The pattern of proliferation of the neuroblasts in the wild-type embryo of Drosophila melanogaster

Summary The pattern of neuroblast divisions was studied in thoracic and abdominal neuromeres of wild-type Drosophila melanogaster embryos stained with a monoclonal antibody directed against a chromatin-associated antigen. Since fixed material was used, our conclusions are based upon the statistical evaluation of a large number of accurately staged embryos, covering the stages between the formation of the cephalic furrow up to shortened germ band. Our observations point to a rather stereotypic pattern of proliferation, consisting of several parasynchronous cycles of division. The data suggest that all SI neuroblasts divide at least eight times, all SII neuroblasts six or seven times and all SIII neuroblasts at least five times. This conclusion is based on the mapping of mitotic neuroblasts and is supported by the progressive reduction of the neuroblast volume and by the results of cell countings performed on embryos of increasing age. No conclusive evidence was obtained concerning the fate of the neuroblasts after their last mitosis, i.e. it cannot be decided whether the neuroblasts degenerate or become incorporated as inconspicuous cells in the larval ventral cord. The duration of the cycles of division of the neuroblasts was found to be 40–50 min each, while in the case of ganglion mother cells about 100 min are required to complete one cell cycle.     

The organization of repetitive sequences in the albumin and alpha-fetoprotein gene loci in the rat

Summary The distribution of middle repetitive sequences in the genic and extragenic regions of the rat albumin and -fetoprotein genes was analyzed. Their presence was determined by probing Southern blots of restriction fragments of albumin and -fetoprotein genomic subclones with ³²P-labeled total rat DNA. Repetitive sequences were detected in both genes. They were classified as weak, moderate and intense hybridizing elements according to the intensity of hybridization. Weak repetitive sequences were characterized as dG·dT repeats by using ³²P-labeled poly-(dG·dT)(dC·dA) oligomer probe. They occurred in 5 and 3 extragenic regions of the two genes and in introns 4 and 5 of the albumin gene. The moderate repetitive sequence present in intron 6 of the albumin gene was identified as the rat SINES element, 4D12. The intense repetitive sequence, localized in the 3 non-coding region of the albumin gene, corresponded to the terminal segment of a rat high repeat long interspersed DNA family, L1Rn. 4D12 and L1Rn sequences were also scattered throughout the -fetoprotein locus as moderate and intense repetitive elements, respectively, but their distribution was different from that of the albumin genomic region. These results indicate that repetitive sequences invaded the two loci in a non-conservative manner.     

Sucrose transport into the phloem of Ricinus communis L. seedlings as measured by the analysis of sieve-tube sap

Careful cutting of the hypocotyl of Ricinus communis L. seedlings led to the exudation of pure sieve-tube sap for 2–3 h. This offered the possibility of testing the phloem-loading system qualitatively and quantitatively by incubating the cotyledons with different solutes of various concentrations to determine whether or not these solutes were loaded into the sieve tubes. The concentration which was achieved by loading and the time course could also be documented. This study concentrated on the loading of sucrose because it is the major naturally translocated sieve-tube compound. The sucrose concentration of sieve-tube sap was approx. 300 mM when the cotyledons were buried in the endosperm. When the cotyledons were excised from the endosperm and incubated in buffer, the sucrose concentration decreased gradually to 80–100 mM. This sucrose level was maintained for several hours by starch breakdown. Incubation of the excised cotyledons in sucrose caused the sucrose concentration in the sieve tubes to rise from 80 to 400 mM, depending on the sucrose concentration in the medium. Thus the sucrose concentration in the sieve tubes could be manipulated over a wide range. The transfer of labelled sucrose to the sieve-tube sap took 10 min; full isotope equilibration was finally reached after 2 h. An increase of K⁺ in the medium or in the sieve tubes did not change the sucrose concentration in the sievetube sap. Similarly the experimentally induced change of sucrose concentration in the sieve tubes did not affect the K⁺ concentration in the exudate. High concentrations of K⁺, however, strongly reduced the flow rate of exudation. Similar results were obtained with Na⁺ (data not shown). The minimum translocation speed in the sieve tubes in vivo was calculated from the growth increment of the seedling to be 1.03 m·h^-1, a value, which on average was also obtained for the exudation system with the endosperm attached. This comparison of the in-vivo rate of phloem transport and the exudation rate from cut hypocotyls indicates that sink control of phloem transport in the seedlings of that particular age was small, if there was any at all, and that the results from the experimental exudation system were probably not falsified by removal of the sink tissues.Abbreviations PTS 3-hydroxy-5,8, 10-pyrenetrisulfonate     

Localization of the nerve growth factor receptor on fetal human schwann cells in culture

Previous studies have established that Schwann cells (SC) in culture express an NGF receptor. In this study, cultures of fetal human SC were established from fetal nerves and various light microscopic (LM) and electron microscopic (EM) techniques were used to localize the NGF receptor on the SC. Results indicate that NGF receptor is localized to the plasma membrane of the SC. Quantitative digital analysis determined that the distal portion of the SC process had high concentrations of NGF receptor. The possible functional significance of this latter observation is discussed in terms of SC migration and ensheathment of axons.     

