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PubMed1986

Radiation data input for the design of dry or semi-dry U tailings disposal.

Before discussion of design criteria for the handling of dry or semi-dry tailings, it is necessary to obtain an insight into the radiation levels associated with the tailings particles and to study the basic physical properties of dry tailings. This article presents the experimental results of assessing Ra and specific alpha-activity distribution with respect to particle size of the Ranger (RUM) and Nabarlek (QML) uranium mines dry tailings samples. The variation of Rn emanation coefficient versus particle size of dry tailings has also been measured. The nuclear-track detection technique, gamma spectrometry and alpha counting were used for the above measurements. Surface Rn flux from the hypothetical Nabarlek semi-infinite dry tailings pile is 32 Bq m-2 s-1 and the Rn flux for Ranger is 10 Bq m-2 s-1. The theoretical exposure rates for 1 m above these hypothetical tailings piles are 0.95 microC kg-1 h-1 and 0.28 microC kg-1 h-1, respectively. The derived air alpha-contamination limits (DAAC) for the tailings dust were calculated to be 1.2 Bq m-3 for workers and 0.034 Bq m-3 for a member of the public. The limit for workers corresponds to the air tailings dust concentration of 0.79 mg m-3 for QML tailings and 2.2 mg m-3 for RUM tailings. The DAAC limit for the public corresponds to the air tailings dust concentration of 0.022 mg m-3 for QML tailings and 0.064 mg m-3 for RUM tailings.

Air Pollution, Radioactive↗
PubMed1989

Slow inward tail currents in rabbit cardiac cells.

1. A whole-cell gigaseal suction microelectrode voltage-clamp technique has been used to study slow inward tail currents in single myocytes obtained by enzymatic dispersion of rabbit ventricle and atrium. A variety of stimulation protocols, Tyrode solutions and pharmacological agents have been used to test three hypotheses: (a) that the slow inward tail current is generated by an electrogenic Na(+)-Ca2+ exchanger; (b) that a rise in [Ca2+]i, due to release from the sarcoplasmic reticulum can modulate the activity of this exchanger; and (c) that the uptake of calcium by the sarcoplasmic reticulum is a major determinant of the time course of the tail current. 2. As shown previously in amphibian atrium and guinea-pig ventricle, slow inward tail currents can be observed consistently under conditions in which action potentials and ionic currents are recorded using microelectrode constituents which only minimally disturb the intracellular milieu. 3. In ventricular cells, the envelope of these tail currents obtained by varying the duration of the preceding depolarizations shows that (a) the tail currents are activated by pulses as short as 10 ms, and reach a maximum for pulse durations of 100-200 ms, (b) the rate of decay of the tail current gradually increases as the activating depolarizations are prolonged, and (c) the tails cannot be due to deactivation of calcium currents, in agreement with other studies in frog heart. 4. When the mean level of [Ca2+]i is raised following inhibition of the Na(+)-K+ pump by strophanthidin (10(-5) M) or reductions in [K+]o (0.5 mM), the slow inward tail grows in size prior to the onset of a contracture or other signs of calcium-induced toxicity. 5. In a number of different preparations, replacement of [Ca2+]o with BaCl2 markedly or completely inhibits the Na(+)-Ca2+ exchanger, whereas Sr2+ replacement does not have this effect. In myocytes from rabbit ventricle the slow inward tails are reduced significantly and decay more slowly in 0.5-2.2 mM-BaCl2 Tyrode solution, while in 2.2 mM SrCl2 these tails are not altered. 6. The slow inward tail also shows a dependence on [K+]o, corresponding to previous data on Na(+)-Ca2+ exchange in other tissues. Increasing [K+]o in the Tyrode solution to a final concentration of 10-15 mM results in a marked inhibition of the slow tails. This effect cannot be accounted for by changes in the inwardly rectifying potassium current, IK1. 7. The slow tail currents were changed significantly by increasing the temperature of the superfusing Tyrode solution.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2006

The macrophage scavenger receptor CD163: endocytic properties of cytoplasmic tail variants.

