Blue-green algalike cells associated with the tunic of Ciona intestinalis L.

Summary Certain organisms resembling blue-green algae embedded in the tunic of the solitary ascidian Ciona intestinalis L. are described. Their probable symbiotic role as related to the peculiar habitat of this ascidian is suggested.     

Fluorescent method for studying the morphogenesis and viability of dermatophyte cells

The dermatophyte Microsporum canis is commonly isolated from human and animal infection. The morphogenesis of this fungus was studied during its developmental stages through the fluorescent method Fluorescein Diacetate and Ethidium Bromide. To this end, 50 l dermatophyte suspension were transferred onto cellophane wrapping esterilized discs (2.5 cm of diameter) placed over the surface of Sabouraud dextrose agar on Petri dishes and incubated at 25 °C for 30 days. Every 60 minutes during the first 24 hours and every 12 hours for next 29 days, one disc was transferred onto glass slide, covered with equal volumes of freshly prepared fluorescein diacetate (FDA) and ethidium bromide (EB) solution, mounted with a coverslip and incubated in the dark for 30 minutes, at 25 °C. Each preparation was then examined on a fluorescent microscope. M. canis presented well defined growth stages: (1) tumescence of cells; (2) germination; (3) development of hyphae; (4) production of conidia and (5) tumescence and formation of arthroconidiae. Using the fluorescent method, non viable cells showed a light bright red coloration and viable cells presented green fluorescence. The principal morphological changes have occurred between the 3rd until the 18th day of culture. The method is very useful to demonstrate the dermatophyte growth stages as well as the perfect differentiation between viable and non viable cells.This revised version was published online in October 2005 with corrections to the Cover Date.     

Ascidian tunic cells: morphology and functional diversity of free cells outside the epidermis

Abstract. Tunic cells are free cells distributed in the tunic, the integumentary matrix of tunicates. In ascidians, various types of tunic cells have been described both in solitary and in colonial species. Many of them are functionally specialized and are related to the protection of the animal, such as phagocytosis to prevent infection, acid storage to avoid predation, and pigmentation to protect against solar radiation. While some tunic cells are known to play a role in colonial allorecognition, bioluminescence, and algal symbiosis, the functional roles of many cell types still remain to be determined. The composition of tunic-cell types varies among ascidian species, most likely reflecting the functional requirements of the tunic in each species. Although some cell types, e.g., tunic net cells and tunic bladder cells, are restricted to particular taxa of ascidians, tunic phagocytes are found in all known ascidians. Therefore, tunic phagocytes are hypothesized to be basal and shared with ancestral tunicates. In some ascidians, phagocytic cells are involved in other functions, such as pigmentation, intracellular photosymbiosis, and bioluminescence. These specialized phagocytic cells are hypothesized to be derived from tunic phagocytes, suggesting that tunic cells have a high potential to diversify and evolve a wide variety of cellular functions.     

The geometry of leaf morphogenesis: A theoretical proposition

Plant morphogenesis exhibits numerous bifurcations with particular angle values such as 41°, 53°, which, in lower plants, can be measured in the thallus, and, in higher plants, in the ribs of the leaves. An interpretation of these angles is attempted. Since they characterize the functioning of a morphogenetic field, a formalism was constructed suitable for the study of living systems. The mathematical tool devised here, named the Arithmetical Relator, combines Geometry and Arithmetic, and assumes that a general system results from the interaction between an internal cyclic structure and an environment to which this structure is adapted. The formalism described therefore takes into account partial self-reference and changes in the level of organization. Within this framework, the particular values of the ramification angles are extreme for slight shifts in the internal structure. A pattern of the relations between the genome, the cell and the organ is suggested.

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Résumé La morphogenèse végétale est le siège de nombreuses bifurcations. Celles-ci donnent naissance à des angles particuliers (41°, 53° ...) qui peuvent être mesurés au niveau du thalle des végétaux inférieurs et de la nervation foliaire des végétaux supérieurs. Une interpretation est recherchée: ces angles caractérisant le fonctionnement d'un champ morphogénétique, il a fallu bâtir un formalisme bien adapté au domaine du vivant en vue de cette étude. L'outil mathématique conçu, le Relateur Arithmétique, alliant la géométrie et l'arithmétique, interprète un systéme comme le résultat de l'interaction entre une structure interne cyclique et un environnement auquel elle est adaptée. On pent alors rendre compte d'une auto-référence partielle et d'un changement de niveau d'organisation. Les valeurs particulières des angles de ramification sont extrêmales pour une petite variation de la structure interne du systeme. Une proposition concernant les relations entre génome, cellule et organe est donnée en conclusion.

