Characterization of three synuclein genes in Xenopus laevis.

The synuclein family consists of three small intracellular proteins mainly expressed in neural tissues, and has been associated with human neurodegenerative diseases. We have examined the spatial and temporal expression patterns of three synuclein genes during embryogenesis of Xenopus laevis. The Xenopus synucleins were firstly expressed in the developing nervous system at the tail bud stages.

Xenopus X-box binding protein 1, a leucine zipper transcription factor, is involved in the BMP signaling pathway.

We describe a novel basic leucine zipper transcription factor, XXBP-1, which interacts with BMP-4 in a positive feedback loop. It is a maternal factor and is zygotically expressed in the dorsal blastopore lip and ventral ectoderm with the exception of the prospective neural plate during gastrulation. Overexpression of XXBP-1 leads to ventralization of early embryos as described for BMP-4, and inhibits neuralization of dissociated ectoderm.

Four decades of teaching developmental biology in Germany.

I have taught developmental biology in Essen for 30 years. Since my department is named Zoophysiologie (Zoophysiology), besides Developmental Biology, I also have to teach General Animal Physiology. This explains why the time for teaching developmental biology is restricted to a lecture course, a laboratory course and several seminar courses.

XETOR regulates the size of the proneural domain during primary neurogenesis in Xenopus laevis.

The interaction between early proneural genes and lateral inhibition determines the number of primary neurons. The mechanism for regulating the size of the proneural domain, however, has not been clarified. We show here that inhibition of the function of XETOR in Xenopus, a homolog of human oncoprotein ETO/MTG8, leads to a neurogenic phenotype of expanded proneural domain without alteration in the density of primary neurons.

Determination, induction and pattern formation in early amphibian embryos.

Determination (inducing) factors, the extracellular matrix, signaling pathways, transcription factors and genes interact in pattern formation and neural induction. Genes can either be activated or repressed. The animalvegetal and dorso-ventral polarities are determined in very early developmental stages.

Basic fibroblast growth factor can induce exclusively neural tissue in Triturus ectoderm explants.

Ectoderm was isolated from early gastrulae of Triturus alpestris and induced with recombinant basic fibroblast growth factor (b-FGF). Neural tissue differentiated in about 38% of the explants which were induced by 2,5 μg/ml FGF. These explants do not contain other tissues, or contain only small amounts of mesenchyme and melanophores which are probably derived from induced neural crest.

Urea is Necessary for the Culture of Embryos of the Marsupial Frog Gastrotheca riobambae, and is Tolerated by Embryos of the Aquatic Frog Xenopus laevis: (ureotelism/urea concentration in frog blood/culture of frog embryos/mesoderm induction).

Urea was found in the capsular fluid that bathes Gastrotheca riobambae embryos during incubation in the maternal pouch. The urea concentration in this fluid is higher than in blood from the mother, indicating that urea is accumulated by the embryo during the period of maternal incubation. Gastrotheca tadpoles tolerate up to 500 mM urea with 86% survival after 24 hours and die in solutions of 0.

The Dorsalization of Spermann's Organizer Takes Place during Gastrulation in Xenopus laevis Embryos: (Spemann's organizer/dorsal mesoderm/neural induction/suramin/inhibition of notochord formation).

Suramin, a polyanionic compound, which is thought to inhibit the binding of growth factors to their receptors, prevents the differentiation of the dorsal blastopore lip of early gastrulae into dorsal mesodermal structures as notochord and somites. Suramin treated blastopore lips form ventral mesodermal structures, mainly heart structures. Several cases showed rythmic contractions ("beating hearts").

Spatial and temporal localization of FGF receptors in Xenopus laevis.

Mesoderm formation is a result of cell-cell interactions between the vegetal and animal hemisphere and is thought to be mediated by inducing peptide growth factors including members of the FGF and TGFβ superfamilies. Our immunochemical study analyses the distribution of FGF receptors coded by the human flg gene during embryogenesis of Xenopus laevis. Immunostaining was detected in the dorsal and ventral ectoderm and also in the marginal zone of early cleavage, blastula and gastrula stages.

Homoiogenetic Neural Inducing Activity of the Presumptive Neural Plate of Xenopus Laevis: (Xenopus laevis/neural induction/homoiogenetic induction/heteroplastic transplantation/Xenopus borealis).

Heteroplastic combinations were made between Xenopus laevis presumptive neural plate and competent ectoderm of Xenopus borealis. Primarily induced presumptive neural plate cells (Xenopus laevis) can easily be distinguished from Xenopus borealis cells by specific quinacrine fluorescence of the nuclei. It was clearly shown that presumptive neural plate, which has primarily been induced by the underlying chordamesoderm exerts homoiogenetic inducing activity on competent ectoderm.

A mesoderm-inducing factor from a Xenopus laevis cell line : Chemical properties and relation to the vegetalizing factor from chicken embryos.

We have compared the chemical properties and biological activities of the mesoderm-inducing factor that is secreted by the Xenopus XTC cell line with the vegetalizing factor from chicken embryos. The inducing activity of the factors was tested in different concentrations on totipotent ectoderm either by implantation into early gastrulae of Triturm alpestris or by application of solutions to isolated ectoderm of early gastrulae of Xenopus laevis. Both factors have similar properties.

Crystallins during Xenopus laevis free lens formation.

The ontogeny and localization of crystallins during free lens development (i.e. lens development without the optic vesicle) were investigated in Xenopus laevis using the indirect immunofluorescence staining method with an antiserum raised against homologous total lens soluble proteins.

Binding of anti-fibronectin to early amphibian ectoderm does not result in inhibition of neural induction under in vitro conditions.