CD163 is the monocyte/macrophage-specific receptor for haptoglobin-hemoglobin (Hp-Hb) complexes. The cytoplasmic tail of human CD163 exists as a short tail variant and two long tail variants. Reverse transcriptase-polymerase chain reaction analysis indicated that all three CD163 variants are substantially expressed in blood, liver, and spleen, and the short tail variant is the predominant mRNA species. Using cell transfectants in which cDNA encoding the CD163 variants was inserted at the same site in the genome, we evaluated the expression and endocytic properties of the tail variants. Ligand uptake analysis showed that cells expressing the CD163 short tail variant exhibited a higher capacity for ligand endocytosis than cells expressing the CD163 long tail variants. The difference in endocytic activity was explained by confocal microscopic analysis, showing marked deviations in subcellular distribution. Surface expression was far most pronounced for the CD163 short tail variant, whereas the long tail variants were most abundant in the Golgi region/endosomes. Mutational change of a putative signal for endocytosis (Tyr-Arg-Glu-Met), present in a common part of the cytoplasmic tail of the variants, almost completely inactivated the endocytic activity of the short tail variant. In conclusion, the three physiological tail variants of CD163 may contribute to Hp-Hb endocytosis by means of the common ligand-binding region and endocytic signal. However, the high mRNA expression level and relatively high endocytic capacity of the short tail variant suggest that it accounts for the majority of Hp-Hb uptake from the circulation, whereas the long tail variants may have yet-unknown intracellular roles.

Amino Acid Sequence↗
PubMed2005

Accelerated weathering of biosolid-amended copper mine tailings.

Application of municipal biosolids to mine tailings can enhance revegetation success, but may cause adverse environmental impacts, such as increased leaching of NO3- and metals to ground water. Kinetic weathering cells were used to simulate geochemical weathering to determine the effects of biosolid amendment on (i) pH of leachate and tailings, (ii) leaching of NO3- and SO4(2-), (iii) leaching and bioavailability (DTPA-extractable) of selected metals, and (iv) changes in tailing mineralogy. Four Cu mine tailings from southern Arizona differing in initial pH (3.3-7.3) and degree of weathering were packed into triplicate weathering cells and were unamended and amended with two rates (equivalent to 134 and 200 Mg dry matter ha(-1)) of biosolids. Biosolid application to acid (pH 3.3) tailings resulted in pH values as high as 6.3 and leachate pH as high as 5.7, and biosolids applied to circumneutral tailings resulted in no change in tailing or leachate pH. Concentrations of NO3--N of up to 23 mg L(-1) occurred in leachates from circumneutral tailings. The low pH of the acidic tailing apparently inhibited nitrification, resulting in leachate NO3--N of <5 mg L(-1). Less SO4(2-)-S was leached in biosolid-amended versus unamended acid tailings (final rate of 0.04 compared with 0.11 g SO4(2-)-S wk(-1)). Copper concentrations in leachates from acidic tailings were reduced from 53 to 27 mg L(-1) with biosolid amendment. Copper and As concentrations increased slightly in leachates from biosolid-amended circumneutral tailings. Small increases in DTPA-extractable Cu, Ni, and Zn occurred in all tailings with increased biosolid rate. Overall, there was little evidence of potential for adverse environmental impacts resulting from biosolid application to these Cu mine tailings.

Biological Availability↗
PubMed2005

Role of the prehensile tail during ateline locomotion: experimental and osteological evidence.

