CONTENT - International Society of Zoological Sciences

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.
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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.