Morphogenesis in an asymmetric medium

Some key experiments of artificial production ofsitus inversus viscerum are briefly reviewed and a two-step mechanism for the explanation of the systematic asymmetric visceral arrangement in vertebrates is proposed. A two-variable reaction-diffusion system displaying a symmetry-breaking bifurcation is considered, and it is demonstrated that a slight asymmetry of the boundary conditions can give rise to a marked asymmetry in the resulting dissipative structure in both one-and three-dimensional systems. A criterion is formulated allowing classification of reaction-diffusion systems operating in a three-dimensional space with regard to their ability to incorporate slight asymmetries at the boundaries in the form of a chiral dissipative structure.     

The development of asymmetry: the sidedness of drug-induced limb abnormalities is reversed in situs inversus mice

We are studying the development of handedness, in particular the relationships between handed structures with bilateral symmetry, for example the limbs, and those with lateral asymmetry, such as the heart, lungs and gut. Asymmetric (unilateral) developmental limb abnormalities can be induced by chemical treatment of mouse embryos, either in utero by acetazolamide, or in culture by misonidazole. We have examined these effects in mice homozygous for the iv gene. The development of bilateral symmetry in iv/iv mice is normal, but the control of asymmetry appears to be random, that is 50% develop normally (situs solitus), 50% with laterally inverted viscera (situs inversus). We find that the handedness of induced asymmetric limb defects is highly correlated with embryonic visceral situs. Right limb defects are induced in situs solitus embryos, left-sided defects in situs inversus. This suggests that the mechanism of induction of asymmetric defects is not related to any intrinsic difference between the development of left and right limbs, but is connected to visceral asymmetry. In addition, the high correlation of limb defects with situs was observed in culture as well as in utero suggesting that the maternal environment plays no role in the development of asymmetry.     

Random determination of a developmental process: reversal of normal visceral asymmetry in the mouse.

Situs inversus viscerum in the mouse has been shown to be inherited as an autosomal recessive trait (gene symbol iv) with reduced penetrance. It is hypothesized that the normal allele at the iv locus exhibits complete dominance and controls normal visceral asymmetry. Absence of this control allows the situs of visceral asymmetry to be determined in a random fashion. This hypothesis also appears to apply to the inheritance of situs inversus in man and to the experimental production of situs inversus.     

Der Eingeweidesitus beim Alpenmolch (Triturus alpestris) nach Materialdefekten im Ektoderm der Blastula

Zusammenfassung Im Blastulastadium vonTriturus alpestris wurden aus der animalen Hälfte des Keimes rundliche Stücke entnommen, welche aus undeterminiertem Ektoderm bestanden; einige konnten an ihrem vegetativen Rand vielleicht noch ein wenig Mesoderm enthalten. Da die Medianebene in diesen Stadien nicht feststellbar war, ist eine zufallsmäßige Verteilung um die animal-vegetative Achse anzunehmen.Die meisten Embryonen entwickelten sich zu äußerlich normalen Larven. Der Darmsitus von 193 Larven war in 97,9% der Fälle regulär, in 0,5% median und in 1,5% invers. Das entspricht der Inversionsrate nicht operierter Tiere.Mechanische Defekte durch Materialentnahme erzeugten also im Gegensatz zu ähnlichen Defekten im Gastrulastadium keine Eingeweideinversionen. (Bestätigung ähnlicher Ergebnisse v. Kraft's 1969 nach UV-Bestrahlung.) Die sensible Phase für die Erzeugung vonSitus inversus viscerum beginnt nach diesen Beobachtungen im Gastrulastadium.

---

The situs viscerum in the newt (Triturus alpestris) after material defects in the ectoderm of the blastula

Summary In the blastula stage ofTriturus alpestris roundish pieces were removed from the animal half of the embryo, which consisted of undetermined ectoderm; some of them could perhaps contain some mesoderm on their vegetal edge. Since the median plane could not be ascertained in this stage, a chance distribution around the animal-vegetal axis has to be assumed.Most of the embryos developed to externally normal larvae. The gut situs of 193 larvae was regular in 97.9% of the cases, median in 0.5% and inverted in 1.5%. This corresponds to the inversion rate of non operated animals.Therefore mechanic defects by means of removing of material, in contrast to similar defects in the gastrula stage, provoked no gut inversions. (Confirmation of similar results of v. Kraft, 1969 following UV-irradiation). According to these observations the sensible phase for the provocation of situs inversus viscerum begins in the early gastrula stage.

---

---

Ausgeführt mit Unterstützung der Deutschen Forschungsgemeinschaft.     