The dynamic role of the prehensile tail of atelines during locomotion is poorly understood. While some have viewed the tail of Ateles simply as a safety mechanism, others have suggested that the prehensile tail plays an active role by adjusting pendulum length or controlling lateral sway during bimanual suspensory locomotion. This study examines the bony and muscular anatomy of the prehensile tail as well as the kinematics of tail use during tail-assisted brachiation in two primates, Ateles and Lagothrix. These two platyrrhines differ in anatomy and in the frequency and kinematics of suspensory locomotion. Lagothrix is stockier, has shorter forelimbs, and spends more time traveling quadrupedally and less time using bimanual suspensory locomotion than does Ateles. In addition, previous studies showed that Ateles exhibits greater hyperextension of the tail, uses its tail to grip only on alternate handholds, and has a larger abductor caudae medialis muscle compared to Lagothrix. In order to investigate the relationship between anatomy and behavior concerning the prehensile tail, osteological data and kinematic data were collected for Ateles fusciceps and Lagothrix lagothricha. The results demonstrate that Ateles has more numerous and smaller caudal elements, particularly in the proximal tail region. In addition, transverse processes are relatively wider, and sacro-caudal articulation is more acute in Ateles compared to Lagothrix. These differences reflect the larger abductor muscle mass and greater hyperextension in Ateles. In addition, Ateles shows fewer side-to-side movements during tail-assisted brachiation than does Lagothrix. These data support the notion that the prehensile tail represents a critical dynamic element in the tail-assisted brachiation of Ateles, and may be useful in developing inferences concerning behavior in fossil primates.

Animals↗
PubMed1992

Axonal sprouting and frank regeneration in the lizard tail spinal cord: correlation between changes in synaptic circuitry and axonal growth.

In our previous studies, we found that the number of supraspinal neurons projecting to the level of tail spinal cord increases by 74% during tail regeneration and that the number of local spinal neurons with descending projections increases 233%. However, only a small fraction of the supraspinal axons (less than 4%) and half of the local spinal axons actually enter the regenerated spinal cord. We suggested that this may be the result of "synaptic capture" in which regrowing axons make synapses on denervated targets rostral to the transection, aborting further regeneration. To examine this hypothesis, morphometric analysis of electron microscope (EM) photomontages was used to test for changes in synaptic distribution on ventral horn neurons rostral to regenerating tail spinal cord. In addition, 3H-thymidine and retrograde markers were used to determine whether the regenerate axons arose from cut axons, neurogenesis, or sprouting from uninjured neurons. 3H-thymidine injections during regeneration, combined with retrograde HRP pathway tracing, did not reveal the production of new neurons in the tail spinal cord. To test whether cut axons regenerate, fluorescein isothiocyanate conjugated latex beads were applied to the exposed end of the tail spinal cord. After tail regeneration, HRP was applied to the new spinal cord in the regenerated tail. Examination of local spinal neurons (the primary source of axons that enter the regenerated tail spinal cord) revealed that 28% of the neurons contained both labels. This indicated that cut axons successfully regrew into the new tail spinal cord. The regenerated axons that fail to enter the new tail spinal cord can be found in the normal spinal cord immediately rostral to the regenerated tail. To determine whether these axons were making synaptic contacts, lamina IX ventral horn neurons were examined. EM photomontages of the spinal cord rostral to the regenerate tail revealed the following properties: (1) neurons rostral to regenerated tails are larger in area compare to non-regenerates (mean increase = 112%); (2) axosomatic contacts cover a greater percentage of the neuronal soma following regeneration compared to normal (mean increase = 23%); and (3) this increased innervation is the result of an increase in the number of synaptic boutons rather than larger boutons. The number of synaptic contacts in regenerated lizards returned to normal following lumbar transection, indicating that supraspinal and/or long descending propriospinal afferents were the major source of the increased synaptic contacts.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1996

Muscle activity in autotomized tails of a lizard (Gekko gecko): a naturally occurring spinal preparation.

