the centriole,
4. Wiesel, T.N., and Hubel, D.H. (1974). Ordered arrangement of orientation columns in monkeys lacking visual experience. J. Comp. Neurol. 158, 307–318. 5. Horton, J.C., and Hocking, D.R. (1996). An adult-like pattern of ocular dominance columns in striate cortex of newborn monkeys prior to visual experience. J. Neurosci. 16, 1791–1807. 6. Crair, M.C., Gillespie, D.C., and Stryker, M.P. (1998). The role of visual experience in the development of columns in cat visual cortex. Science 279, 566–570. 7. Wong, R.O. (1999). Retinal waves and visual system development. Annu. Rev. Neurosci. 22, 29–47. 8. Goodhill, G.J. (2007). Contributions of theoretical modelling to the understanding of neural map development. Neuron 56, 301–311. 9. Durbin, R., and Mitchison, G.J. (1990). A dimension reduction framework for understanding cortical maps. Nature 343, 644–647. 10. Swindale, N.V. (2004). How different feature spaces may be represented in visual cortex. Network 15, 217–242. 11. Carreira-Perpin˜a´n, M.A., Lister, R., and Goodhill, G.J. (2005). A computational model for the development of multiple maps in primary visual cortex. Cerebral Cortex 15, 1222–1233. 12. Horton, J.C., and Hocking, D.R. (1996). Intrinsic variability of ocular dominance column periodicity in normal macaque monkeys. J. Neurosci. 16, 7228–7239. 13. Kaschube, M., Wolf, F., Puhlmann, M., Rathjen, S., Schmidt, K.-F., Geisel, T., and Lo¨wel, S. (2003). The pattern of ocular dominance columns in cat primary visual cortex: intra- and interindividual variability of column spacing and its dependence on genetic background. Eur. J. Neurosci. 18, 3251–3266. 14. Shin, T., Kraemer, D., Pryor, J., Liu, L., Rugila, R., Howe, L., Buck, S., Murphy, K., Lyons, L., and Westhusin, M. (2002). A cat cloned by nuclear transplantation. Nature 415, 859.
Department of Ophthalmology and Visual Sciences, University of British Columbia, 2550 Willow St., Vancouver, V5Z 3N9, British Columbia, Canada. E-mail: [email protected] DOI: 10.1016/j.cub.2007.10.030
where the minus-ends of the microtubule blades are located, is a structure called the ‘cartwheel’ consisting of a central hub joined to the blades by nine spokes. So, how does the ninefold symmetry of the centriole arise? One possible model is that assembly is templated from a single molecule or complex that is located in the cartwheel hub and itself has a ninefold symmetrical repeat structure. This central template would then produce an
Current Biology Vol 17 No 24 R1058
Figure 1. Testing the central-template model versus the blade-packing model. The central-template model predicts that a gap will result from the removal of one subunit, with the remaining subunits staying in their normal places. The blade-packing model predicts that removal of one subunit would lead to the formation of a smaller centriole with eight subunits arranged around a smaller circumference.