     

Microtubules and morphogenesis in ordinary epidermal cells ofVigna sinensis leaves

Summary Undifferentiated ordinary epidermal cells (ECs) ofVigna sinensis leaves possess straight anticlinal walls and cortical microtubules (Mts) scattered along them. At an early stage of EC differentiation cortical Mts adjacent to the above walls form bundles normal to the leaf plane, loosely interconnected through the cortical cytoplasm of the internal periclinal wall. At the upper ends of the Mt bundles, Mts fan out towards the external periclinal wall and form radial arrays. Mt bundles and radial arrays exhibit strict alternate disposition between neighbouring ECs. An identical reticulum of cellulose microfibril (CM) bundles is deposited outside the Mt bundles. Local wall pads rise at the junctions of anticlinal walls with the external periclinal one, where the CM bundles terminate. They display radial CMs fanning towards the external periclinal wall. The CM bundles and radial CM systems prevent local cell bulging, but allow it in the intervening wall areas. In particular, the radial CM systems dictate the pattern of EC waviness by favouring local tangential expansion of external periclinal wall. As a result, ECs obtain an undulate appearance. Constrictions in one EC correspond with protrusions of adjacent ECs. ECs affected by colchicine entirely lose their Mts and do not develop wavy walls, an observation substantiating the role of cortical Mts in EC morphogenesis.Abbreviations CM cellulose microfibril - DTT dithiothreitol - EC epidermal cell - MSB microtubule stabilizing buffer - Mt microtubule - PBS phosphate buffered saline - PMSF phenylmethylsulfonyl fluoride     

Apical constriction: A cell shape change that can drive morphogenesis

Biologists have long recognized that dramatic bending of a cell sheet may be driven by even modest shrinking of the apical sides of cells. Cell shape changes and tissue movements like these are at the core of many of the morphogenetic movements that shape animal form during development, driving processes such as gastrulation, tube formation, and neurulation. The mechanisms of such cell shape changes must integrate developmental patterning information in order to spatially and temporally control force production—issues that touch on fundamental aspects of both cell and developmental biology and on birth defects research. How does developmental patterning regulate force-producing mechanisms, and what roles do such mechanisms play in development? Work on apical constriction from multiple systems including Drosophila, Caenorhabditis elegans, sea urchin, Xenopus, chick, and mouse has begun to illuminate these issues. Here, we review this effort to explore the diversity of mechanisms of apical constriction, the diversity of roles that apical constriction plays in development, and the common themes that emerge from comparing systems.     

Leaving the meristem behind: The genetic and molecular control of leaf patterning and morphogenesis

Leaves, which play an essential role in plant photosynthesis, share common features such as being flat structures, but also show an impressive variability in their sizes and shapes. Following its initiation in the meristems, leaf development is patterned along three polarization axes to establish its basic architecture. This process is further complicated in the case of compound leaves with the formation of new growth axes. Growth and differentiation must be properly coordinated to regulate the size and the flatness of the leaf. This review provides an overview of the genetic and molecular regulatory networks underlying leaf development, with an emphasis on leaf polarity and the comparison of simple and compound leaves.     

Chitinases of fungi and plants: their involvement in morphogenesis and host-parasite interaction

Abstract: There has been a considerable amount of recent research aimed at elucidating the roles of chitinase in fungi and plants. In filamentous fungi and yeasts, chitinase is involved integrally in cell wall morphogenesis. Chitinase is also involved in the early events of host-parasite interactions of biotrophic and necrotrophic mycoparasites, entomopathogenic fungi and vesicular arbuscular mycorrhizal fungi. In plants, induction of chitinase and other hydrolytic enzymes is one of a coordinated, often complex and multifaceted defense mechanism triggered in response to phytopathogen attack. Chitinase induction in plants is not considered solely as an antifungal resistance mechanism. Plant chitinases can be induced by various abiotic factors as well and there is some circumstantial evidence to suggest a morphogenetic role despite the apparent absence of the substrate in plant cells. Finally, some chitinases and other chitin-binding proteins including some plant lectins share chitin-binding domains as part of their molecular structure and provide fuel for the so-called 'lectin-chitinase' debate and speculation for the origin of chitinase in plants.     

TRPP2 ion channels: Critical regulators of organ morphogenesis in health and disease

Ion channels control the membrane potential and mediate transport of ions across membranes. Archetypical physiological functions of ion channels include processes such as regulation of neuronal excitability, muscle contraction, or transepithelial ion transport. In that regard, transient receptor potential ion channel polycystin 2 (TRPP2) is remarkable, because it controls complex morphogenetic processes such as the establishment of properly shaped epithelial tubules and left-right-asymmetry of organs. The fascinating question of how an ion channel regulates morphogenesis has since captivated the attention of scientists in different disciplines. Four loosely connected key insights on different levels of biological complexity ranging from protein to whole organism have framed our understanding of TRPP2 physiology: 1) TRPP2 is a non-selective cation channel; 2) TRPP2 is part of a receptor-ion channel complex; 3) TRPP2 localizes to primary cilia; and 4) TRPP2 is required for organ morphogenesis. In this review, we will discuss the current knowledge in these key areas and highlight some of the challenges ahead.     

