Persistent ultrastructural changes in pancreatic acinar cells induced by 4-acetylaminofluorene

Male Leeds rats were fed a diet containing 0.05% of the non-carcinogen 4-acetylaminofluorene (4-AAF) for 8–10 months. They were then returned to a normal diet and their pancreatic tissues examined by electron microscopy at intervals between 2 and 12 months after the end of 4-AAF treatment. 4-AAF was found to induce a persistent alteration in the morphology of the granular endoplasmic reticulum, involving distortion and dilatation of the cisternae. In some respects this lesion resembles that which is induced by the carcinogenic isomer, 2-acetylaminofluorene (2-AAF).     

Failure of spermatozoa from T/t mice to fertilize in vitro is overcome by zona drilling

Failure of epididymal spermatozoa from T/t mutant mice, but not from t/t individuals, to fertilize oocytes in vitro was partially overcome by opening a small aperture in the zona pellucida with acidified Tyrode's solution to permit direct access of the spermatozoon to the vitellus. This study provides a model system to evaluate requirements for successful zona drilling in the treatment of human infertility and further insights into the effects of the t complex on sperm fertility.     

Developmental Changes in the Calcium Dependency of γ-Aminobutyric Acid Release from Isolated Growth Cones: Correlation with Growth Cone Morphology

We have investigated the development of Ca2+-dependent gamma-[3H]aminobutyric acid [( 3H]GABA) release in superfused growth cone fractions isolated from rats between the postnatal ages of 1 and 11 days. We have compared this release with the overall morphology of the subcellular fractions, and identified those structures taking up [3H]GABA by electron microscopical autoradiography. In fractions isolated from rats between 1 and 5 days, K+-evoked [3H]GABA release was completely independent of extracellular Ca2+. After 5 days a Ca2+ dependency appeared, which increased with age, such that by 10 days approximately 50% of the K+-evoked release was Ca2+ dependent. Electron microscopical analysis showed that, at all ages, large numbers of GABAergic growth cones were present in the subcellular fractions. Up to postnatal day 5, the growth cones were synaptic vesicle sparse but, after this age, increasing numbers of synaptic vesicle-containing growth cones were seen. These results suggest that during maturation of GABAergic growth cones into synapses there is, initially, a mechanism for release that is independent of extracellular Ca2+ and that the appearance of a Ca2+-dependent [3H]GABA release from growth cones correlates with the appearance of synaptic vesicles.     

A human glial hybrid cell line differentially expressing genes subserving oligodendrocyte and astrocyte phenotype

We have developed a series of immortal human-human hybrid cell lines that express phenotypic characteristics of primary oligodendrocytes, by fusing a 6-thioguanine–resistant mutant of the human rhabdomyosarcoma RD with adult human oligodendrocytes by a lectin-enhanced polyethylene glycol procedure. Hybrids were selected in an aminopterin-containing media. In contrast to the tumor parent cells, a hybrid clone M03.13 expressed surface immunoreactivity for galactosyl cerebroside and intracellular immunoreactivity for myelin basic protein (MBP), proteolipid protein (PLP), and glial fibrillary acidic protein (GFAP). Serum deprivation or chronic treatment with a protein kinase C activator 4-β-phorbol 12-myristate 13-acetate (PMA), but not dibutyl cyclic adenosine monophosphate induced coordinate up-regulation or de novo induction of oligodendrocyte phenotypic markers with concomitant down-regulation of GFAP expression. Consistent with immunohistochemical studies, northern blot analysis demonstrated that both MBP and PLP mRNA were up-regulated in MO3.13 cells by PMA treatment. M03.13 cells provide an immortalized clonal model system suitable for study of gene expression subserving oligodendrocyte and astrocyte phenotypes. © 1995 John Wiley & Sons, Inc.     

Bloom Syndrome and Maternal Uniparental Disomy for Chromosome 15

Bloom syndrome (BS) is an autosomal recessive disorder characterized by increases in the frequency of sister-chromatid exchange and in the incidence of malignancy. Chromosome-transfer studies have shown the BS locus to map to chromosome 15q. This report describes a subject with features of both BS and Prader-Willi syndrome (PWS). Molecular analysis showed maternal uniparental disomy for chromosome 15. Meiotic recombination between the two disomic chromosomes 15 has resulted in heterodisomy for proximal 15q and isodisomy for distal 15q. In this individual BS is probably due to homozygosity for a gene that is telomeric to D15S95 (15q25), rather than to genetic imprinting, the mechanism responsible for the development of PWS. This report represents the first application of disomy analysis to the regional localization of a disease gene. This strategy promises to be useful in the genetic mapping of other uncommon autosomal recessive conditions.     

Immunolocalization of alpha-transforming growth factor in the developing rat mammary gland in vivo, rat mammary cells in vitro and in human breast diseases

Summary Immunoreactive alpha-transforming growth factor (-TGF) was shown by immunocytochemistry to be present in the rat mammary gland at various stages of development, the staining being most intense in mature myoepithelial cells. -TGF was also detected in the secretions of the mammary glands of pregnant and lactating rats. -TGF in the extracts of rat mammary glands at each stage of development, and in several rat mammary cell lines and in culture medium in which they had been grown, was shown by Western blotting to consist primarily of a protein of molecular weight 50 kDa. The amount of this protein was greater in the mammary gland of the lactating rat than in resting or involuting glands. -TGF was also found in some, but not all, human breast carcinomas, and in benign hyperplastic breast diseases.     

Influence of nitrate on uptake of ammonium by nitrogen-depleted soybean: is the effect located in roots or shoots?

