MASISH: a database for gene expression in maize seeds

Grass seeds are complex organs composed by multiple tissues and cell types that develop coordinately to produce a viable embryo. The identification of genes involved in seed development is of great interest, but systematic spatial analyses of gene expression on maize seeds at the cell level have not yet been performed. MASISH is an online database holding information for gene expression spatial patterns in maize seeds based on in situ hybridization experiments. The web-based query interface allows the execution of gene queries and provides hybridization images, published references and information of the analyzed genes. AVAILABILITY: http://masish.uab.cat/.     

Ephrin-Eph signaling in embryonic tissue separation

The physical separation of the embryonic regions that give rise to the tissues and organs of multicellular organisms is a fundamental aspect of morphogenesis. Pioneer experiments by Holtfreter had shown that embryonic cells can sort based on “tissue affinities,” which have long been considered to rely on differences in cell-cell adhesion. However, vertebrate embryonic tissues also express a variety of cell surface cues, in particular ephrins and Eph receptors, and there is now firm evidence that these molecules are systematically used to induce local repulsion at contacts between different cell types, efficiently preventing mixing of adjacent cell populations.     

Comparative ultrastructure of adhesive systems in the turbellaria

Summary Glandular adhesive organs and other structures by which turbellarians attach themselves temporarily to surfaces have been studied by electron microscopy. Adhesive organs in representatives of the turbellarian orders Haplopharyngida, Macrostomida, Polycladida, Rhabdocoela, Proseriata, and Tricladida are composed of three cell types: two gland cell types and a modified epidermal cell type through which the necks of the glands project. One of the gland types is characterized by its dense membrane-bound, 0.2–0.7Μm diameter, secretion granules and is called here theviscid gland on the basis of evidence that it secretes the adhesive substance by which the organs attach to surfaces. The other gland type is characterized by smaller (0.1Μm), less-dense, membrane-bound secretion granules and is called thereleasing gland on the basis of evidence that it secretes a substance by which adhering organs are released from surfaces. The modified epidermal cell is called theanchor cell; it has a well-developed cell web and bears microvilli with fibrous cores surrounding the tips of the gland necks in a collar-like fashion. Adhesive organs that have the two gland types, viscid and releasing glands, are referred to here asduo-gland adhesive organs. Other turbellarians, including orders Nemertodermatida, Acoela, and Lecithoepitheliata, have adhesive glands or other adhesive structures with a morphology unlike that of duo-gland adhesive organs. Ultrastructural characters of the adhesive organs show that the Macrostomida and Haplopharyngida are related, and that the Polycladida, Rhabdocoela, Proseriata, and Tricladida are related, and that these two groups of orders share a common ancestor. The Nemertodermatida, Acoela, and Lecithoepitheliata, with morphologically different adhesive systems, are apparently derived separately from these orders.     

Establishment of polarity in lateral organs of plants

BACKGROUND: Asymmetric development of plant lateral organs initiates by partitioning of organ primordia into distinct domains along their adaxial/abaxial axis. A recent model proposes that a meristem-born signal, acting in a concentration-dependent manner, differentially activates PHABULOSA-like genes, which in turn suppress abaxial-promoting factors. As yet, no abaxial factors have been identified that when compromised give rise to adaxialized organs. RESULTS: Single mutants in either of the closely related genes KANADI1 (KAN1) or KANADI2 (KAN2) have little or no effect on plant morphology. However, in kan1 kan2 double mutant plants, there is a replacement of abaxial cell types by adaxial ones in most lateral organs. The alterations in polarity establishment are associated with expansion in the expression domain of the PHB-like genes and reduction in the expression of the previously described abaxial-promoting YABBY genes. Ectopic expression of either of the KANADI genes throughout leaf primordia results in dramatic transformation of adaxial cell types into abaxial ones, failure of lateral blade expansion, and vascular tissue formation. CONCLUSION: The phenotypes of KANADI loss- and gain-of-function alleles suggest that fine regulation of these genes is at the core of polarity establishment. As such, they are likely to be targets of the PHB-mediated meristem-born signaling that patterns lateral organ primordia. PHB-like genes and the abaxial-promoting KANADI and YABBY genes appear to be expressed throughout primordia anlagen before becoming confined to their corresponding domains as primordia arise. This suggests that the establishment of polarity in plant lateral organs occurs via mutual repression interactions between ab/ad factors after primordium emergence, consistent with the results of classical dissection experiments.     

