Mirror-image Symmetry Research Articles

Localization of nanos RNA controls embryonic polarity

Anterior-posterior polarity of the Drosophila embryo is initiated during oogenesis through differential maternal RNA localization. The RNA of the anterior morphogen bicoid is localized to the anterior pole of the embryo, where bicoid protein controls head and thorax development. The RNA of the posterior morphogen nanos is localized to the posterior pole, where nanos protein is required for abdomen formation. Here we show that the nanos 3′ untranslated region, like that of the bicoid RNA, is sufficient for RNA localization. We have used the bicoid RNA localization signal to mislocalize nanos, producing embryos with two sources of nanos protein. Such embryos form two abdomens with mirror image symmetry. Embryos with nanos RNA localized only to the anterior have greater nanos gene activity than embryos with nanos RNA localized posteriorly. We propose a role for RNA localization in regulating nanos activity.

Orthodistichous phyllotaxy and dorsiventral symmetry on adult shoots of Cyclanthus bipartitus (Cyclanthaceae, Monocotyledoneae)

An adult shoot of Cyclanthus bipartitus may simultaneously exhibit orthodistichy and dorsiventral symmetry, i.e., adult features previously unreported for Cyclanthus. As in previously investigated adult shoots of C. bipartitus with spirodistichous phyllotaxy, specimens presently described have sympodial rhizomes that form renewal shoots and terminal inflorescences. The phyllotaxy, symmetry, and sympodial structure of these specimens, collectively, represent a new type of growth habit in the Cyclanthaceae. On a shoot with orthodistichy the basal portions of mature leaves define a concave surface, convex surface, sagittal plane, and frontal plane. Plants grow upright on forest-covered slopes, and the concave surface and convex surface of a shoot are slope-opposed and slope-facing, respectively. Most emergent adventitious roots arise from the convex surface. Aspects of the form, symmetry, development, and orientation of a shoot are interpretable as adaptations to unequal illumination on its slope-facing versus slope-opposed sides. Presence of conspicuous dorsiventral symmetry is correlated with poorly expressed mirror-image symmetry, and shoots are neither left-handed nor right-handed, contrary to the condition in various Cyclanthaceae. Present findings bolster the conclusion that C. bipartitus is an extremely variable species. Key words: Cyclanthaceae, Cyclanthus, morphology, symmetry, phyllotaxy.

Normal and teratological pistillate spikes of Typha angustifolia (Typhaceae): gross aspects of morphology, anatomy, symmetry, and inflorescence dehiscence

Normal and teratological pistillate spikes of Typha angustifolia were found at the same locality in Ohio, U.S.A., and the individual spikes exhibited radial, dorsiventral, and mirror-image symmetry, as well as polarity. Dorsiventral symmetry provided a frame of reference for comparing normal and teratological individuals. Both kinds of pistillate spikes were interpreted to have dorsal and ventral surfaces, sagittal and frontal planes, right and left sides, length, width, and height. Present in teratological spikes, but absent from normal ones, were either split(s) within the central stem axis or exceptionally long type-1 furrow(s). Split(s) or type-1 furrow(s) divided a teratological spike longitudinally into two to five subunits. Where two subunits were present, division was solely along the sagittal plane, whereas spikes with three to five subunits were divided along the sagittal plane and along, or parallel to, the frontal plane. In the case of teratological spikes with two to four subunits it was possible to number and compare subunits in a consistent manner. On some teratological spikes after splitting, subunits had become bowed, rotated, and curled or folded. Apparently, in teratological spikes, indentations and type-1 and type-2 furrows along the sagittal plane function, collectively, as a line of dehiscence. Key words: Typha, morphology, anatomy, symmetry, inflorescence, dehiscence.

F-centre luminescence from BaF 2

We have observed a new broad-band luminescence, with a peak at 626.5 nm, additively-coloured BaF 2, but only when exciting on the long wavelength side of the F-centre absorption band. Such emission could originate in one of the many complex centres which are created in such materials by additive colouration. However, the special conditions required for its observation as well as the mirror-image symmetry of the emission band with respect to the F-centre absorption band suggest that the emission may originate in isolated F-centres. To our knowledge, such emission has not been reported for any of the alkaline-earth fluorides.