Adrenergic neurotransmitters and calcium ionophore-induced situs inversus viscerum in Xenopus laevis embryos

Xenopus laevis embryos at the blastula–early tail bud stage were exposed to norepinephrine or octopamine dissolved in culture saline until they reached the larval stage. The left–right asymmetry of the heart and gut was then examined. We found that these adrenergic neurotransmitters induced situs inversus in the heart and/or gut in up to 35% of tested neurula embryos. Norepinephrine-induced situs inversus was blocked by the α-1 adrenergic antagonist prazosin. Furthermore, A23187, a calcium ionophore, also increased the incidence of situs inversus up to 54% when late-neurula embryos were exposed to the solution. A23187 treatment initiated before neural groove formation was less effective. The incidence of situs inversus induced by these reagents decreased towards the control level (2.2%, 25 untreated embryos out of 1127 embryos in total) in embryos past the stage of neural tube closure. In the present experiments we obtained 22 gut-only situs inversus embryos having an inverted gut and a normal heart. In contrast, such embryos were not observed among the 1127 untreated embryos. An adrenergic signal mediated by an increase in intracellular free calcium may be involved in the asymmetrical visceral morphogenesis of Xenopus embryos.     

'ANOVA-simultaneous component analysis (ASCA): a new tool for analyzing designed metabolomics data'

Smilde et al. Bioinformatics (2005), 21(13); 3043–3048 The above paper by Smilde et al. inappropriately quotes results     

Reversed bodies, reversed brains, and (some) reversed behaviors: of zebrafish and men

Although zebrafish with situs inversus show complete reversal of normal visceral and cerebral asymmetries, they show left-right reversal of only some behaviors, with others continuing to show species-typical lateralization. The implication is that, as in humans, there are at least two independent mechanisms for generating asymmetry.     

DE-Cadherin regulates unconventional Myosin ID and Myosin IC in Drosophila left-right asymmetry establishment

In bilateria, positioning and looping of visceral organs requires proper left-right (L/R) asymmetry establishment. Recent work in Drosophila has identified a novel situs inversus gene encoding the unconventional type ID myosin (MyoID). In myoID mutant flies, the L/R axis is inverted, causing reversed looping of organs, such as the gut, spermiduct and genitalia. We have previously shown that MyoID interacts physically with β-Catenin, suggesting a role of the adherens junction in Drosophila L/R asymmetry. Here, we show that DE-Cadherin co-immunoprecipitates with MyoID and is required for MyoID L/R activity. We further demonstrate that MyoIC, a closely related unconventional type I myosin, can antagonize MyoID L/R activity by preventing its binding to adherens junction components, both in vitro and in vivo. Interestingly, DE-Cadherin inhibits MyoIC, providing a protective mechanism to MyoID function. Conditional genetic experiments indicate that DE-Cadherin, MyoIC and MyoID show temporal synchronicity for their function in L/R asymmetry. These data suggest that following MyoID recruitment by β-Catenin at the adherens junction, DE-Cadherin has a twofold effect on Drosophila L/R asymmetry by promoting MyoID activity and repressing that of MyoIC. Interestingly, the product of the vertebrate situs inversus gene inversin also physically interacts with β-Catenin, suggesting that the adherens junction might serve as a conserved platform for determinants to establish L/R asymmetry both in vertebrates and invertebrates.     

Nutrient-patch contrast in relation to clonal integration, with special reference to Glechoma longituba

Patch contrast, defined as the difference between patches, isamong the basic traits of environmental heterogeneity (Kolasa and Pickett 1991;Stuefer 1996). Clonal plants, especially those with long spacers,usually experience certain patches with different nutrient-patchcontrasts (de Kroon et al. 2005; Stuefer 1996). Clonal integrationhas been recognized as a basic strategy, by which clonal plantscan effectively cope with patchy resources and increase theirfitness in such habitats (de Kroon et al. 2005; Zhang et al. 2007).Glechoma longituba is distributed     

Dextrocardia with situs inversus totalis: Cardiovascular surgery in three patients with concomitant coronary artery disease

Three patients with situs inversus totalis (mirror-image dextrocardia) and concomitant coronary artery disease were admitted to our institution for evaluation. In all cases, aortocoronary bypass grafting was successful. Patients with situs inversus and mirror-image dextrocardia are believed to have normal longevity, and, as these studies suggest, they have the same long-term prognosis after coronary bypass grafting as patients with situs solitus.     