We quantified muscle activity in tails of lizards (Gekko gecko) during running and after autotomy of the tail. We chose different animals and varied where we broke the tails in order to obtain three experimental preparations having: no regenerated tissue or prior tail loss (non-regenerated), a large regenerated portion and a few original caudal vertebrae (partially regenerated), and only regenerated tissue (fully regenerated). All observed axial motor patterns were rhythmic. During running of intact animals, muscles in non-regenerated tails were activated in an alternating, unilateral pattern that was propagated posteriorly. After autotomy, non-regenerated tails had unilateral muscle activity that alternated between the left and right sides and propagated anteriorly. Autotomized, partially regenerated tails had unilateral, alternating muscle activity that lacked any longitudinal propagation. Autotomized, fully regenerated tails had periodic muscle activity that occurred simultaneously for both left and right sides and all longitudinal positions. Neither tactile stimulation nor removal of the tail tip prior to autotomizing the tail affected the motor pattern. Several features of the motor pattern of autotomized tails changed significantly with increased time after autotomy. Autotomized tails with one or more spinal segments moved longer and more vigorously than autotomized tails consisting entirely of regenerated (unsegmented) tissue.

Animals↗
PubMed1999

Neuronal pathways for spinal reflexes activated by group I and group II muscle afferents in the spinal segment (Co1) innervating the tail in the low spinalized cat.

We studied neuronal pathways for spinal reflexes activated by group-I and group-II muscle afferents in the spinal segments innervating the tail in unanesthetized and spinalized (L1) cats. Experiments were performed on 25 adult cats of both sexes. The effects of stimulating nerves innervating six tail muscles on both sides were recorded from tail motoneurons in the first coccygeal spinal segment (Co1) using glass microelectrodes. Stable recordings were obtained from 150 tail motoneurons. Stimulation of group-1 muscle afferents (stimulus intensity <1.8 T) often produced EPSPs (82/150) after stimulating nerves innervating neighboring tail muscles. Motoneurons innervating the long-tendoned muscles, M. extensor caudae lateralis and M. flexor caudae longus (ECL and FCL), received heteronymous monosynaptic connections from group-I muscle afferents innervating the ipsilateral tail muscles. The motoneurons innervating segmental muscles, M. extensor caudae medialis and M. flexor caudae brevis (ECM and FCB), received heteronymous monosynaptic connections from group-I muscle afferents innervating tail muscles on both sides. The motoneurons innervating tail muscles originated from the Ossa coxae, M. abductor caudae externus and M. abductor caudae internus (ACE and ACI), received monosynaptic connection from group-I muscle afferents innervating most of the tail muscles on both sides. Crossed disynaptic inhibitory pathways activated by primary muscle afferent inputs were observed in ECM, ACE, FCL, and FCB motoneurons. The effects of group-II afferent inputs were not dependent on the kind of motoneuron, and alternative excitatory and inhibitory pathways were not clearly observed in the tail motoneuron pool. It is suggested that variability of the neuronal pathways from group-I and -II muscle afferents to tail motoneurons corresponds to functional relationships among tail muscles, depending on the tail movements.

Animals↗
PubMed1985

Genetic analysis of subunit assembly of the tail fiber of bacteriophage T3.

Bacteriophage T3 virions have six tail fibers composed of the product of gene 17 (gp17). Each tail fiber is a trimer of gp17 polypeptide. To characterize the assembly process of the tail fiber, temperature-sensitive (ts) mutants of gene 17 (ts17) were analyzed by SDS-polyacrylamide gel electrophoresis and by extract complementation. Newly synthesized gp17 polypeptide chains matured to SDS-resistant native trimers with a half time of about 7.5 min at 30 degrees. Although all ts17 mutants had similar plating efficiencies at restrictive temperature (41.5 degrees or 42 degrees), they showed different phenotypes. tsNG75, whose mutation was located in the carboxyl-terminal region of gene 17, was defective in trimer assembly at 41.5 degrees. The ts tail fibers formed at 30 degrees lost the ability to attach to the tail upon treatment at 41.5 degrees. There was a change in temperature sensitivity of tsNG75 tail fibers upon attachment to the tail, suggesting that the tail fiber may change conformation after attachment to the tail. tsNG215 and tsNG169, whose mutation sites were located in the amino-terminal region of gene 17, were not defective in the trimer assembly and attachment to the tail at the restrictive temperature. tsNG215 tail fibers formed at 41.5 degrees appear to be aberrant because they were not active in extract complementation and their attachment to fiberless particles resulted in production of noninfectious phage. Tail fibers produced by cells infected with tsNG169 at the restrictive temperature were active in extract complementation. Phage particles were formed in tsNG169-infected cells at the restrictive temperature. These particles were infectious at the permissive temperature and the mutant was non-infectious only if infection was continued at the restrictive temperature. These phenotypic differences exhibited by different gene 17 mutants may indicate the regions within the gene 17 polypeptide that play a role(s) in the folding and assembly of gp17 and in the biological activity of the mature tail fiber.

