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Biomedical subjects

K Sander

Publications and source records attributed to K Sander.

At least 19 recordsLinked to original sources
PubMed1994

[Dr. Wang's tube--study of a new technique for eliminating pathogens in sperm preparation for reproductive medicine].

A total of 30 ejaculates has been tested for ejaculate volume, spermatozoal concentration, motility, agglomeration, agglutination and contamination by microorganisms. After that the ejaculate has been washed twice and transferred in the Dr. Wangs Tube which was filled with medium before. After an incubation time of 90 minutes very quickly moving spermatozoan could be observed through the microscope in the upper part (C-D) of the Tube. After the Tube was cut by means of a special glasscutter the motility of the containing spermatozoans of part C-D has been determined again, followed by a second bacteriological examination of the so prepared ejaculate. The results of sperm preparation with the Dr. Wangs Tube regarding the sperm motility has been very good (85.7% of the sperm samples showed a motility rate of 90% or even more after treatment). The bacteriological examination has been satisfactory: in 77.7% of the cases all existing sperm bacterias has been eliminated by preparation in the Dr. Wangs Tube. Among other microorganisms Escherichia coli, Proteus mirabilis and Staphylococcus aureus which are considered to be pathologic could be isolated from five of the ejaculates and have been removed after treatment with the Dr. Wangs Tube. The handling of the Tube was rather demanding and Technically problematic. There has been caused glass-splinters by cutting the Tube which got visible while observing the ejaculate-medium-liquid through the microscope. Their sizes were nearly equivalent to the size of a sperms head or even bigger. If the so prepared ejaculate would be used for insemination and in-vitro fertilisation the very small splinters may destroy the success of the treatment and should be avoided or removed. The Dr. Wangs Tube offers a new modified swim-up technique for sperm preparation and is able to produce a high quality, nearly sterile sperm sample. Because of the technical deficiency of the system, the high purchase and running costs and the very small output (sperm sample volume, number of spermatozoans) the Dr. Wangs Tube is not be recommended for the reproductive medicine in its present shape.

Adult↗
PubMed1992

Evolutionary conservation pattern of zinc-finger domains of Drosophila segmentation genes.

A number of genes of the developmental gene hierarchy in Drosophila encode transcription factors containing Cys2His2 zinc finger domains as DNA-binding motifs. To learn more about the evolution of these genes, it is necessary to clone the homologs, or more correctly the orthologs, from different species. Using PCR, we were able to obtain apparently orthologous fragments of hunchback (hb), Krüppel (Kr), and snail (sna) from a variety of arthropods and partly also from other animal phyla. Sequence alignments of these fragments show that the amino acid differences can normally not be correlated with the evolutionary distances of the respective species. This is due to an apparent saturation of potential replacements within the finger domains, which is also evident from the frequent occurrence of convergent replacements. Another recurrent feature of these alignments is that those amino acids that are directly involved in determining the DNA-binding specificity of the fingers are most conserved. Using in vitro bandshift experiments we can indeed show that the binding specificity of a hunchback finger fragment from different species is not changed. This implies that there is a high selective pressure to maintain the regulatory target elements of these genes during evolution.

Amino Acid Sequence↗
PubMed1988

Drosophila nurse cells produce a posterior signal required for embryonic segmentation and polarity.

The segmental pattern of insect embryos depends on influences from morphogenetic centres near each of the egg poles. In Drosophila, maternal effect mutations are known that impair the normal function of each centre. Injection of wild-type cytoplasm into mutant eggs has revealed that morphogenetic signals localized at the anterior and posterior pole of eggs can be transplanted. We show here that these activities can also be detected during oogenesis. Posterior activity can be recovered at an early stage (stage 10, ref. 5) from the oocyte-nurse cell complex, but anterior activity can only be detected in the mature oocytes (stage 14). We conclude that the bicoid-dependent anterior signal, although produced by the nurse cells, does not become active before it is localized to the anterior egg pole, whereas posterior activity can be detected in the nurse cells before, and therefore independently of, its localization to the posterior egg pole.

Animals↗
PubMed1986

The extracellular electrical current pattern and its variability in vitellogenic Drosophila follicles.

We determined the extracellular electrical current pattern around Drosophila follicles at different developmental stages (7-14) with a vibrating probe. At most stages a characteristic pattern can be recognized: current leaves near the oocyte end of the follicle and enters at the nurse cells. Only at late vitellogenic stages was an inward-directed current located at the posterior pole of many follicles. Most striking was the observed heterogeneity both in current pattern and in current density between follicles of the same stage. Different media (changed osmolarity or pH, addition of cytoskeletal inhibitors or juvenile hormone) were tested for their effects on extrafollicular currents. The current density was consistently influenced by the osmolarity of the medium but not by the other parameters tested. Denuded nurse cells (follicular epithelium locally stripped off) show current influx, while an accidentally denuded oocyte produced no current. Our results show that individual follicles may be electrophysiologically different, though their uniform differentiation during vitellogenesis does not reflect such heterogeneity.

Animals↗
PubMed1986

Intracellular electrical potential measurements in Drosophila follicles.