Corneal Topography of Keratoconus

Sixty-three eyes of 49 patients with keratoconus were studied by means of computer-assisted corneal topographic analysis. Two patients with keratoconus in one eye had no topographic evidence of keratoconus in the opposite eye. Keratoconic topographic alterations were classified into two groups. The majority of the patients (72%) had peripheral cones, with steepening extending to the limbus. In this group, the steepening was commonly restricted to one or two quadrants. In some cases, however, the changes involved nearly the entire corneal surface. The remaining group (about one quarter of the keratoconus patients) had steepening that was restricted to the central cornea. In either group, the topographic alterations in the two eyes of any single patient were characterized by a high degree of nonsuperimposable mirrorimage symmetry (enantiomorphism). In the majority of patients, however, there was a large and statistically significant disparity between the two eyes in the power at the apex of the cone and the total cylinder [mean differences 8.2 ± 6.0 D (p < 0.0001) and 4.3 ± 2.7 D (p < 0.0001), respectively].

Corneal Topography of Keratoconus

Sixty-three eyes of 49 patients with keratoconus were studied by means of computer-assisted corneal topographic analysis. Two patients with keratoconus in one eye had no topographic evidence of keratoconus in the opposite eye. Keratoconic topographic alterations were classified into two groups. The majority of the patients (72%) had peripheral cones, with steepening extending to the limbus. In this group, the steepening was commonly restricted to one or two quadrants. In some cases, however, the changes involved nearly the entire corneal surface. The remaining group (about one quarter of the keratoconus patients) had steepening that was restricted to the central cornea. In either group, the topographic alterations in the two eyes of any single patient were characterized by a high degree of nonsuperimposable mirror-image symmetry (enantiomorphism). In the majority of patients, however, there was a large and statistically significant disparity between the two eyes in the power at the apex of the cone and the total cylinder [mean differences 8.2 +/- 6.0 D (p less than 0.0001) and 4.3 +/- 2.7 D (p less than 0.0001), respectively].

Morphology of Dianthoveus cremnophilus (Cyclanthaceae)

Dianthoveus cremnophilus exhibits terminal inflorescences and rhizomes composed of renewal shoots. A rhizome bears two kinds of vegetative buds directly, viz. renewal buds that form renewal shoots and nonrenewal buds that may develop into new rhizomes. Adult leaves consist of sheath, petiole, transition zone, and a bifid lamina that varies from unicostate to subtricostate. The inflorescence axis consists of peduncle and spadix and bears two kinds of spathes, conspicuous and inconspicuous. Seeds exhibit four outer cell layers and become split periclinally throughout the third layer, as well as longitudinally down to this layer, along one edge. Tissue outside the region of splitting may be abscinded; wall ingrowths of the ruptured third layer adhere to, and appear outermost on, the remaining portion of seed, where they directly contact the environment. Seedlings exhibit a primary root, very short hypocotyl, cotyledon, and epicotyl with plumular leaves. Shoots manifest substantial mirror-image symmetry.

Mirror-Image and Invariant Distributions in ARMA Models

The finite sample distributions of estimators and test statistics in ARMA time series models are generally unknown. For typical sample sizes, the approximations provided by asymptotic distributions are often unsatisfactory. Hence simulation or numerical integration methods are used to investigate the distributions. In practice only a limited part of the parameter space is examined using these methods. Thus any results which allow us to infer properties from one portion of the parameter space to another or to establish symmetry are most welcome.For the ARMA model estimated with no intercept term, we show that the least-squares and maximum likelihood estimators have mirror-image invariant or symmetric distributions. The F, t, likelihood ratio, Wald, and Lagrange multiplier statistics are also shown to have distributions with certain mirror-image invariant or symmetry properties. The analysis is extended to misspecified models as well as to ARMA spectral densities.These properties would have been helpful in either simplifying or extending much earlier work in this area.

Theoretical analysis of Franck-Condon and vibronic activity of the a g and b 3g modes in the S 0↔ S 1 transitions in anthracene

The QCFF/PI method and the CNDO/S+CISD method in the floating atomic orbital basis set are used to study Franck-Condon and vibronic activity of the a g and b 3g modes of anthracene in the S 0 ↔ S 1 transition. The calculated intensities of the a g and b 3g fundamentals in the absorption and emission spectra agree reasonably well with the experimental intensities. Modes 6 (a g) and 3 (b 3g) are shown to be the most vibronically active modes in the S 0 ↔ S 1 transition. The calculations indicate that upon excitation to the 1B 1u ( 1L a) state some modes mix strongly. This mixing is shown to be the main source of the breakdown of the mirror-image symmetry between the absorption and emission spectra.

Positional signalling and the development of the humerus in the chick limb bud.