Electrophoresis, Polyacrylamide Gel↗
PubMed2006

Novel gain-of-function alleles demonstrate a role for the heterochronic gene lin-41 in C. elegans male tail tip morphogenesis.

To gain an understanding of the genes and mechanisms that govern morphogenesis and its evolution, we have analyzed mutations that disrupt this process in a simple model structure, the male tail tip of the rhabditid nematode C. elegans. During the evolution of rhabditid male tails, there have been several independent changes from tails with rounded tips ("peloderan", as in C. elegans) to those with pointed tips ("leptoderan"). Mutations which produce leptoderan (Lep) tails in C. elegans thus identify candidate genes and pathways in which evolutionary changes could have produced leptoderan tails from peloderan ancestors. Here we report that two novel, gain-of-function (gf) alleles of lin-41 have lesions predicted to affect the N-terminus of the RBCC-domain LIN-41 protein. Both gf alleles cause the tail tip of adult males to retain the pointed shape of the juvenile tails, producing a Lep phenotype that looks like the tails of leptoderan species. Consistent with its role in the heterochronic pathway, we find that lin-41 governs the timing and extent of male tail tip morphogenesis in a dose-dependent manner. Specifically, the Lep phenotype results from a heterochronic delay in the retraction and fusion of the tail tip cells during L4 morphogenesis, such that retraction is not completed before the adult molt. Conversely, we find that tail tip morphogenesis and cell fusions begin precociously at the L3 stage in the reduced-function lin-41 mutant, ma104, resulting in over-retracted male tails in the adult. Because modulated anti-LIN-41 RNAi knockdowns in the gf mutants restore wild-type phenotype, we suggest that the leptoderan phenotype of the gf alleles is due to a higher activity of otherwise normal LIN-41. Additionally, the gf allele is suppressed by the wild-type allele, suggesting that LIN-41 normally regulates itself, possibly by autoubiquitination. We speculate that small changes affecting LIN-41 could have been significant for male tail evolution.

Alleles↗
PubMed1998

The influence of tail autotomy on agonistic behaviour in a territorial salamander.

Assessment of potentially asymmetrical characters (such as fighting ability and resident advantage) is often important in determining the outcome of agonistic interactions. Loss of body parts, a predator defence mechanism used by many animals, may lead to a reduction in fighting ability and may be easily assessed by competitors. We investigated the influence of tail loss on the expression of agonistic behaviour in the territorial red-backed salamander, Plethodon cinereus. Residents and intruders were matched for body size, and pairs were tested in all combinations of tailed or tailless residents with tailed or tailless intruders. Neither residents nor intruders altered their behaviour based on their own tail condition, but they did alter their behaviour based on the tail condition of their opponents. Intruders showed more aggression or less submission towards tailless residents than towards tailed residents. When contests were between residents and intruders of the same tail condition (both tailed or tailless), intruders were more aggressive towards residents when both were tailless than when both were tailed, indicating that tail loss does not directly hamper aggressive displays. In contests where the asymmetry between residents and intruders was small (based on tail condition and residency status), intruders showed more aggression and less submission than in contests where the asymmetry was large. Residents did not differ in their behaviour for most comparisons. Thus, for intruders, the tail condition of residents is an important determinant of agonistic behaviour displayed in territorial contests. For residents, factors other than tail condition (such as resource value) may be more likely to influence their behaviour. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1994

Influence of hydrocarbon tail structure on quinone binding and electron-transfer performance at the QA and QB sites of the photosynthetic reaction center protein.