The neural tube/notochord complex is necessary for vertebral but not limb and body wall striated muscle differentiation.

The aim of this work was to investigate the role played by the axial organs, neural tube and notochord, on the differentiation of muscle cells from the somites in the avian embryo. Two of us have previously shown that neuralectomy and notochordectomy is followed by necrosis of the somites and consecutive absence of vertebrae and of most muscle cells derived from the myotomes while the limbs develop normally with muscles. Here we have focused our attention on muscle cell differentiation by using the 13F4 mAb that recognizes a cytoplasmic antigen specific of all types of muscle cells. We show that differentiation of muscle cells of myotomes can occur in the absence of notochord and neural tube provided that the somites from which they are derived have been in contact with the axial organs for a defined period of time, about 10 hours for the first somites formed at the cervical level, a duration that progressively reduces caudalward (i.e. for thoracic and lumbar somites). Either one or the other of the two axial organs, the neural tube or the notochord can prevent somitic cell death and fulfill the requirements for myotomal muscle cell differentiation. Separation of the neural tube/notochord complex from the somites by a surgical slit on one side of the embryo gave the same results as extirpation of these organs and provided a perfect control on the non-operated side. A striking finding was that limb and body wall muscles, although derived from the somites, differentiated in the absence of the axial organs. However, limb muscles that develop after excision of the neural tube started to degenerate from E10 onward due to lack of innervation. In vitro explantation of somites from different axial levels confirmed and defined precisely the chronology of muscle cell commitment in the myotomes as revealed by the in vivo experiments.     

The potential role of exosomes in the diagnosis and therapy of ischemic diseases

In the past, exosomes have been thought of as cellular dust. Today, they are thought to be carriers of real biomarkers and intercellular biological information. The composition of exosomes differs according to their source, and the subsequent information they carry, such as protein, microRNA or mRNA, may also be different. Recent studies have demonstrated that exosomes in ischemic diseases can help to make an early diagnosis, and in cellular experiments and animal models, exosomes promote angiogenesis, restrain cell apoptosis and reduce inflammation, among other actions, to protect ischemic organs. There is evidence that these protective effects are related to microRNAs in exosomes. In this review, we discuss the use of exosomes for early diagnosis of ischemic diseases and recent advances in the therapeutic use of exosomes in cell and mammalian models of ischemic diseases.     

Intrinsic and extrinsic control of growth in developing organs

The growth rate and final size of developing organs is controlled by organ-intrinsic mechanisms as well as by hormones and growth factors that originate outside the target organ. Recent work on Drosophila imagined discs and other regenerating systems has led to the conclusion that the intrinsic growth-control mechanism that controls regenerative growth depends on position-specific interactions between cells and their neighbors, and that these interactions also control pattern formation. According to this interpretation, local growth by cell proliferation is stimulated when cells with disparate positional information are confronted as a result of grafting or wound healing. This local growth leads to intercalation of cells with intervening positional values until the positional information discontinuity is eliminated. When all discontinuities have been eliminated from a positional field, growth stops. In this article we consider the possibility that organ growth during normal development may be controlled by an intercalation mechanism similar to that proposed for regenerative growth. Studies of imaginal disc growth are consistent with this suggestion, and in addition they show that the cell interactions thought to control growth are independent of cell lineage. Developing organs of vertebrates also show intrinsic growth-control mechanisms, as demonstrated by the execution of normal growth programs by immature organs that are transplanted to fully grown hosts or to hosts with genetically different growth parameters. Furthermore, these organ-intrinsic mechanisms also appear to be based on position-specific cell interactions, as suggested by the growth stimulation seen after partial extirpation or rearrangement by grafting. In organs of most adult vertebrates, the organ-intrinsic growth-control system seems to be suppressed as shown by the loss of regenerative ability, although it is clearly retained in the limbs, tails and other organs of salamanders. The clearest example of an extrinsic growth regulator is growth hormone, which plays a dominant role along with insulin-like growth factors, thyroid hormone and sex hormones in supporting the growth of bones and other organs in postnatal mammals. These hormones do not appear to regulate prenatal growth, but other hormones and insulin-like growth factors may be important prenatally. The importance of other growth factors in regulating organ growth in vivo remains to be established. It is argued that both intrinsic and extrinsic factors control organ growth, and that there may be important interactions between the two types of control during development.     

