CONTENT - International Society of Zoological Sciences

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ICZ2008 – Abstracts S23 Comparative studies on egg capsules ultrastructure in two species of Tardigrada: Dactylobiotus dispar Murray, 1907 and Isohypsibius granulifer Thulin, 1928. Izabela Poprawa and Magdalena Rost-Roszkowska Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland The eggs of Dactylobiotus dispar and Isohypsibius granulifer, similar to other Tardigrada eggs (Węglarska 1982), are covered with two shells: the vitelline envelope and the chorion. In both cases the vitelline envelope is very thin but the chorion has a multilayered structure. In both analyzed species the chorion is composed of 3 layers: (1) the inner layer of medium electron density; (2) middle, labyrinthine layer; (3) the outer layer of medium electron density. Differences between those two species are connected with all layers thickness and the structure of chorion’s surface. The labyrinthine layer of D. dispar is thinner than the same layer in the chorion of I. granulifer whereas the outer layer is thicker than the outer one of I. granulifer. The chorion surface of D. dispar is covered with small, conical processes with hooked tips. Such processes are not observed on the surface of L. granulifer eggs. Both egg capsules do not possess micropylar opening. Węglarska B. (1982) Ultrastructural study of the formation of egg envelops in Macrobiotus richtersi (Eutardigrada). In. Nelson D.R. (ed.) Proceedings of the third international symposium on the Tardigrada. East Tennessee State University Press, pp. 115-128. Extracellular vacuoles in developing midgut epithelium of Melasoma saliceti (Chrysomelidae, Coleoptera) embryos Magdalena Rost-Roszkowska and Jerzy Klag Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland Embryonic development of Melasoma saliceti lasts 7 days in 22 0 C. Stomodaeum and proctodaeum invaginate at the anterior and posterior ends of the germ band. Together with the ectodermal tissue the endoderm cells also enter into the embryo. The endoderm cells start to migrate over the yolk mass as two lateral bands of cells. On the fifth day of development the endoderm cells spread over the ventral and dorsal sides of the yolk and form the single layered primordium of the midgut epithelium whose cells become connected by specialised intercellular junctions of zonula adherens type. At the same time, between the cells, the intercellular spaces widen in some places. Initially the wide intercellular spaces have irregular outlines, but later they widen, acquire spherical shapes and transform into peculiar extracellular vacuoles. Each vacuole is enclosed within a band of junctional complex. The complexes are formed by zonula adherens, septate and gap junctions. On the sixth day of development the endodermal epithelium cells change shape from flat to cuboidal and eventually into columnar. At the same time, the vacuoles grow and become filled with electron dense content. The cell membranes enclosing the vacuoles form long, densely spaced microvilli eventually filling the vacuole completely. At the beginning of seventh day of development the apical surfaces of the embryonic midgut cells are completely smooth but the extracellular vacuoles come close to the midgut surface. At the end of the seventh day, shortly before hatching the extracellular vacuoles open to the midgut lumen and the microvilli spread over the apical surfaces of the midgut epithelium. Thus in very short time larval midgut, completely covered with fully formed brush-border is formed. The epithelial cells remain connected by zonulae adherentes continuous junctions and gap junctions. The septate junctions are seen only sporadically. The above-presented way of embryonic “preformation” of larval midgut microvilli in a holometobolous insect has not been described. Similar phenomenon of microvilli preformation was observed during differentiation of regenerative cells in some insect species. - 95 - Fine structure of the midgut epithelium of two species belonging to Archaeognatha Lepismachilis notata and Machilis hrabei (Insecta) Magdalena Rost-Roszkowska 1 and Jitka Vilimova 2 1 Department of Animal Histology and Embryology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland 2 Charles University, Faculty of Science, Department of Zoology, 128 44 Praha 2, Vinicna 7, Czech Republic Two primitive wingless insect taxa Archaeognatha and Zygentoma have originally formed one order Thysanura. Later, they were distinguished as two distinct orders Archaeognatha and Zygentoma, the basal taxa of Insecta. Recently some authors have suggested a recovery of the order Thysanura, thus the classification and relationship of Archaeognatha and Zygentoma are not still completely resolved. We analyzed the midgut epithelium and processes of its degeneration and regeneration in Thermobia domestica and Lepisma saccharina, which belong to Zygentoma (Rost 2006). In our present studies we