Hair morphogenesis inAcetabularia mediterranea: Temperature-dependent spacing and models of morphogen waves

Summary Whorls of sterile hairs inA. mediterranea show, at the moment of first appearance of hair initials, a spacing independent of number of hairs in the whorl but dependent on temperature. By changing the temperature at various times before appearance of hair initials, the pattern-forming event can be located at about 3–4 hours before initials become visible.The temperature dependence of spacing is like that of a chemical rate parameter: In (spacing)versus 1/T is linear. This suggests that the spacing is controlled by kinetic rather than structural factors, and correlates well with reaction-diffusion theory.Mathematical analysis and computer simulation have been used to show that the observed sequence of tip-flattening followed by whorl initiation can be interpreted in terms of published models for generation of dissipative structures by reaction and diffusion, and that at least two sequential processes must occur, the first of which shifts growth activity from extremity to circumference of the growing tip, permitting the second to operate around the circumference.Submitted to workshop on Morphogenesis inAcetabularia, Berlin (West), September 1980.     

Appendage morphogenesis in Drosophila: a developmental study of the rotund (rn) gene

Summary The phenotype of rotund (rn) null alleles is described, and compared to wild type. The mutants are expressed zygotically and cause position specific defects in certain imaginal discs (antenna, legs, wing, haltere and proboscis) and their corresponding adult derivatives. In the discs, specific folds are absent in rn mutants compared to wild type. Clonal analysis shows that the rn ⁺ gene is partially autonomous in its expression in cells destined to form certain distal parts of the adult appendages. The results are consistent with the idea that the rn ⁺ gene is required for normal morphogenesis of specific distal parts of the adult appendages.     

Extracellular matrix control of mammary gland morphogenesis and tumorigenesis: insights from imaging

The extracellular matrix (ECM), once thought to solely provide physical support to a tissue, is a key component of a cell’s microenvironment responsible for directing cell fate and maintaining tissue specificity. It stands to reason, then, that changes in the ECM itself or in how signals from the ECM are presented to or interpreted by cells can disrupt tissue organization; the latter is a necessary step for malignant progression. In this review, we elaborate on this concept using the mammary gland as an example. We describe how the ECM directs mammary gland formation and function, and discuss how a cell’s inability to interpret these signals—whether as a result of genetic insults or physicochemical alterations in the ECM—disorganizes the gland and promotes malignancy. By restoring context and forcing cells to properly interpret these native signals, aberrant behavior can be quelled and organization re-established. Traditional imaging approaches have been a key complement to the standard biochemical, molecular, and cell biology approaches used in these studies. Utilizing imaging modalities with enhanced spatial resolution in live tissues may uncover additional means by which the ECM regulates tissue structure, on different length scales, through its pericellular organization (short-scale) and by biasing morphogenic and morphostatic gradients (long-scale). Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Multicellular computer simulation of morphogenesis: blastocoel roof thinning and matrix assembly in Xenopus laevis

In the blastocoel roof (BCR) of the Xenopus laevis embryo, epibolic movements are driven by the radial intercalation of deep cell layers and the coordinate spreading of the overlying superficial cell layer. Thinning of the lateral margins of the BCR by radial intercalation requires fibronectin (FN), which is produced and assembled into fibrils by the inner deep cell layer of the BCR. A cellular automata (CA) computer model was developed to analyze the spatial and temporal movements of BCR cells during epiboly. Simulation parameters were defined based on published data and independent results detailing initial tissue geometry, cell numbers, cell intercalation rates, and migration rates. Hypotheses regarding differential cell adhesion and FN assembly were also considered in setting system parameters. A 2-dimensional model simulation was developed that predicts BCR thinning time of 4.8 h, which closely approximates the time required for the completion of gastrulation in vivo. Additionally, the model predicts a temporal increase in FN matrix assembly that parallels fibrillogenesis in the embryo. The model is capable of independent predictions of cell rearrangements during epiboly, and here was used to predict successfully the lateral dispersion of a patch of cells implanted in the BCR, and increased assembly of FN matrix following inhibition of radial intercalation by N-cadherin over-expression.     