Mendel's bequest advanced the understanding of regulatory systems for controlling sugar supply to developing plant embryos

Over the past 15 years, a lot of progress has been made in identifyingand characterizing genes and proteins involved in the transportof photosynthetically produced sugars from leaves to sink organssuch as roots, flowers, and developing seeds. A major step forwardwas the identification and characterization of genes encodingproton sucrose co-transporters of the SUT family (Riesmeier et al., 1992,1993, 1994). Strong evidence suggests that SUTs are responsiblefor the import of sucrose present in the cell wall space ofleaves into the phloem conduit (the phloem or the sieve elementcompanion cell complex, SECCC). Moreover, they appear to beresponsible for the import of sugars into developing seeds (Weber et al., 1997;Matsukura et al., 2000     

Genetical and ultrastructural aspects of the immotile-cilia syndrome.

The immotile-cilia syndrome is a congenital disorder characterized by all cilia in the body being either immotile or showing an ineffective beating pattern. Most symptoms, not unexpectedly, come from the ciliated epithelia, but two further symptoms are: (1) male sterility caused by the spermatozoa being unable to swim progressively (the sperm tail has the same structure as a cilium), and (2) situs inversus in 50% of the cases possible caused by an inability of embryonic cilia to shift the heart to the left side. By electron microscopy, one can see directly which of the many ciliary components is the missing one. The molecular basis of this congenital defect can then be detected, and it has been found to be a heterogeneous disease. There are many genes that, when mutated, will cause the cilia to be dysfunctional or totally immotile. The fact that many genes may be responsible for the syndrome will also explain why it has a relatively high prevalence and why previous investigators have been unable to locate the (assumed single) gene by linkage analysis. The trait, situs inversus, is of particular interest as it occurs in only 50% of the assumed homozygotes. I conclude that the wild-type genes code for a control of the proper body asymmetry and the mutated ones for a lack of control, and, hence, to a random situs determination.     

Molecular basis of left-right asymmetry

In vertebrates visceral asymmetry is conserved along the left-right axis within the body. Only a small percentage of randomization (situs ambiguus), or complete reversal (situs inversus) of normal internal organ position and structural asymmetry is found in humans. A breakdown in left-right asymmetry is occasionally associated with severe malformations of the organs, clearly indicating that the regulated asymmetric patterning could have an evolutionary advantage over allowing random placement of visceral organs. Genetic, molecular and cell transplantation experiments in humans, mice, zebrafish, chick and Xenopus have advanced our understanding of how initiation and establishment of left-right asymmetry occurs in the vertebrate embryo. In particular, the chick embryo has served as an extraordinary animal model to manipulate genes, cells and tissues. This chick model system has enabled us to reveal the genetic pathways that occur during left-right development. Indeed, genes with asymmetric expression domains have been identified and well characterized using the chick as a model system. The present review summarizes the molecular and experimental studies employed to gain a better understanding of left-right asymmetry pattern formation from the first split of symmetry in embryos, to the exhibition of asymmetric morphologies in organs.     

VR-ACS6 is an Auxin-Inducible l-Aminocyclopropane-l-carboxylate Synthase Gene in Mungbean (Vigna radiata)

We have isolated four cDNA clones of ACC synthase from etiolatedmungbean seedlings treated with auxin. PVR-ACS2, pVR-ACS3 andpVR-ACS6 contained the same sequences as the previously reportedDNA fragments, pMAC2, pMAC3 (Botella et al. 1992b) and pMBAl(Kim et al. 1992), respectively. pVR-ACSl was identical withpAIM-1 (Botella et al. 1992a). VR-ACS6 was specifically induced in response to the auxin signal.The IAA-induction of VR-ACS6 was very rapid (within 30 min)and insensitive to cycloheximide treatment at concentrationsup to 100 µM. Significant accumulation of VR-ACS6 mRNAwas detected at 1 µM.IAA.The IAA-induced expression ofVR-ACS6 was suppressed by ABA and ethylene, but enhanced byBA. These characteristics of VR-ACS6 expression were well correlatedwith the physiological data of auxin-induced ethylene productionin mungbean hypocotyls. VR-ACS1 was strongly induced by cycloheximide, but was foundto be not auxin-specific. Inhibitors of either ethylene biosynthesis(AOA) or action (NBD) increased the basal level of VR-ACS1 mRNA. (Received May 7, 1996; Accepted November 25, 1996)     

Genomics of Basal metazoans

An in-depth understanding of the biology of animals will requirethe generation of genomics resources from organisms from allphyla in the metazoan phylogenetic tree. Such resources willideally include complete genome sequences and comprehensiveEST (expressed sequence tag) datasets for each species of interest.Of particular interest in this regard are animals in the earlydiverging non-bilaterian phyla Porifera, Placozoa, Cnidaria,and Ctenophora. Publications describing the results from theuse of genomics approaches in these phyla have only recentlybegun to appear (Kortschak et al., 2003; Yang et al., 2003;Steele et al., 2004). Issues to be considered here include choosingthe basal metazoan species to examine with genomics approaches,the relative advantages and disadvantages of genome sequencingversus EST projects, and the resources and infrastructure requiredto carry out such projects successfully.     