compare the ultrastructure of the midgut epithelium in Lepismachilis notata and Machilis hrabei (Archeognatha) with those of Zygentoma. Midgut epithelium of both archaeognathans Lepismachilis notata and Machilis hrabei is composed of columnar epithelial cells and regenerative cells, which form regenerative cell groups. In both analyzed species the midgut epithelium resembles that of T. domestica and L. saccharina (Zygentoma). The cytoplasm of the epithelial cells shows distinct regionalization in arrangement of organelles, so basal, perinuclear and apical regions are distinguished. The cytoplasm of the regenerative cells is poor in organelles. They are capable of intensive proliferation and differentiation in epithelial ones. The first sign of their differentiation is appearance of cisterns of RER and SER, and numerous mitochondria in their cytoplasm. Rost M.M. 2006. Comparative studies on regeneration of the midgut epithelium in Lepisma saccharina L. and Thermobia domestica Packard (Insecta; Zygentoma). Annals of Entomological Society of America 99: 910-916. Molecular construction of tissues and organs of the Ciona intestinalis larva Nori Satoh Department of Zoology, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan Ascidians, or sea squirts, are sessile marine invertebrate chordates. Although the adult is a filter feeder, the fertilized egg develops quickly into so-called tadpole larva. The larva is composed of only ~2600 cells, which constitute a small number of organs including epidermis, central nervous system (CNS), endoderm and mesenchyme in the trunk, and notochord and muscle in the tail. This represents the most simplified chordate body plan. Specification of ascidian embryonic cells takes place very early at the cleavage stage; developmental fates of epidermis, CNS, endoderm, notochord and muscle are restricted by the 110cell stage. Together with well-characterized lineage of embryonic cells, the ascidian embryo may provide an appropriate experimental system to explore genome-widely the genetic cascades underlying embryonic cell specification. The draft genome of Ciona intestinalis has been decoded in 2002, and its ~120 Mbp euchromatic genome contains ~16,000 protein-coding genes. Among these is a fundamental set of conserved chordate genes encoding transcriptional factors and cell signaling molecules. A thorough examination of Ciona gene expression (the transcriptome) is ongoing, including large-scale EST analyses (~700,000 ESTs), cDNA sequencing, in situ hybridization, and microarray analyses. All of the information is now available with a new Web site of our lab. Here we wish to discuss our current approach using transgenic lines and microarray to disclose genes involved in the formation of the notochord, central nervous system, and muscle of the Ciona larva.
S23 ICZ2008 - Abstracts Organogenesis of digestive organs in vertebrates Sadao Yasugi Faculty of Pharmaceutical Science, Teikyo Heisei University, 2289, Uruido, Ichihara, Chiba 290-0193, Japan The embryonic digestive organs in the vertebrates consist of endodermal epithelium and mesodermal mesenchyme. The former later fulfils functions such as production of digestive enzymes and absorption of nutrients, whereas the latter differentiates into connective tissue layers and smooth muscle layers. It has been well established that interactions between epithelium and mesenchyme are prerequisite for the normal development of the digestive organs. In general, the differentiation of the epithelium requires specific influence of the mesenchyme, and the differentiation of the mesenchyme and its nervous system is regulated by the epithelium. Recent studies carried out in my laboratory have revealed importance of some factors in the mesenchymal and epithelial tissues in the development of the chicken digestive organs, especially the stomach. For example, the determination of regional specificities of the epithelium in the primitive gut is often under the influence of the mesenchymal growth factors such as BMP, FGF and Wnt. On the other hand, the differentiation of the mesenchyme is controlled by sonic hedgehog expressed in the epithelium. The digestive organs possess essentially the same structures among the vertebrates. For example the stomach has glands cells of which produce and secrete digestive enzyme pepsin. The small intestine forms villus structures and epithelial cells produce dissacharidase and absorb nutrients. This means that factors acting in the development of the chicken digestive organs are also active in other vertebrates. In fact, above-mentioned growth actors and sonic hedgehog are known to be expressed in the developing stomach epithelium and mesenchyme of the mammals. Thus roles of these factors elucidated with he chicken embryo must also be important in other vertebrates. - 96 -
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CONTENT - International Society of Zoological Sciences

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