The exchange of isotopic water, 2H2O and H2(18)O has been studied in amphibian eggs. The experiments were carried out with ovarian and body cavity eggs of Rana temporaria and unfertilized eggs of Ambystoma mexicanum. The cytoplasmic diffusion coefficient for H2(18)O was found to be 4.6 x 10(-6) cm2/s, somewhat higher than that for 2H2O, 3.4 x 10(-6) cm2/s. The total change in reduced weight, delta RW, during the isotope experiments was compared with the total amount of water in the egg cell, m. The ratio delta RW/m was significantly higher than would be expected from calculations using ordinary water density values. The results are discussed in terms of different phases of structured cell water.

Ambystoma↗

PubMed1979

Fate maps and cell differentiation in the amphibian embryo--an experimental study.

The aim of this paper is to test two different fate maps for the amphibian blastula with respect to their predictions concerning the process of cell differentiation. The first of these fate maps is the one proposed by Vogt, according to which all three germ layers can be projected on to the surface of the embryo. The second is a revision which claims that only endoderm and ectoderm are located in the surface, while the mesoderm is represented by free cells in the interior of the embryo. The testing has been performed by observing the differentiation of small explants of cells taken from various regions of the embryo. It was found that the spontaneous cell differentiation comprises three patterns: undifferentiated cells (free interior cells and circumpolar endodermal cells), fibroblast-like cells (the remaining endodermal cells) and epidermis (ectodermal cells). Further differentiation occurs only through induction, exerted either by the fibroblast-like endodermal cells or by heparan sulphate. When induced, the equatorial ectodermal cells give rise to swollen, hyaline cells (chordocytes), while the remaining ectodermal cells form a sequence of cell differentiation patterns, mesenchyme cells, nerve cells, melanophores and xanthophores. The free interior cells differentiate into striated muscle cells and elongated collagen-producing fibroblasts. Our results thus confirm the revised fate map, and they also give an insight into the mechanisms of the initial cell differentiations in the amphibian embryo.

Ambystoma↗

PubMed1978

Metabolism of cold-stored pancreatic islets.

A previous study showed that the ability of glucose to stimulate insulin release was retained in islets stored at 8 degrees C for one week provided that glucose was present in a high concentration in the storage medium. The metabolic properties of islets stored in the cold have now been further explored in an attempt to clarify the protective effect of glucose. During storage in the cold the islet formation of 3H2O from (5--3H) glucose and oxygen consumption were only a few per cent of that of fresh islets whereas the putake of 86Rb+ was 20--48%. Rewarming the cold-stored islets to 37 degrees C after one week of cold-storage restored the 86Rb+ uptake, the formation of 3H2O and 14CO2 from labelled glucose and oxygen consumption to 75, 80, 60 and 40% respectively of fresh islet levels. The results emphasize the usefulness of cold-storage for preservation of functionally intact isolated islets.

Animals↗

PubMed1978

Lactate--a suppressor of differentiation in embryonic cells.

All kinds of visible differentiation in cultured amphibian embryonic cells are suppressed in the presence of lactate. This effect differs in certain respects from that observed with actinomycin, but like the latter lactate inhibits RNA synthesis. In this communication we present some further observations on the effect of lactate.

Ambystoma↗

PubMed1978

Preliminary observations on the synthesis of glycosaminoglycans in the sea urchin embryo.

A method based on the degradation by enzymes and nitrous acid of isotopically labelled glycosaminoglycans has been employed to study the synthesis of these compounds in normal, animalized and vegetalized sea urchin embryos. According to standard criteria, these organisms synthesize dermatan sulfate, heparan sulfate, hyaluronate and keratan sulfate. The hyaluronate seems to be slightly sulfated, it may thus be mucoitin sulfate. The preliminary results obtained suggest a conspicuous difference between animalized and vegetalized embryos: the synthesis of dermatan sulfate is suppressed in the former, while proceeding normally in the latter. The synthesis of heparan sulfate is not affected by our experimental conditions, but the isotope incorporation in hyaluronate and in keratan sulfate is decreased, more in the vegetalized than in the animalized embryos.

Animals↗

PubMed1978

Robert Chambers, Charles Darwin and the mechanism of evolution.

Explore the source record for details and available documents.

Biological Evolution↗

PubMed1975

Control of cell division and cell differentiation by deoxynucleotides in the early embryo of Xenopus laevis.

It is proposed that the deoxyriboside triphosphates present in the egg of Xenopus laevis support the synchronous cell divisions occurring during the earliest phase of embryonic development and that, as long as synchrony prevails, the cells are prevented from undergoing differentiation. This hypothesis has been tested by injecting deoxyribonucleotides into fertilized eggs. The following effects were observed: 1) the duration of synchrony is prolonged, 2) the morphological development is suppressed, an effect which is greatest when four nucleotides are injected together and 3) the synthesis of all kinds of RNA is inhibited, including the mRNA required for differentiation to occur.

Adenosine Triphosphate↗

PubMed1953