Binding free energies of 37 functional replacement quinone cofactors with systematically altered hydrocarbon tail structures have been determined for the QA and QB redox catalytic sites of the reaction center protein isolated from Rhodobacter sphaeroides and solubilized in aqueous and in hexane solutions. The first two and part of the third isoprene units of the 10-unit tail of the native ubiquinone-10 cofactor interact with the protein interior at each site. Contributions of the same tail structures to the binding free energies of quinones at the QA and QB sites are comparable, suggesting that the binding domains share common features. Comparison of the affinities of a homologous series of 10 n-alkyl-substituted ubiquinones resolves the binding forces along the length of the tail binding domain and shows that strong steric constraints oppose accommodation of the tail in its extended conformation. Differences in the contributions of identical tail substituents to ubiquinone- and menaquinone-QA site affinities, and tail-induced changes of up to 5-fold in the rates of QA site-mediated electron-transfer reactions, suggest that the tail adjusts the position of the quinone ring. Substitution of ubiquinone with the native 10-unit isoprene tail does not alter the affinity for the sites as determined in hexane solution. However, one- and two-isoprene-substituted quinones bind more tightly than analogs substituted with saturated-alkyl tail substituents. The sites therefore exhibit binding specificity for the native isoprene tail structure. Calculations indicate that the binding specificity arises primarily from a lower integrated torsion potential energy in the bound isoprene tails. The results suggest that the in vivo tail-protein interaction is designed to deter competitive interference of quinone function by amphiphilic species present in the native membrane.

Crystallography, X-Ray↗
PubMed2004

Suppression of integrin activation by the membrane-distal sequence of the integrin alphaIIb cytoplasmic tail.

Integrin cytoplasmic tails regulate integrin activation including an increase in integrin affinity for ligands. Although there is ample evidence that the membrane-proximal regions of the alpha and beta tails interact with each other to maintain integrins in a low-affinity state, little is known about the role of the membrane-distal region of the alpha tail in regulation of integrin activation. We report a critical sequence for regulation of integrin activation in the membrane-distal region of the alphaIIb tail. Alanine substitution of the RPP residues in the alphaIIb tail rendered alphaIIbbeta3 constitutively active in a metabolic energy-dependent manner. Although an alphaIIb/alpha6Abeta3 chimaeric integrin, in which the alphaIIb tail was replaced by the alpha6A tail, was in an energy-dependent active state to bind soluble ligands, introduction of the RPP sequence into the alpha6A tail inhibited binding of an activation-dependent antibody PAC1. In alphaIIb/alpha6Abeta3, deleting the TSDA sequence from the alpha6A tail or single amino acid substitutions of the TSDA residues inhibited alphaIIb/alpha6Abeta3 activation and replacing the membrane-distal region of the alphaIIb tail with TSDA rendered alphaIIbbeta3 active, suggesting a stimulatory role of TSDA in energy-dependent integrin activation. However, adding TSDA to the alphaIIb tail containing the RPP sequence of the membrane-distal region failed to activate alphaIIbbeta3. These results suggest that the RPP sequence after the GFFKR motif of the alphaIIb tail suppresses energy-dependent alphaIIbbeta3 activation. These findings provide a molecular basis for the regulation of energy-dependent integrin activation by alpha subunit tails.

Amino Acid Sequence↗
PubMed2002

Beta-catenin N- and C-terminal tails modulate the coordinated binding of adherens junction proteins to beta-catenin.

beta-Catenin plays a central role in the establishment and regulation of adherens junctions because it interacts with E-cadherin and, through alpha-catenin, with the actin cytoskeleton. beta-Catenin is composed of three domains: a central armadillo repeat domain and two N- and C-terminal tails. The C-tail interacts with the armadillo domain and limits its ability to bind E-cadherin and other cofactors. The two beta-catenin tails are mutually inter-regulated because the C-tail is also necessary for binding of the N-tail to the armadillo domain. Moreover, the N-tail restricts the interaction of the C-tail with the central domain. Depletion of either of the two tails has consequences for the binding of factors at the other end: deletion of the C-tail increases alpha-catenin binding, whereas deletion of the N-tail blocks E-cadherin interaction to the armadillo repeats. As an effect of the interconnection of the tails, the association of alpha-catenin and E-cadherin to beta-catenin is interdependent. Thus, binding of alpha-catenin to the N-tail, through conformational changes that affect the C-tail, facilitates the association of E-cadherin. These results indicate that different cofactors of beta-catenin bind coordinately to this protein and indicate how the two terminal ends of beta-catenin exquisitely modulate intermolecular binding within junctional complexes.