The positional signal model for specification of the cartilaginous elements in limb development has been tested by examining the effect on the humerus of grafting a polarizing region to different positions along the anteroposterior axis of the limb bud at stage 16. The humerus between the host and grafted polarizing region was largely normal though there were variations in width, particularly the distal epiphysis. The humerus often showed mirror-image symmetry along the anteroposterior axis. When the grafted polarizing region was in a very anterior position, there were a few cases where a second humerus developed. Anterior to the graft an additional humerus often developed. This was associated with the splitting of the bud into two domains. It is suggested that these results are not consistent with a positional signal model and that an additional mechanism involving an isomorphic prepattern may be involved in the specification of the cartilaginous elements.

The phonotactic patterning of pennsylvania dutch consonants

Click to increase image sizeClick to decrease image size SUMMARY This paper deals with two aspects of Pennsylvania Dutch. The first section outlines the sociocultural features of Amish society within which Pennsylvania Dutch is spoken. The second section gives an outline of the phonotactic patterning of the initial and final consonants used in Pennsylvania Dutch. The conclusions presented here are based on an analysis of spoken language recorded by the author in Lancaster County PA in 1985, and on recordings of Pennsylvania Dutch listener participation radio, programs. Information has also been cross checked in or derived from a number of traditional grammars of Pennsylvania Dutch. This phonotactic analysis focuses on the permissible consonants and consonant clusters which are used in the syllable initial and syllable final positions of Pennsylvania Dutch. Some attention has also been given to instances of phonetic variation and to a number of processes such as na-za1ization, apocope and cluster simplification that distort the phonotactic mirror image symmetry of initial and final consonants and clusters in Pennsylvania Dutch. The data base in hand however did not permit a quantitative analysis of such variation or processes. Neither has the effect of American English on Pennsylvania Dutch been analized in this paper.

Percussion air motor

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Stagewise decline in the activity of brain protein synthesis factors and relationship between this decline and longevity in two rodent species

The activities of brain initiation factor 2 and brain elongation factor 1, which function as rate-limiting in total protein synthesis, and estimations of brain weight were followed during postnatal life in the rat and the mouse. Both activities decreased in parallel while cumulative brain weight increased. Three exponential components were required for the mathematical expression of each of the three processes in semilogarithmic plots against time. The acceleration curves for the activities and tissue weight demonstrated a mirror image symmetry. Within the general pattern of diminution with age, the negative acceleration of the activities and the positive acceleration of the brain weight displayed repeated bursts. The activities of both factors could also be arranged into several regression lines in log/log plots against time. Significantly, in these plots, the regression line calculated for the whole set of data for each factor activity showed that the value of the ratio of the slopes (mouse to rat) was inversely related to the square root of the ratio of species longevity and was in agreement with the power law relating life spans of cells to species longevity (Röhme, Proc. Natl. Acad. Sci. U.S.A., 78 (1981)5009).

Cloning sequences from the hairy gene of Drosophila.

A series of mutations that alter the pattern of segmentation in Drosophila embryos has been identified. Mutations in one of these loci, hairy, delete the posterior part of each odd-numbered segment and the anterior part of each even-numbered segment; although the amount deleted depends on the allele. Weak alleles delete less than an entire segment and do not always eliminate structures in every other segment. Strong alleles show the same periodicity in the pattern defect, but delete regions greater than one segment. In such cases the remaining parts of the pattern duplicate with mirror-image symmetry. To study the function of this gene at a molecular level, sequences from the hairy locus were cloned. This was facilitated by the hairy1 (h1) mutation, which is caused by the insertion of the transposable element, gypsy.

Reconstruction of signals from phase: Efficient algorithms, segmentation, and generalizations

In this paper, we develop several new formulations of the phase-only reconstruction problem which lead to new, efficient algorithms for signal reconstruction. We describe a procedure for approximately reconstructing a long duration signal from short segments. Phase-only blind deconvolution for linear phase filters relies on mirror image symmetry in the filter transfer function H(z). We generalize this deconvolution result to include several other types of symmetries for H(z).

Are circadian oscillators structurally unstable?

The common belief is that all biological oscillations are of limit cycle type. It is shown in this article that the phase response curves simulated on a two-species Lotka-Volterra linear (i.e. non-limit cycle type) oscillator, do look similar to those obtained by experimental methods by different workers. The form of the phase response curves, the existence of singularities and the mirror-image symmetry of opposite perturbations are modelled on the Lotka-Volterra system. The study, which is strongly indicative of the possibility that the underlying oscillator (or oscillators) is (are) not structurally stable, also indicates the necessity of designing critical experiments, capable of distinguishing between limit cycle and non-limit cycle oscillators, since the single-pulse phase resetting does nothing to distinguish between them.

The origin of mirror-image symmetry doublet cells in the hypotrich ciliateParaurostyla weissei.