Removal of one subunit
8-fold symmetry
9-fold symmetry with gap
Blade-packing model
Central-template model Current Biology
array of spokes protruding at appropriate angles to give the overall symmetry to the organelle. The fundamental structure of a helices allows for repeats with ninefold rotational symmetry and has therefore been proposed as the origin of symmetry in centrioles [1]. Another version of the central-template model proposes a central core with nine microtubule docking sites [2]. Both forms of the central-template model posit some template structure with ninefold symmetry. The alternative model is that the ninefold symmetry arises from packing interactions between the triplet blade-containing subunits which set the size of the centriole by fitting together like slices of a pie [3]. In this type of model, the number of triplets around the rim of the centriole, and hence the degree of symmetry, is determined simply by the number of triplet subunits that can be packed within the circumference of the centriole. Although more complex models can of course be imagined, here I will focus on these two simple models. The simplest way to distinguish between the central-templating and blade-packing models is to reduce the number of blades from nine down to eight, and then ask whether the angular relationship between adjacent blades is changed (Figure 1). The blade-packing
model predicts that if a piece of the pie is missing, the remaining pieces would redistribute themselves evenly to yield an eightfold symmetrical arrangement. The central-template model predicts that a gap would form, with the eight remaining subunits keeping their normal positions. A genetic test of these models based on missing blades requires a mutant in which the number of blades is reduced. The ideal mutant would satisfy two criteria. The first criterion is that the missing blades must be missing all along their lengths, and not simply truncated. If one or more blades are shorter than the others, this might produce a gap in some cross sections but the remaining short blade at one end could still maintain normal packing interactions leading to ninefold symmetry. Such a mutant would therefore not be informative. A second criterion is that the mutation should not be in a gene encoding a centrally located protein. If there is some protein with an intrinsic ninefold symmetry resulting from, for example, nine repeat subunits, a mutation that deleted one of the nine repeats might produce eightfold symmetry. We now review several experiments in which blade number is altered. Chlamydomonas delta and epsilon tubulin mutations in
which the number of microtubules in a blade is reduced from three down to two or one do not result in a change in symmetry [4], but this does not necessarily rule out the blade-packing model since the microtubules probably do not determine the effective width of the blade unit. An extragenic suppressor of an epsilon tubulin allele forms centrioles with fewer than nine blades in some cross sections, and in this case a clear gap was seen with the remaining triplets arranged according to the normal ninefold symmetry [5]. However, analysis of adjacent sections showed that the blades corresponding to the gaps were not actually missing, but merely truncated, so that at the distal end there were still nine blades present [5]. This type of mutant therefore fails to meet our first criterion. In Drosophila primary spermatocytes defective in the centriole protein SAS-6, centrioles were observed that contained fewer than nine triplets [3]. Importantly, these centrioles with reduced numbers of blade units had a reduced diameter, which is consistent with the blade-packing model. However, the remaining blades were not symmetrically arranged, showing pronounced gaps in the structure, so the results do not exactly match the predictions of the blade-packing model. Although the presence of gaps fits the prediction of the central-templating model, the angles between the remaining blades were not consistent with a normal ninefold symmetry, so the results do not exactly match the central-templating model either. Besides, as SAS-6 is thought to form a tube corresponding to the cartwheel hub [6], SAS-6 mutations fail to meet our second criterion as discussed above. A new study has finally presented a clear result based on a mutant that alters blade number and satisfies our two criteria outlined above. Null alleles of the Chlamydomonas gene BLD10 lack centrioles [7]. The BLD10 protein is a coiled-coil protein localizing to the cartwheel spoke pinhead, which is the portion of the spoke that attaches to the microtubule blades. The key to
Dispatch R1059
testing the two models came from constructing truncated BLD10 alleles predicted to make shorter coiled coils. Expressing these truncated proteins in the bld10 null mutant background led to production of structurally abnormal centrioles in which the number of triplet blades was reduced [8]. Centrioles with eight blades had a reduced diameter with the remaining eight blades arranged in an eightfold symmetric arrangement. The construct affected the blades along their entire length, and was due to mutation in a protein that does not localize to the central hub but rather to a structure associated with the blades themselves, thus the study satisfies both of our criteria defined above for a useful mutation. The result thus suggests that the normal ninefold symmetry of the centriole does not arise from an underlying symmetry in the cartwheel hub. How then does BLD10 determine centriole symmetry? Significantly, many of the abnormal centrioles show an abnormally short cartwheel spoke length and
a reduced diameter. Since the circumference of a circle is proportional to its diameter, a reduction in diameter by 1/9 would reduce the circumference by 1/9, corresponding to loss of one triplet. Thus it appears that the symmetry of the centriole is ultimately set by the diameter of the centriole, which is in turn set by the length of the cartwheel spokes [8]. The shorter spokes produced by truncated BLD10 set the diameter to a smaller value, so that only eight triplets can now be accommodated. This study provides an interesting geometrical mechanism by which a length can control a number. Understanding centriole assembly is likely to reveal many more engineering-design principles that cells use to build complex structures.
