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Biomedical subjects

A W Dorresteijn

Publications and source records attributed to A W Dorresteijn.

7 recordsLinked to original sources
PubMed1998

The site of fertilisation determines dorsoventral polarity but not chirality in the zebra mussel embryo.

The dorsoventral polarity of unequally cleaving spiralian embryos becomes established at an early stage. The factors determining the position of the dorsoventral axis are still unknown. We present data showing that the sperm entry point (SEP) in both normal development and under experimental conditions determines the position of the first cleavage furrow in Dreissena embryos. The position of the spindles at second cleavage is directed by the site of fertilisation also, and the large, dorsal D quadrant of the 4-cell stage always forms opposite the SEP. The spiral chirality at third cleavage seems to be independent of both the fertilisation point and the arrangement of the quadrants. Dextral and sinistral third cleavages are found in a single egg batch, but sinistral cleavages prevail. We postulate that two factors coordinate the proper positioning of the dorsoventral axis. The sperm entry point as an epigenetic factor determines the dorsal side of the embryo. But since the dorsoventral axis forms oblique to the first cleavage furrow, this first decision is still ambiguous, and a second decision is required that, due to the alternative chirality of spiral cleavage, finally sets up the dorsoventral axis.

Animals↗
PubMed1998

Dynamic changes of the microtubule system corresponding to the unequal and spiral cleavage modes in the embryo of the zebra mussel, Dreissena polymorpha (Mollusca, Bivalvia).

Unequal cleavage requires a highly organised cytoskeleton. We investigated the localisation of both tubulins and microtubular arrays in Dreissena eggs during and after fertilisation using confocal laser scanning microscopy. Freshly spawned eggs are arrested in metaphase I. A maternal pool of gamma-tubulin is found mainly in the centre of the asters of the meiotic spindle. The paternal pool of gamma-tubulin, present in the fertilising sperm, could not be traced within the egg, but a microtubule-organising centre forms near the male pronucleus at anaphase II. Male and female pronuclei grow as they migrate in the wake of their aster and rendezvous. First cleavage is unequal and starts without pronuclear fusion. At metaphase the two equal-sized asters span the entire egg in a symmetrical arrangement. At late metaphase the spindle shifts along its longitudinal axis into an eccentric position and the peripheral aster takes on an umbrella-like appearance, whereas the central aster remains spherical. The cleavage furrow becomes determined in the circumferential overlap of the asters. The inequality at second cleavage, however, is due to the unequal size of the asters. The third cleavage spindle also has asymmetrical asters and spindle shift was only observed in the D-cell. The spiral character is a result of an asymmetrical organisation of the larger, vegetal aster. Our results show that the arrangement of the gamma-tubulin clusters and of microtubules changes and develops during early development of Dreissena in a way that can explain the axis-generating asymmetries in cell pattern and the spiral sense of cleavage. The major cytological characters expected to direct pattern formation in this phase of development are: size, position, and symmetry or asymmetry of both spindle and asters.

Animals↗
PubMed1996

Metabolism of oocyte construction and the generation of histospecificity in the cleaving egg. Lessons from nereid annelids.

The growing oocyte and the developing egg of nereid polychaetes are easily accessible to observation and experimental work, a precondition for our research. In preparation for a single semelparous act of reproduction, nereid females reutilize somatic biomass for the synchronized production of numerous oocytes. To keep oogenesis going somatic resources become recycled by the eleocytes and are supplied to the oocytes in form of vitellogenin and nucleotides (among other identified and yet unidentified substances). Both oocytes and eleocytes are free-floating coelomic cells. We postulate that availability of metabolites produced by the eleocytes might suffice to drive synchronous oocyte growth. The cortex of the fully differentiated oocyte contains numerous cortical granules which after fertilization empty by exocytosis thus causing a profound structural reorganization of the zygote cortex. Early development of nereids is extremely constant in time and spatial pattern and from the onset cleavages create diversity among the blastomeres. We have documented a correlation between the quality and amount of cytoplasm, the cell cycle duration and the histogenetic fate of such blastomeres. Experimental change of cytoplasmic proportions of early cleavage cells has serious consequences for axial development. Using a number of differentiation markers we were able to analyze the necessity of certain cleavage steps for the acquisition of the determined state.

Amino Acids↗
PubMed1993

Effects of sodium butyrate on DNA content, glutathione S-transferase activities, cell morphology and growth characteristics of rat liver nonparenchymal epithelial cells in vitro.

The effects of sodium butyrate, which has been shown to act as a differentiation promoting agent in several different tumor cell lines, were studied in a rat liver nonparenchymal epithelial cell line. Exposure of these cells to 3.75 mM butyrate resulted in an inhibition of cell proliferation and, at the same time, an increase in cell diameter (2- to 6-fold) and size of the nuclei (approximately 2-fold) after 3 days in culture. Binucleated cells arose, comprising approximately 12% of the cells investigated, and the number of cells with an abnormal set of chromosomes was increased. Intercellular communication, measured by dye transfer of Lucifer Yellow, was unchanged. From the various xenobiotic metabolizing enzyme activities measured, only those of glutathione S-transferases were significantly altered (increases of 4- to 9-fold) by butyrate treatment. These increases were mainly due to the predominant rise in the pi class isoenzyme which is a well-known tumour marker in rat hepatocarcinogenesis. Thus, our results cannot be interpreted as being either due to promotion of differentiation or due to transformation. The state and type of cell under study has to be considered and investigations of further differentiation parameters are needed to obtain a deeper insight into the biological activity and the underlying mechanisms of cell state modifying agents like butyrate.

Animals↗
PubMed1980

Intercellular communication patterns are involved in cell determination in early molluscan development.

The formation of specialized intercellular junctions, allowing the passage of low-molecular weight regulatory molecules, has been considered as a possible mechanism for regulating embryonic development. No direct evidence for this concept has been found in early development. In the mollusc Pattella vulgata it was demonstrated that cell positioning and specific cellular interactions are key factors in the control of early development. We have now investigated the pattern of intercellular communication during early development of this embryo by intracellular iontophoresis of the fluorescent dye Lucifer Yellow CH. We demonstrate that the formation of regional- and temporal-specific cell-to-cell coupling is correlated with the determination of the mesentoblast--the stem cell of the mesoderm--and the establishment of dorso-ventral polarity.

Animals↗
PubMedDate not supplied

[The effect of aphidicolin on trochoblast differentiation in the early ontogeny of polychaetes].

The differentiation of trochoblasts in Nereis virens and Platynereis dumerlii embryos was investigated during different periods of time after fertilization by means of the DNA replication block. It was shown that the quantal cycle of ciliogenesis is not connected directly with the time of primary trochoblast founder cell formation. Development of the cilia on trochoblasts in P. dumerlii needed normal DNA replication at the fifth cycle. Ciliogenesis in N. virens completely stopped after the inhibition of replication of the fourth cycle and only partly when the fifth and sixth rounds of DNA replication were affected. The data obtained are discussed from the standpoint of Newport and Kirschner's depletion hypothesis.

Animals↗