Force and compliance: rethinking morphogenesis in walled cells

In the turgid cells of plants, protists, fungi, and bacteria, walls resist swelling; they also confer shape on the cell. These two functions are not unrelated: cell physiologists have generally agreed that morphogenesis turns on the deformation of existing wall and the deposition of new wall, while turgor pressure produces the work of expansion. In 1990, I summed up consensus in a phrase: "localized compliance with the global force of turgor pressure." My purpose here is to survey the impact of recent discoveries on the traditional conceptual framework. Topics include the recognition of a cytoskeleton in bacteria; the tide of information and insight about budding in yeast; the role of the Spitzenk?rper in hyphal extension; calcium ions and actin dynamics in shaping a tip; and the interplay of protons, expansins and cellulose fibrils in cells of higher plants.     

Wall morphogenesis in diatoms: Deposition of silica by cytoplasmic vesicles

Summary Several TEM and SEM techniques were applied to examine developing structures in valves of the centric diatomThalassiosira eccentrica (Ehrenb.) Cleve after cytokinesis. It was possible to confirm that in each stage of the silicification process there is a distinction between a growing zone with a loose assemblage of silica spheres and a compacting zone in an older phase of development. The spherical structure of the silica in the growing zone results from the addition of silica by small cytoplasmic vesicles of about 300 to 400 Å in diameter. The vesicle membrane fuses with the silicalemma and the vesicle content is released into the silica-deposition vesicle. The origin of these vesicles, named STV, is still unknown.     

Forced to communicate: Integration of mechanical and biochemical signaling in morphogenesis

Morphogenesis is a physical process that requires the generation of mechanical forces to achieve dynamic changes in cell position, tissue shape, and size as well as biochemical signals to coordinate these events. Mechanical forces are also used by the embryo to transmit detailed information across space and detected by target cells, leading to downstream changes in cellular properties and behaviors. Indeed, forces provide signaling information of complementary quality that can both synergize and diversify the functional outputs of biochemical signaling. Here, we discuss recent findings that reveal how mechanical signaling and biochemical signaling are integrated during morphogenesis and the possible context-specific advantages conferred by the interactions between these signaling mechanisms.     

Cytochemical investigations on tunic morphogenesis in the sea peach Halocynthia papillosa (Tunicata, Ascidiacea) 2: demonstration of proteins

In a previous paper, cellulose fibres were demonstrated in the larval, the metamorphosing, and the juvenile tunics. In this paper we used cytochemical methods and X-ray microanalysis to obtain additional information on tunic morphogenesis in Halocynthia papillosa. The chemical composition of the tunic evolves with its structural complexity. The larval and juvenile fibres are shown to be structurally and chemically different. While neither proteins nor glycosaminoglycans seem to be associated with the larval fibres, the juvenile fibres consist of a cellulose core wrapped in a sheath of tannophilic proteins. Patches of glycosaminoglycans line their longitudinal axes. In the course of metamorphosis, the cuticle undergoes profound modifications in regions of spine morphogenesis. Granular material that was previously called fibro-granular material (Lübbering et al., 1993) is essential to the formation of cuticular plates and spines. During metamorphosis, this material accumulates in epidermal granules and is discharged into the tunic. It crosses the fundamental layer of the tunic and reaches the cuticle. Our results strongly suggest that this material consists of proteins rich in cysteine and hydrophobic amino acids.     

早期形态发生:一种解决贻贝科(软体动物门:双壳纲)分类、系统发育和进化问题的方法

作者对贻贝科贝类的幼虫和幼贝期发育阶段形态结构的出现和变化顺序进行了研究,其约60个不同分类单元的个体发生可归纳为4种形态发生类型或模式。主要对3个形态发生区域的阶段形态结构的起源、发育变化和同源性做了研究。其一,即中央区域,开始形成于前双壳Ⅰ期(PD-Ⅰ),在某个分类单元它可以在前双壳Ⅱ期(PD-Ⅱ)和幼贝期(N)形成,而在其它分类单元则在前双壳Ⅱ期、幼贝期和双壳期(D)形成;第二区域,即背部后区,在幼贝期出现;第三区域,即背部前区,出现于双壳期。双壳期背部后区在某个分类单元起源于幼贝期的形态构造,在其它分类单元则可能起源于双壳期的形态构造。与在贻贝分类学上应用的成体特征相比,早期发育阶段中央和背部后区的形态结构显示出很明显的发育顺序或特征变化规律。根据以前人们熟知而尚未应用到分类和系统发育研究中的早期发育阶段形态特征,作者重新修订了Soot-Ryen的现生贻贝科种上阶元分类系统,重新提出了科内系统发育关系。修订的分类系统表明,Scarlato and Starobogatov(1984)提出的贻贝科各亚科由偏顶蛤亚科开始,沿4条系统发育路线演化发展,对应其早期发育阶段的4类形态发生类型或模式。