1. Satir, P., and Satir, B. (1964). A model for ninefold symmetry in a keratin and cilia. J. Theor. Biol. 7, 123–128. 2. Albrecht-Buehler, G. (1990). The iris diaphragm model of centriole and basal body formation. Cell Motil. Cytoskel. 17, 197–213. 3. Rodrigues-Martins, A., BettencourtDias, M., Riparbelli, M., Ferreira, C.,
Cuttlefish are masters of disguise, rapidly changing colour to blend with their backgrounds. A new study shows that they break camouflage to direct warning messages at certain predators, but only those likely to be dissuaded by visual signals.
The study of anti-predator signals has proven to be a rich hunting ground for evolutionary biologists and cognitive psychologists. Empirical support for a number of classical evolutionary processes, such as kin-selected altruism, aposematism and mimicry, has come from studies of the signals made by prey to potential predators [1]. Perhaps even more striking, the use of different signals for different threats, and their apparently deceptive use for social manipulation, provide tantalising glimpses of the origins of language
5.
6.
7.
8.
References
Animal Behaviour: Strategic Signalling by Cephalopods
Innes C. Cuthill
4.
Ferreira, I., Callaini, G., and Glover, D.M. (2007). DSAS-6 organizes a tube-like centriole precursor, and its absence suggests modularity in centriole assembly. Curr. Biol. 17, 1465–1472. O’Toole, E.T., Giddings, T.H., McIntosh, J.R., and Dutcher, S.K. (2003). Three-dimensional organization of basal bodies from wild-type and delta-tubulin deletion strains of Chlamydomonas reinhardtii. Mol. Biol. Cell 14, 2999–3012. Preble, A.M., Giddings, T.H., and Dutcher, S.K. (2001). Extragenic bypass suppressors of mutations in the essential gene BLD2 promote assembly of basal bodies with abnormal microtubules in Chlamydomonas reinhardtii. Genetics 157, 163–181. Pelletier, L., O’Toole, E., ASchwager, A., Hyman, A.A., and Muller-Reichert, T. (2006). Centriole assembly in Caenorhabditis elegans. Nature 444, 619–623. Matsuura, K., Lefebvre, P.A., Kamiya, R., and Hirono, M. (2004). Bld10p, a novel protein essential for basal body assembly in Chlamydomonas: localization to the cartwheel, the first ninefold symmetrical structure appearing during assembly. J. Cell Biol. 165, 663–671. Hiraki, M., Nakazawa, Y., Kamiya, R., and Hirono, M. (2007). Bld10p constitutes the cartwheel-spoke tip and stabilizes the 9-fold symmetry of the centriole. Curr. Biol. 17, 1778–1783.
and of a ‘Theory of Mind’ (where one individual interprets the behaviour of another in terms of some model of the latter’s intentions or knowledge) [2]. The classic example of strategic anti-predator signalling comes from vervet monkeys’ use of different alarm calls for different predators [3], but instances of the use of different signals for different threats have now been substantiated in a number of vertebrates (see references in [4]). A new experimental study by Keri Langridge and colleagues [4], reported in this issue of Current Biology, adds a new and important
Department of Biochemistry and Biophysics, University of California-San Francisco, 600 16th St., San Francisco, California, USA. E-mail: [email protected] DOI: 10.1016/j.cub.2007.10.038
twist to the field of anti-predator signalling. Not only does it concern a cephalopod mollusc, adding weight to the view that these invertebrates can match many vertebrates in their cognitive and behavioural complexity, but it provides the first clear example of strategic choice with respect to the likely effectiveness of different signals against specific predators. Cuttlefish, like their relatives squid and octopus, have excellent vision and skin pigmentation (and texture) that is under direct and rapid neural control [5]. These attributes allow them unparalleled dynamic camouflage [6], combining general background resemblance, disruptive patterns and posture to achieve near-invisibility in a couple of seconds. But in the face of predators using tactile, olfactory or electromagnetic cues, visual deception may fail and here,