Critical period of rat development when sidedness of asymmetric body structures is determined

We recently reported that rat embryos cultured from the presomite stage in a medium containing the alpha-1 adrenergic agonist, phenylephrine, have a high incidence of situs inversus. In the present study, we have determined more precisely the critical period of development when situs inversus is induced. Rat embryos were harvested at 8 AM on Day 9 of gestation (plug day = Day 0), and divided into different stages of development, namely, early, mid, and late primitive streak stages and early, mid, and late neural plate stages. They then were cultured in rotating bottles to which phenylephrine, 0.5 mM, was added for various durations. After 49 hr of culture, embryos were examined for general morphology including sidedness of the bulboventricular loop, tail, and chorioallantoic placenta. Phenylephrine increased the incidence of situs inversus above control when administered throughout culture from either the early neural plate stage or before, and when administered for 4 hr or more from the early neural plate stage. This increase was significant even at the mid and late primitive streak stages when the control incidence was high. Our results suggest that sidedness of asymmetric body structures is determined during the early neural plate stage. This period is well before the 6-8-somite stage when morphological signs of body asymmetry first appear.     

Axonemal dynein intermediate-chain gene (DNAI1) mutations result in situs inversus and primary ciliary dyskinesia (Kartagener syndrome)

Kartagener syndrome (KS) is a trilogy of symptoms (nasal polyps, bronchiectasis, and situs inversus totalis) that is associated with ultrastructural anomalies of cilia of epithelial cells covering the upper and lower respiratory tracts and spermatozoa flagellae. The axonemal dynein intermediate-chain gene 1 (DNAI1), which has been demonstrated to be responsible for a case of primary ciliary dyskinesia (PCD) without situs inversus, was screened for mutation in a series of 34 patients with KS. We identified compound heterozygous DNAI1 gene defects in three independent patients and in two of their siblings who presented with PCD and situs solitus (i.e., normal position of inner organs). Strikingly, these five patients share one mutant allele (splice defect), which is identical to one of the mutant DNAI1 alleles found in the patient with PCD, reported elsewhere. Finally, this study demonstrates a link between ciliary function and situs determination, since compound mutation heterozygosity in DNAI1 results in PCD with situs solitus or situs inversus (KS).     

Polarotropism and Photomovement of Chloroplasts in the Protonemata of the Ferns Pteris and Adiantum: Evidence for the Possible Lack of Dichroic Phytochrome in Pteris

The actions of red and blue light in the photomovement of chloroplastsand the polarotropic response were studied in the protonemataof the homosporous ferns Pteris vittata L. and Adiantum capillus-venerisL. In Pteris, polarotropism could be induced with blue lightbut not with red light, while both colors of light were effectivein Adiantum protonemata. The photomovement of chloroplasts inthe two species studied by both polarized light and microbeamirradiation, also revealed similar responses to red and bluelight as the polarotropism; i.e. both colors of light were effectivein Adiantum but only blue light was active in Pteris. The resultsin Adiantum were consistent with previous results, which ledto the conclusion that both phytochrome and a blue light-absorbingpigment are involved in the two responses (Kadota et al. 1982,1984, Hayami et al. 1986, Yatsuhashi et al. 1985). By contrast,phytochrome is not involved in either polarotropism or chloroplastmovement in Pteris. Since the phytochrome system is evidentlyactive in every other photoresponses so far investigated inPteris as well as in Adiantum, the present study suggests thata phytochrome system specific to polarotropism and to photomovementof chloroplasts is absent in Pteris. Discussions are presentedon the possible involvement of two phytochrome populations ina fern gametophyte cell and on the possible lack of dichroicphytochrome in Pteris. (Received October 7, 1988; Accepted March 8, 1989)     

Handedness and situs inversus in primary ciliary dyskinesia

...The limbs on the right side are stronger. [The] cause may be ... [that] ... motion, and abilities of moving, are somewhat holpen from the liver, which lieth on the right side. (Sir Francis Bacon, Sylva sylvarum (1627).)Fifty per cent of people with primary ciliary dyskinesia (PCD) (also known as immotile cilia syndrome or Siewert-Kartagener syndrome) have situs inversus, which is thought to result from absent nodal ciliary rotation and failure of normal symmetry breaking. In a study of 88 people with PCD, only 15.2% of 46 individuals with situs inversus, and 14.3% of 42 individuals with situs solitus, were left handed. Because cerebral lateralization is therefore still present, the nodal cilia cannot be the primary mechanism responsible for symmetry breaking in the vertebrate body. Intriguingly, one behavioural lateralization, wearing a wrist-watch on the right wrist, did correlate with situs inversus.