Neuronal diversity in the retina

The listing of cell types present in the retina is nearing completion, the first time this can be said for any significantly complex sample of the central nervous system. Mammalian retinas contain approximately 55 separate neuronal types. The functions of 22 of them are known or can be strongly inferred. For these 22, in every instance, a cell defined as a 'type' by structural criteria carries out a distinct and individual physiological function. Electrophysiological experiments continue to reveal new features of the retina's handling of information, and there is every reason to believe that the remaining 33 types of cell will also have distinct physiological functions. Further subtleties clearly exist in both peripheral and central visual coding.     

Adhesive organs of the gastrotricha

Summary Adhesive organs of 17 gastrotrich species of the order Macrodasyida and 2 species of the order Chaetonotida (Chaetonotida-Paucitubulatina) can be seen by transmission electron microscopy to comprise two gland cell types. These cells are morphologically similar to viscid and releasing glands of the Turbellaria and so are identified by these same names; the adhesive system in these gastrotrichs is therefore called a duo-gland system considered at least functionally comparable to the duo-gland organs of turbellarians. The two gland cell types project their necks through tubiform extensions of the animal's cuticle. Some adhesive tubules have only one of each gland type; others, even in the same species, may have two viscid and one releasing glands; and compound organs such as posterior footlike appendages may have three and four viscid glands and one releasing gland per tubule. Gland cells in some species have fibers, evidently cytoskeletal in function. The adhesive tubules are quite similar in all of these species and provide few characters for determining within-group relationships of the gastrotrichs. The duo-gland system of the Gastrotricha is probably not homologous with that of the Turbellaria.Abbreviations Used in Figures cu cuticle - ep epidermal cell - f fiber - la lateral adhesive organ - m muscle - pa posterior adhesive organ - rg releasing gland - sc sensory cilium - scb sensory cell body - vg viscid gland This research was supported by NSF grants DEB-77-06058 (S. Tyler, P.I.) and GB 42211 (R.M. Rieger, P.I.)     

Anti-herbivore structures of Paulownia tomentosa: morphology, distribution, chemical constituents and changes during shoot and leaf development

Background and Aims: Recent studies have shown that small structures on plant surfacesserve ecological functions such as resistance against herbivores.The morphology, distribution, chemical composition and changesduring shoot and leaf development of such small structures wereexamined on Paulownia tomentosa. Methods: The morphology and distribution of the structures were studiedunder light microscopy, and their chemical composition was analysedusing thin-layer chromatography and high-performance liquidchromatography. To further investigate the function of thesestructures, several simple field experiments and observationswere also conducted. Key Results: Three types of small structures on P. tomentosa were investigated:bowl-shaped organs, glandular hairs and dendritic trichomes.The bowl-shaped organs were densely aggregated on the leavesnear flower buds and were determined to be extrafloral nectarines(EFNs) that secrete sugar and attract ants. Nectar productionof these organs was increased by artificial damage to the leaves,suggesting an anti-herbivore function through symbiosis withants. Glandular hairs were found on the surfaces of young and/orreproductive organs. Glandular hairs on leaves, stems and flowerssecreted mucilage containing glycerides and trapped small insects.Secretions from glandular hairs on flowers and immature fruitscontained flavonoids, which may provide protection against someherbivores. Yellow dendritic trichomes on the adaxial side ofleaves also contained flavonoids identical to those secretedby the glandular hairs on fruits and flowers. Three specialtypes of leaves, which differed from the standard leaves inshape, size and identity of small structures, developed nearyoung shoot tips or young flower buds. The density of smallstructures on these leaf types was higher than on standard leaves,suggesting that these leaf types may be specialized to protectyoung leaves or reproductive organs. Changes in the small structuresduring leaf development suggested that leaves of P. tomentosaare primarily protected by glandular hairs and dendritic trichomesat young stages and by the EFNs at mature stages. Conclusions: The results indicate that P. tomentosa protects young and/orreproductive organs from herbivores through the distributionand allocation of small structures, the nature of which dependson the developmental stage of leaves and shoots.     