We measured the intracellular electrical potential in oocyte and nurse cells of Drosophila follicles at different developmental stages (6-14) and determined the intrafollicular potential difference. During stages 8-10B, when intrafollicular transport is known to occur, no significant potential difference was found. During late vitellogenic stages the nurse cells assume a more positive potential than the oocyte. This result contrasts with the published data on Hyalophora follicles, in which intercellular electrophoresis of negatively charged proteins occurs from nurse cells to oocyte as a result of an intrafollicular potential difference (nurse cells more negative than the oocyte). Such a potential difference was not observed in Drosophila follicles at any stage, not even after application of juvenile hormone. The extrafollicular electrical field is described with a dipole model. The hypothetical dipole is located in the long axis of the follicle and changes its calculated length stage-specifically.

Action Potentials↗
PubMed1984

Bipartite axiation follows incomplete epiboly in zebrafish embryos treated with chemical teratogens.

Medial clefts in the axis of the trunk region are malformations known from many chordates and are mostly referred to as rachischisis anterior. In teleosts, rachischisis was previously ascribed either to secondary rifting of a single uniform axial rudiment, or to the establishment of two (half) axes and body halves physically separate from the very beginning. In order to decide between these conflicting interpretations, we treated zebrafish embryos during blastodisc stages and epiboly with several chemical teratogens causing rachischisis anterior. Treatment with ethanol, Colcemid, hydroxyurea, or cycloheximide was found to delay the proliferation and movements of the deep cells more strongly than the timing of cell differentiation, so that the deep cells embark on organogenesis before having reached their destinations in the uniform germ shield. Treatment with alpha-amanitin, on the other hand, seems primarily to affect the periblast and enveloping layer; the incomplete epiboly observed in these layers appears to restrain deep cell epiboly physically and thus to cause rachischisis. In both instances, the split condition of the embryo's trunk region is clearly due to the ectopic formation of physically separate body halves right from the beginning, a mode we call bipartite axiation. We also describe secondary anomalies specific for individual teratogens, and briefly discuss the possible origins of rachischisis anterior among other chordates including man.

Abnormalities, Drug-Induced↗
PubMed1980

Embryogenesis in a Drosophila mutant expressing half the normal segment number.

Insect segments are seriated developmental subunits whose borders largely control intra-segmental patterning. The individual segment owes its specific character to position-dependent instructions given to its early embryonic progenitor cells. In Drosophila, the segment borders first become visible as a series of transverse infoldings on the surface of the germ band. We describe here development in a mutant (prdFR1) which forms half the normal number of transverse infoldings spaced at twice the normal distance, thereby subdividing the germ band into a series of giant domains (Fig. 1 a-c). Each domain develops the tracheal pits of two normal segments (Fig. 1e), thus revealing its composite origin, but the larva expresses only one segment border per domain and the cuticle between these borders is similar to the normal segment in both size and zonation (Fig. 2). We conclude that this course of development reflects a conflict between the seriated instructions specifying local segment character (see Fig. 1b) and controlling influences exerted by the abnormally spaced infoldings and later by the definitive segment borders.

Animals↗
PubMed1976

The development of Drosophila embryos after partial u.v. irradiation.

U.v. irradiation of the anterior pole of nuclear multiplication stage Drosophila eggs produces embryos with defective anterior structures. At a low frequency embryos resembling some phenotypes of the bicaudal syndrome of Drosophila were observed. These embryos had no head or thorax and the eight abdominal segments were spread to the anterior of the embryo. Sometimes spiracles, characteristic of the most posterior embryonic segment were observed at the anterior of the embryo. The development of these embryos was followed, and abnormalities occurred as early as blastoderm formation. The extent of the blastoderm defects correlated well with the final abnormality in the embryo.

Animals↗
PubMed1975

Pattern specification in the insect embryo.

Specification of developmental pathways by specific determining substances prelocalized in the egg cytoplasm is duscussed using the so-called germ cell determinants as an example. Some theoretical considerations speak against the assumption that in insects the various elements of the basic body plan are specified by a prelocalized mosaic of specific determinants. Experimental evidence also points towards a largely epigenetic mode of pattern specification. The process of axial pattern specification can be altered drastically by experiment: in some insects, tail ends may be formed in place of head parts and identical wequences of bocy segments may be specified two or even three times along the longitudinal egg axis. The experimental results indicate that polarity and regional character of pattern elements formed are specified by one and the same influence, and that this influence can be shifted to or simulated in various other egg regions by transposition or elimination of egg components, or by UV irradiation. Evidence obtained from several types of experiment in the chironomid midge Smittia points towards a key role for local metabolsim or energy charge in determination of cell polarity and in pattern specification. A model for embryonic pattern specification involving differential reaction of cells to a system of longitudinal gradients, which was proposed in 1960, can in principle formally account for all results described. Some striking coincidences of model and experimental results with Wolpert's concept of positional information are noted. Finally it is pointed out that universality of mechansims for pattern specification is much more likely with respect to formal principles than at the level of their physiological realization.

Animals↗