Mirror-image doublets of the hypotrich ciliateParaurostyla weissei were induced by modifying culture conditions. Successive steps of doublet formation involve inhibiting the separation of daughter cells during cell division and the shifting of these to attain a parallel configuration. The posterior part of the adoral band of membranelles in the right component then turns to the left and fuses with the distal terminal of the membranellar band in the left component. In effect, part of the adoral band and some of the paroral membranelles become apposed upside down, and the paroral membranelles of the right component are located on the left side of the adoral membranelles. A new site of oral primordium formation is initiated at the junction of the two oral apparatuses, the ciliature of which is arranged in a mirror-image pattern. During further cortical reorganization, the whole body ciliature of the right component becomes organized as a mirror-image of the normal left component.Both components of the doublet show the same ultrastructure of body ciliature and lack the right marginal cirri; the symmetry-reversal half, however, possesses multiple rows of left marginal cirri. The individual adoral membranelles and paroral membranelles in the symmetry-reversal component are rotated anteroposteriorly. Some aspects of the patterning of cortical structures are discussed.

Heteropolymer filaments of vimentin and desmin in vascular smooth muscle tissue and cultured baby hamster kidney cells demonstrated by chemical crosslinking.

Certain smooth muscle cells of blood vessel walls as well as cultured baby hamster kidney cells contain simultaneously two different intermediate-sized filament (IF) proteins, desmin and vimentin. We have examined the question of the occurrence of both proteins in the same IF by chemically crosslinking the single cysteine group present in each of them. Oxidative crosslinking of filaments present in cytoskeletal preparations with cupric ion complexes of 1,10-phenanthroline resulted in formation of three types of dimers: vimentin-vimentin, desmin-desmin, and vimentin-desmin. These dimers were separated by NaDodSO4/polyacrylamide gel electrophoresis and characterized by binding of specific antibodies, by one- and two-dimensional gel electrophoresis of monomers obtained after cleavage of the disulfide bond by thiol agents, and by mapping of radioiodinated tryptic peptides. The demonstration of heterodimers of vimentin and desmin in vascular smooth muscle tissue of cow and chicken and in baby hamster kidney cells shows that the two proteins can be integrated in the same IF and can be nearest neighbors, oriented with their cysteine residues in a mirror-image symmetry. The possible existence of heteropolymer IF in other cell types is discussed.

Regeneration following duplication in imaginal wing disc fragments of Drosophila melanogaster

Fragments from the imaginal wing disc of Drosophila melanogaster were cultured in vivo for periods up to 28 days. One type of edge fragment first duplicated and then ceased to grow, but others often continued to grow following initial duplication and regenerated structures characteristic of other areas of the disc. After 28 days of culture, about 50% of fragments from the presumptive ventral hinge region of the disc grew extensively and produced regenerated as well as original structures. The regenerated structures in some implants were produced at the line of mirror-image symmetry. Regeneration was associated with fragment growth and in many cases was accompanied by loss of duplicate structures. Fragments which were only duplicated after the culture period could in some cases be stimulated to grow by additional culture in fresh hosts, but the results of coculturing two fragments in each host show that culture conditions alone do not control growth and regulation in the fragments. The large, normally regenerating fragment, complementary to the ventral fragment, did not appear to grow following regeneration and only occasionally produced supernumerary structures during prolonged culture. Intact wing discs cultured under similar conditions never produced supernumerary structures. Our results suggest that a duplicated pattern is less stable than a complete, regenerated pattern, which in turn is less stable than an intact disc. We propose that the growth of duplicated disc fragments is stimulated by polarity reversals present at lines of mirror-image symmetry.

Naturally occurring abnormalities (Bruchdreifachbildungen) in the chelae of three species of Crustacea (Decapoda) and a possible explanation

Naturally occurring abnormalities (Bruchdreifachbildungen) in decapod crustacean appendages are described. They are similar to the range of structures experimentally produced by cutting notches in the sides of insect legs (Bohn, 1965). It is argued that they result from failure of wounds to heal. Regeneration from a free surface along the proximodistal axis is always in a distal direction. Surfaces regenerating circumferentially can regenerate in either direction around the circumference. Regeneration will proceed until the two surfaces of the wound meet. Then, where the two surfaces on either side are non-congruent, intervening tissues will be intercalated. This explanation accounts for the range of structures observed after notching experiments (Bohn, 1965) and seen in crustacean Bruchdreifachbildungen. The explanation says that regeneration will occur wherever wounds fail to heal. This avoids the difficulties of the complete circle rule (French, Bryant & Bryant, 1976) and explains why appendages with mirror-image symmetry are often capable of regeneration.