ADF proteins are involved in the control of flowering and regulate F-actin organization, cell expansion, and organ growth in Arabidopsis

Based mostly on the results of in vitro experiments, ADF (actin-depolymerizing factor) proteins are thought to be key modulators of the dynamic organization of the actin cytoskeleton. The few studies concerned with the in vivo function of ADF proteins that have been reported to date were performed almost exclusively using single-cell systems and have failed to produce consistent results. To investigate ADF functions in vivo and during the development of multicellular organs, we generated transgenic Arabidopsis plants that express a cDNA encoding an ADF protein (AtADF1) in the sense or the antisense orientation under the control of a strong constitutively active promoter. Selected lines with significantly altered levels of AtADF protein expression were characterized phenotypically. Overexpression of AtADF1 resulted in the disappearance of thick actin cables in different cell types, caused irregular cellular and tissue morphogenesis, and reduced the growth of cells and organs. In contrast, reduced AtADF expression promoted the formation of actin cables, resulted in a delay in flowering, and stimulated cell expansion as well as organ growth. These results are consistent with the molecular functions of ADF as predicted by in vitro studies, support the global roles of ADF proteins during the development of a multicellular organism, and demonstrate that these proteins are key regulators of F-actin organization, flowering, and cell and organ expansion in Arabidopsis.     

The organization of ampullary sense organs in the electric fish, Gymnarchus niloticus

Three types (A, B, and C) of ampullary sense organs occur in the skin of Gymnarchus niloticus. In type A the ampulla is connected to the surface of the skin by an open duct whereas in B and C organs it is closed, though overlain by specialized epidermal cells. In each case the receptor cell surface in contact with the ampullary lumen bears microvilli; these are more highly developed in B and C organs than in type A. Fine structural observations are consistent with the view that the organs are electric receptors of three different types.     

The leukocytic organ of the megascolecid earthworm,Amynthas diffringens (annelida,oligochaeta)

Leukocytic organs of Amynthas diffringens are aggregations of leukocytes contained within a smooth muscle and stromal cell framework suspended in the coelom. Elongate processes of stromal cells subdivide each organ into numerous cell-filled compartments and are perforated by 130-nm pores that may permit the exchange of humoral substances between compartments, or between the organ and the surrounding coelomic fluid. We divide leukocytes within the organs into four morphotypes. Phagocytic leukocytes have many lysosomelike vesicles and may possess phagosomes. Mature types I, II, and III granulocytic leukocytes share certain features but are readily distinguished by cell shape and by the size, shape, and electron density of the cytoplasmic inclusions. Immature as well as mature phagocytes and granulocytes occur within these organs, suggesting that they are sites of leukocyte maturation and storage. Concentrations of leukocytes within the organs result in extensive cell to cell contact, especially within islets and tightly packed cords. Phagocytosis of cell debris occurs throughout the organs. Immature stages of the four morphotypes are difficult to distinguish even at high magnification, raising the possibility that they may originate from a common precursor. Our inability to observe mitoses or to detect lymphocytelike stem cells suggests that immature leukocytes migrate to the organs via coelomic fluid from as yet unidentified primary sites of production.     