Amino Acid Sequence↗
PubMed2003

Evolution of the structure of tail feathers: implications for the theory of sexual selection.

Bird tails are extraordinarily variable in length and functionality. In some species, males have evolved exaggeratedly long tails as a result of sexual selection. Changes in tail length should be associated with changes in feather structure. The study of the evolution of feather structure in bird tails could give insight to understand the causes and means of evolution in relation to processes of sexual selection. In theory, three possible means of tail length evolution in relation to structural components might be expected: (1) a positive relationship between the increase in length and size of structural components maintaining the mechanical properties of the feather; (2) no relationship; that is, enlarging feather length without changes in the structural components; and (3) a negative relationship; that is, enlarging feather length by reducing structural components. These hypotheses were tested using phylogenetic analyses to examine changes in both degree of exaggeration in tail length and structural characteristics of tail feathers (rachis width and density of barbs) in 36 species, including those dimorphic and nondimorphic in tail length. The degree of sexual dimorphism in tail length was negatively correlated with both rachis width and density of barbs in males but not in females. Reinforcing this result, we found that dimorphism in tail length was negatively associated with dimorphism in tail feather structure (rachis width and density of barbs). These results support the third hypothesis, in which the evolution of long feathers occurs at the expense of making them simpler and therefore less costly to produce. However, we do not know the effects of enfeeblement on the costs of bearing. If the total costs increased, the enfeeblement of feathers could be explained as a reinforcement of the honesty of the signal. Alternatively, if total costs were reduced, the strategy could be explained by cheating processes. The study of female preferences for fragile tail feathers is essential to test these two hypotheses. Preferences for fragile tails would support the evolution of reinforcement of honesty, whereas female indifference would indicate the existence of cheating in certain stages of the evolutionary process.

Animals↗
PubMed2000

Ultrastructure of Rickettsia rickettsii actin tails and localization of cytoskeletal proteins.

Actin-based motility (ABM) is a mechanism for intercellular spread that is utilized by vaccinia virus and the invasive bacteria within the genera Rickettsia, Listeria, and Shigella. Within the Rickettsia, ABM is confined to members of the spotted fever group (SFG), such as Rickettsia rickettsii, the agent of Rocky Mountain spotted fever. Infection by each agent induces the polymerization of host cell actin to form the typical F (filamentous)-actin comet tail. Assembly of the actin tail propels the pathogen through the host cytosol and into cell membrane protrusions that can be engulfed by neighboring cells, initiating a new infectious cycle. Little is known about the structure and morphogenesis of the Rickettsia rickettsii actin tail relative to Shigella and Listeria actin tails. In this study we examined the ultrastructure of the rickettsial actin tail by confocal, scanning electron, and transmission electron microscopy. Confocal microscopy of rhodamine phalloidin-stained infected Vero cells revealed the typhus group rickettsiae, Rickettsia prowazekii and Rickettsia typhi, to have no actin tails and short (approximately 1- to 3-micrometer) straight or hooked actin tails, respectively. The SFG rickettsia, R. rickettsii, displayed long actin tails (>10 micrometer) that were frequently comprised of multiple, distinct actin bundles, wrapping around each other in a helical fashion. Transmission electron microscopy, in conjunction with myosin S1 subfragment decoration, revealed that the individual actin filaments of R. rickettsii tails are >1 micrometer long, arranged roughly parallel to one another, and oriented with the fast-growing barbed end towards the rickettsial pole. Scanning electron microscopy of intracellular rickettsiae demonstrated R. rickettsii to have polar associations of cytoskeletal material and R. prowazekii to be devoid of cytoskeletal interactions. By indirect immunofluorescence, both R. rickettsii and Listeria monocytogenes actin tails were shown to contain the cytoskeletal proteins vasodilator-stimulated phosphoprotein profilin, vinculin, and filamin. However, rickettsial tails lacked ezrin, paxillin, and tropomyosin, proteins that were associated with actin tails of cytosolic or protrusion-bound Listeria. The unique ultrastructural and compositional characteristics of the R. rickettsii actin tail suggest that rickettsial ABM is mechanistically different from previously described microbial ABM systems.