In non-nodulated soybean [Glycine max (L.) Merrill cv. Ransom]plants that were subjected to 15 d of nitrogen deprivation inflowing hydroponic culture, concentrations of nitrogen declinedto 1.0 and 1.4mmol Ng^–1 dry weight in shoots and roots,respectively, and the concentration of soluble amino acids (determinedas primary amines) declined to 40µmol g^–1 dry weightin both shoots and roots. In one experiment, nitrogen was resuppliedfor 10 d to one set of nitrogen-depleted plants as 1.0 mol m^–3NH₄⁺ to the whole root system, to a second set as 0.5 mol m^–3NH₄⁺ plus 0.5 mol m^–3 NO₃^– to the whole root system,and to a third set as 1.0 mol m^–3 NH₄⁺ to one-half ofa split-root system and 1.0 mol m^–3 NO₃^– to theother half. In a second experiment, 1.0 mol m^–3 of nitrogenwas resupplied for 4 d to whole root systems in NH₄⁺ : NO₃^–ratios of 1:0, 9:1, and 1:1. Nutrient solutions were maintainedat pH 6.0. When NH₄⁺ was resupplied in combination with NO₃^– to thewhole root system in Experiment I, cumulative uptake of NH₄⁺for the 10 d of resupply was about twice as great as when NH₄⁺was resupplied alone. Also, about twice as much NH₄⁺ as NO₃^–was taken up when both ions were resupplied to the whole rootsystem. When NH₄⁺ and NO₃^– were resupplied to separatehalves of a split-root system, however, cumulative uptake ofNH₄⁺ was about half that of NO₃^–. The uptake of NH₄⁺,which is inhibited in nitrogen-depleted plants, thus is facilitatedby the presence of exogenous NO₃^–, and the stimulatingeffect of NO₃^– on uptake of NH₄⁺ appears to be confinedto processes within root tissues. In Experiment II, resupplyof nitrogen as both NH₄⁺ and NO₃^– in a ratio of either1:1 or 9:1 enhanced the uptake of NH₄⁺. The enhancement of NH₄⁺uptake was 1.8-fold greater when the NH₄⁺: NO₃^–-resupplyratio was 1:1 than when it was 9:1; however, only 1.3 timesas much NO₃^– was taken up by plants resupplied with the1 :1 exogenous ratio. The effect of NO₃^– on enhancementof uptake of NH₄⁺ apparently involves more than net uptake ofNO₃^– itself and perhaps entails an effect of NO₃^–uptake on maintenance of K⁺ availability within the plant. Theconcentration of K⁺ in plants declined slightly during nitrogendeprivation and continued to decline following resupply of nitrogen.The greatest decline in K⁺ concentration occurred when nitrogenwas resupplied as NH₄⁺ alone. It is proposed that decreasedavailability of K⁺ within the NH₄⁺-resup-plied plants inhibitedNH₄⁺ uptake through restricted transfer of amino acids fromthe root symplasm into the xylem. Key words: Ammonium, Glycine max, nitrate, nitrogen-nutrition, nitrogen stress, split-root cultures     

Spotlight on phytochrome nomenclature

These recommendations for genes encoding phytochromes were developed independently by Quail et al., but are broadly consistent with the Commission's guidelines. Their original article, kindly provided in advance of publication, appeared as a Letter to the Editor inPlant Cell (6:468–471, 1994) and is published with permission of the American Society of Plant Physiologists.     

Host selection and survival of the parasitoidEncarsia formosa on greenhouse whitefly,Trialeurodes vaporariorum, in the presence of hosts infected with the fungusAschersonia aleyrodis

Successful control of greenhouse whitefly may be achieved by complementary activity of the parasitoidEncarsia formosa and the fungusAschersonia aleyrodis. One way to obtain an additive mortality effect of both entomopathogen and parasitoid would be achieved by the selection of healthy hosts by the parasitoid and rejection of fungus-infected hosts. Third and fourth instar larvae ofTrialeurodes vaporariorum which had been treated with a spore suspension ofA. aleyrodis 0, 4, 7, 10 or 14 days beforehand, were presented to female parasitoids. The parasitoids adopted the oviposition posture on untreated hosts as well as on treated hosts, irrespective of the different stages of infection in the hosts. However, significantly more hosts were parasitized byE. formosa in the control treatment than in the fungal treatment. The parasitoids offered treated hosts, showed rejection behaviour after probing on hosts showing detectable signs of infection (containing hyphal bodies or mycelium in the haemolymph). For instance, when hosts were offered seven days after spore treatment, the parasitoids showed an oviposition posture on a total of 83 (95.4%) out of 87 infected larvae, but laid only 4 eggs (4.6%). In contrast, on 48 (94.1%) out of 51 noninfected (or showing no detectable signs of infection) hosts an oviposition posture was adopted and 40 eggs (78.4%) were found after dissection. When infected hosts were encountered the oviposition posture lasted less than 1′40″ while rejection of non-infected hosts occurred after more than 1′40″. Other experiments were carried out offering treated hosts for 24 h to the parasitoids. The hosts were dissected afterwards. Again, significantly more eggs were laid in the non-infected hosts. When hosts were parasitized shortly after fungal spore treatment they were colonized by the fungus and the parasitoids did not develop. Transmission of the entomopathogen after probing infected hosts was observed to a limited extent. In conclusion,A. aleyrodis andE. formosa can be used together in a glasshouse situation. The parasitoid will be most effective when introduced more than seven days after application ofA. aleyrodis, because from that time onwards it is able to detect and reject fungus-infected hosts.