Why don't we get more cancer? A proposed role of the microenvironment in restraining cancer progression

Tumors are like new organs and are made of multiple cell types and components. The tumor competes with the normal microenvironment to overcome antitumorigenic pressures. Before that battle is won, the tumor may exist within the organ unnoticed by the host, referred to as 'occult cancer'. We review how normal tissue homeostasis and architecture inhibit progression of cancer and how changes in the microenvironment can shift the balance of these signals to the procancerous state. We also include a discussion of how this information is being tailored for clinical use.     

Proteomic dissection of plant development

Plant development is controlled by complex endogenous genetic programs and responses to environmental cues. Proteome analyses have recently been introduced to plant biology to identify proteins instrumental in these developmental processes. To date most plant proteome studies have been employed to generate reference maps of the most abundant soluble proteins of plant organs at a defined developmental stage. However, proteomics is now also utilized for genetic studies comparing the proteomes of different plant genotypes, for physiological studies analyzing the influences of exogenous signals on a particular plant organ, and developmental studies investigating proteome changes during development. Technical advances are now beginning to allow a proteomic dissection of individual cell types, thus greatly increasing the information revealed by proteome analyses.     

Immunohistochemical and ultrastructural studies on ciliary sense organs of arrow worms (Chaetognatha)

We examined epibenthic and pelagic species of Chaetognatha (Spadellidae and Sagittidae) using immunohistofluorescence and confocal laser scanning microscopy to detect tubulin and cell nuclei in whole-mount preparations and scanning and transmission electron microscopy to visualize the ultrastructural organisation of their ciliary sense organs. All chaetognaths bear three types of ciliary sense organs distributed throughout the body: (1) transversally oriented ciliary fence organs, (2) longitudinally (parallel to the anterior-posterior axis) oriented ciliary tuft organs, and (3) a ciliary loop, the corona ciliata. This study targets the ciliary fence as well as the ciliary tuft organs. Two types of primary receptor cells constitute the ciliary fence and ciliary tuft organs. The first type of receptor cells forms a single cell line along the midline axis of the organs, whereas the second type of receptor cells forms multiple lines of cells at either side of type 1 cells. Each receptor cell extends a single, non-locomotory cilium from its narrow apex collared by slender, non-reinforced microvilli; however, both types of sensory cells considerably differ on ultrastructural level. Type 1 sensory cells have thicker cilia than those protruded by the type 2 sensory cells which are characterized by rootlets consisting of an elongated, amorphous distal as well as a cross-striated proximal portion. These results likely reveal that both types of sensory cells have distinct functions.     

Markers for hypersensitive response and senescence show distinct patterns of expression

Controlled cellular suicide is an important process that can be observed in various organs during plant development. From the generation of proper sexual organs in monoecious plants to the hypersensitive response (HR) that occurs during incompatible pathogen interactions, programmed cell death (PCD) can be readily observed. Although several biochemical and morphological parameters have been described for various types of cell death in plants, the relationships existing between those different types of PCD events remain unclear. In this work, we set out to examine if two early molecular markers of HR cell death (HIN1 and HSR203J) as well as a senescence marker (SAG12) are coordinately induced during these processes. Our result indicates that although there is evidence of some cross-talk between both cell death pathways, spatial and temporal characteristics of activation for these markers during hypersensitive response and senescence are distinct. These observations indicate that these markers are relatively specific for different cell death programs. Interestingly, they also revealed that a senescence-like process seems to be triggered at the periphery of the HR necrotic lesion. This suggests that cells committed to die during the HR might release a signal able to induce senescence in the neighboring cells. This phenomenon could correspond to the establishment of a second barrier against pathogens. Lastly, we used those cell death markers to better characterize cell death induced by copper and we showed that this abiotic induced cell death presents similarities with HR cell death.     

Haemopoietic organs and effect of their ablation on total haemocyte count in lemon-butterfly,Papilio demoleus L

The haemopoietic organs in Vth instar larvae of P. demoleus are in the form of thin transparent cellular sheets, closely wrapped around the base of each wing-pad. Three cell types viz; prohaemocytes, plasmatocytes and oenocytoids appear to be derived from these organs and their ablation caused a reduction in cell number which, in turn, revealed that the haemocytes in general are derived both from the haemopoietic organs as well as from the circulating blood cells.