Histochemical detection of monoamine oxidase and alcohol dehydrogenase activities in the Syrian hamster Harderian glands: existence of a sexual dimorphism

Summary Monoamine oxidase (MAO) and alcohol dehydrogenase (AD) activities were studied histochemically in the Syrian hamster Harderian gland using tryptamine as substrate and Nitroblue Tetrazolium as the final electron acceptor. No dark: light-related changes were observed. Male type I secretory cells showed an intense MAO reaction. Female type I cells exhibited a moderate MAO activity. Both male and female glands showed a moderate/intense AD-positive reaction. Male type II cells were lacking MAO and AD activities. MAO activity found in the hamster Harderian glands corresponded mainly to MAO type A since treatment with chlorgyline (0.01, 0.1 and 0.5mm) totally inhibited it. The possible role of these two enzymes in Harderian gland indolalkylamine metabolism is discussed.     

Ca2+ ionophores inhibit superoxide generation by chemotactic peptide in rabbit neutrophils and the correlation with intracellular calcium

Summary Effects of Ca²⁺ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca²⁺ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca²⁺ concentration and is related to release of Ca²⁺ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca²⁺ modulation.Abbreviations FMLP Formyl-Methionyl-Leucyl-Phenylalanine methyl ester     

Fermentation parameters of Peptostreptococcus productus on gaseous substrates (CO,H2/CO2)

Intrinsic growth and substrate uptake parameters were obtained for Peptostreptococcus productus, strain U-1, using carbon monoxide as the limiting substrate. A modified Monod model with substrate inhibition was used for modeling. In addition, a product yield of 0.25 mol acetate/mol CO and a cell yield of 0.034 g cells/g CO were obtained. While CO was found to be the primary substrate, P. productus is able to produce acetate from CO₂ and H₂, although this substrate could not sustain growth. Yeast extract was found to also be a growth substrate. A yield of 0.017 g cell/g yeast extract and a product yield of 0.14 g acetate/g yeast extract were obtained. In the presence of acetate, the maximum specific CO uptake rate was increased by 40% compared to the maximum without acetate present. Cell replication was inhibited at acetate concentrations of 30 g/l. Methionine was found to be an essential nutrient for growth and CO uptake by P. productus. A minimum amount of a complex medium such as yeast extract (0.01%) is, however, required.     

Effects of the administration of cadmium and zinc on the concentration of zinc in the thymus of rats

The zinc content of thymus glands of male Wistar rats has been determined during five weeks of treatment with ZnCl₂ and CdCl₂, and compared with a group of control rats. THymus gland extracts were chromatographed on columns of Sephadex G-75 and the zinc content of the one hundred fractions obtained were determined by atomic absorption spectrophotometry. The rats treated with ZnCl₂ showed an increase in the thymus concentration of zinc bound to high and low molecular weight proteins. The rats treated with CdCl₂ showed an increase in zinc concentration, as opposed to the control group, during the first three weeks of treatment, and thereafter show a toxic effect of cadmium on the gland, with ulterior regression of the latter, and a decrease in the concentration of zinc.     

Occurrence of a Large Ca2+-Independent Release of Glutamate During Anoxia in Isolated Nerve Terminals (Synaptosomes)

Isolated rat cerebral cortical synaptosomes made anoxic by addition of cyanide developed an inhibition of the Ca2+-dependent release of glutamate 2 min after the addition of the metabolic inhibitor when the intrasynaptosomal ATP/ADP ratio decreased below 1.7. In contrast, cyanide induced a continuous efflux of glutamate through a Ca2+-independent pathway that accounted for the release of 25% of total intrasynaptosomal glutamate in 5 min. The results suggest that a Ca2+-independent release of glutamate could be implicated in the neurotoxic action of this amino acid during anoxia.     

Active glycolysis and glycogenolysis in early stages of primary cultured hepatocytes. Role of AMP and fructose 2.6-bisphosphate

Summary This study examines the factors involved in the rapid glycolysis and glycogenolysis that occur during the first stages of hepatocyte culture: a) Shortly after seeding glycolysis, estimated as lactate released to culture medium, increased 10 times in comparison to that reported in vivo. By 8 to 9 h of culture, hepatocytes were nearly glycogen-depleted even in the presence of insulin. b) 6-Phosphofructo-2-kinase remained 100% active during this period. The proportion of the initial active phosphorylase (87%) decreased to 57% by 7 h of culture. c) Fructose 2,6-bisphosphate content was initially similar to that found in liver of fed animals, decreased after seeding and increased thereafter up to four times the initial concentration. In spite of changes in the concentration of this activator, the glycolytic rate remained high and constant. d) ADP and AMP increased sharply after cell plating, reaching values 1.7 and 3.5 times higher. The rise in AMP levels may be involved in the activation of glycolysis and glycogenolysis, because this metabolite is known to act as an allosteric activator of phosphofrucktokinase and glycogen phosphorylase. This metabolic situation resembles that of cells under hypoxia. Part of this work was presented at the 38th Annual Meeting of the Tissue Culture Association, Washington, DC, May 1987.