Actins↗
PubMed1983

Bacteriophage SPO1 structure and morphogenesis. I. Tail structure and length regulation.

Bacteriophage SPO1, a structually complex phage with hydroxymethyl uracil replacing thymine, has been studied by structural and chemical methods with the aim of defining the virion organization. The contractile tail of SPO1 consists of a complex baseplate, a tail tube, and a 140-nm-long sheath composed of stacked disks (4.1 nm repeat), each containing six subunits of molecular weight 60,300. The subunits are arranged in six parallel helices, each with a helical screw angle (omega 0) of 22.5 degrees. The baseplate was shown to undergo a structural rearrangement during tail contraction into a hexameric pinwheel. A mutation in gene 8 which produced unattached heads and tails also produced tails of different lengths. The tail length distribution suggests that the smallest integral length increment is a single disk of subunits. The structural arrangement of subunits in long tails is identical to that of normal tails, and the tails can contract. Many of the long tails showed partial stain penetration within the tail tube to a point which coincides with the top of a unit-length tail. The implications of these findings with respect to tail length regulation are discussed.

Bacillus subtilis↗
PubMed1999

Expression of the myosin heavy chain genes in the tail muscle of thyroid hormone-induced metamorphosing Rana catesbeiana tadpoles.

In tadpoles of the North American bullfrog, Rana catesbeiana, spontaneous and thyroid hormone (T3)-induced metamorphosis is characterized by regression of the tail, which is preceded by a decrease in total protein synthesis in tail tissues. We have demonstrated that thyroid hormone treatment of a tadpole does not affect the synthesis of all proteins equally in the tadpole tail muscle. For example, the synthesis of myosin heavy chains (MHCs) is depressed within 1 day and decreases to 45% of control values after 5 days of T3 treatment, whereas the decreased synthesis of soluble muscle proteins is transient and returns to above control levels by day 5. To determine whether the hormone-induced decrease in MHC synthesis is the result of changes in the transcription of translation of MHC mRNAs, we isolated cDNAs complementary to five different MHC mRNAs from a tail muscle cDNA library and used them to examine the levels of each MHC mRNA in the tail muscle of T3-treated tadpoles. mRNAs that recognize the cDNAs for these five different MHCs are all expressed in the tadpole tail and limb muscles, as well as in the adult leg muscles. MHC mRNAs unique to tadpole tail were not detected. Interestingly, the relative amounts of mRNA for four of the five MHCs increase in tail muscle after T3 treatment of the tadpole, suggesting that repression of MHC gene expression at the protein level does not result from a decrease in the amount of MHC mRNAs. Rather, these results support the contention that the decreased synthesis of MHCs in the tail muscle of T3-treated tadpoles is caused by this hormone, either directly or indirectly, depressing the translation of the MHC mRNAs in this tissue. These results, coupled with the observation that the synthesis of soluble muscle proteins is depressed only in a transient fashion, suggest that T3 may be initiating the expression of a gene(s) that encodes a protein(s) responsible for inhibiting the translation of the MHCs and, perhaps, other structural proteins in the tadpole tail muscle. Whatever the case, the translational regulation of MHC synthesis occurs well before any degradation of the tail tissue is evident and appears to be one of the earliest events in the hormone-induced cell death program of the tadpole tail muscle.

Amino Acid Sequence↗