Antibodies directed to fibronectin (anti-FN) were injected into the blastocoel of late blastulae of Xenopus laevis. Two animal caps (ectoderm) were isolated, when control embryos reached the early gastrula stage, and were combined with untreated upper blastopore lip in the sandwich method. In two control series fibronectin or Holtfreter solution was injected into the blastocoel.

The inducing capacity of the presumptive endoderm of Xenopus laevis studied by transfilter experiments.

The inducing capacity of the vegetal hemisphere of early amphibian blastulae was studied by placing a Nucleopore filter (pore size 0.4 μm) between isolated presumptive endoderm and animal (ectodermal) caps. The inducing effect was shown to traverse the Nucleopore membrane.

The activation of a neuralizing factor in the neural plate is correlated with its homoiogenetic-inducing activity.

Neural plates which are induced in the dorsal ectoderm of Triturus by the underlying mesoderm acquire, in turn, neural-inducing activity. This process is correlated with the appearance of neural-inducing activity in the microsomal fraction of the neural plate homogenate. The high-speed supernatant also acquires inducing activity after neural induction, but to a lesser extent.

Electron microscope study of the binding of Con A-gold to superficial and inner ectoderm layers ofXenopus laevis and its relation to the neural-inducing activity of this lectin.

Isolated competent amphibian ectoderm differentiates into neural (archencephalic) structures when treated with the plant lectin concanavalin A (Con A). While the inner ectoderm layer ofXenopus laevis forms brain structures after incubation with Con A, the outer ectoderm layer differentiates into ciliated epidermis only. This difference can be correlated with the pattern of Con A bound to the plasma membrane.

Change in the differentiation pattern ofXenopus laevis ectoderm by variation of the incubation time and concentration of vegetalizing factor.

Early amphibian gastrula ectoderm (Xenopus laevis) has been treated with vegetalizing factor using the sandwich technique, varying the period of incubation and the inducer concentration.The pattern of induced tissues depends on three factors: the inducer concentration, the size of inducer pellet and the time of exposure of ectodermal target cells to inducer.Short treatment with inducer will result in the formation of blood cells and heart structures.

Biological activity of the vegetalizing factor: Decrease after coupling to polysaccharide matrix and enzymatic recovery of active factor.

The inducing activity of the vegetalizing factor decreases after covalent coupling to CNBr-Sepharose with reduced binding capacity. The residual inducing activity is probably due to the release of a small amount of the factor from Sepharose beads. Covalent coupling to activated CH-Sepharose completely inactivated the vegetalizing factor, whereas the neuralizing factor retained its full activity.

A new method for the isolation of plasma membranes from amphibian embryos.

A method for the isolation of plasma membranes is described. N-Succinimidyl 3-(2-pyridyldithio) propionate (SPDP), a heterobifunctional reagent, is covalently linked to protein amino groups in plasma membranes of intact cells. After homogenization of the cells the plasma membranes can be separated from other cell components by selective coupling to reduced Thiopropyl-Sepharose 6B and then recovered after treatment with 2-mercaptoethanol.

Changes of the cell surface charge of amphibian ectoderm after induction.

Isolated ectoderm of early gastrula stages ofTriturus alpestris was treated with vegetalizing factor for 24 h employing the sandwich method (induced ectoderm). Controls were incubated for the same period with γ-globulin which has no inducing activity. Explants of both series were labelled with cationized ferritin, which binds to negatively charged groups at physiological pH.

Change of the differentiation pattern of amphibian ectoderm after the increase of the initial cell mass.

Early amphibian gastrula ectoderm (Triturus alpestris) has been treated with vegetalizing factor. While normal sandwiches (animal caps of two eggs) differentiated mainly into endoderm derived tissues, giant-sandwiches (a combination of 8 animal caps) formed mesodermal and neural tissues in addition. The results support the interpretation that ectoderm will differentiate into endoderm derived tissues when all or nearly all cells are induced (presumably depending on certain threshold concentrations of the inducer).

Differentiation of the four animal and the four vegetal blastomeres of the eight-cell-stage ofTriturus alpestris.

The 4 animal and 4 vegetal blastomeres of the eight-cell-stage ofTriturus alpestris were isolated and cultured for up to 12 days. Because of the difficulty of obtaining intact animal and vegetal blastomeres of the same embryo, we either cut off the vegetal blastomeres or sucked off the animal blastomeres. The culture of early embryonic amphibian cells is improved by the use of 50% Leibovitz-medium with added fetal calf serum providing a stable pH and optimal osmotic pressure.

Influence of cyclic nucleotides on amphibian ectoderm.

Isolated amphibian (Triturus alpestris) gastrula ectoderm was treated with cyclic nucleotides for 24 h and cultured up to 12 days. Explants treated with$cyclic N-Monobutyryl-adenosine-3'∶5'-monophosphate, cyclic Dibutyryladenosine-3'∶5'-monophosphate and cyclic Dibutyrylguanosine-3'∶5'-monophosphate in a concentration of 10 and 10 M did not differentiate into mesoderm- or endoderm-derived tissues. The number of explants with small neural and neuroid structures did not exceed the percentage found in the control series.

The differentiation of isolated amphibian ectoderm with or without treatment with an inductor : A scanning electron microscop study.

Amphibian gastrula ectoderm was isolated and examined by scanning electron microscopy after 24 h, 48 h, 6 and 10 days in culture.Contrary to the view which was formerly held, ectoderm is already detemined to form epidermis at the early gastrula stage. The ultrastructural differentiation of the epidermal cellsin vitro is very similar to their developmentin vivo (Billettet al.